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14 pages, 6591 KiB

Open AccessArticle

Preparation and Characterization of DOPO-Functionalized MWCNT and Its High Flame-Retardant Performance in Epoxy Nanocomposites

by Liqiang Gu, Chen Qiu, Jianhui Qiu, Youwei Yao, Eiichi Sakai and Liting Yang

Polymers 2020, 12(3), 613; https://doi.org/10.3390/polym12030613 - 7 Mar 2020

Cited by 34 | Viewed by 4429

Abstract

In this work, functionalized multi-walled carbon nanotubes (MWCNT) were synthesized by the reaction between acylated MWCNT and 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB). The obtained MWCNT-ODOPB was well dispersed into epoxy resins together with aluminum diethylphosphinate (AlPi) to form flame-retardant nanocomposites. The epoxy resin nanocomposite with phosphorus [...] Read more.

In this work, functionalized multi-walled carbon nanotubes (MWCNT) were synthesized by the reaction between acylated MWCNT and 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (ODOPB). The obtained MWCNT-ODOPB was well dispersed into epoxy resins together with aluminum diethylphosphinate (AlPi) to form flame-retardant nanocomposites. The epoxy resin nanocomposite with phosphorus content of 1.00 wt % met UL 94 V-0 rating, exhibited LOI value of 39.5, and had a higher T_g compared to neat epoxy resin, which indicates its excellent flame retardant performance. These experimental results indicated that MWCNT-ODOPB was a compatible and efficient flame retardant for epoxy resins. Moreover, cone calorimeter analysis showed that the peak heat release rate (pHRR), total heat release (THR) values, and CO₂ production profiles of the composites decreased with an increase in the additional amount of phosphorus. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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13 pages, 1878 KiB

Open AccessArticle

Development of Interfacial Adhesive Property by Novel Anti-Stripping Composite between Acidic Aggregate and Asphalt

by Guohong Zhang, Jianhui Qiu, Jingzhuo Zhao, Dingbang Wei and Hui Wang

Polymers 2020, 12(2), 473; https://doi.org/10.3390/polym12020473 - 19 Feb 2020

Cited by 13 | Viewed by 2808

Abstract

Studies on control of and preventive measures against asphalt pavement moisture damage have important economic and social significance due to the multiple damage and repair of pavements, the reasons for which include the poor interfacial adhesive ability between acidic aggregates and asphalts. Anti-stripping [...] Read more.

Studies on control of and preventive measures against asphalt pavement moisture damage have important economic and social significance due to the multiple damage and repair of pavements, the reasons for which include the poor interfacial adhesive ability between acidic aggregates and asphalts. Anti-stripping agent is used in order to improve the poor adhesion, and decomposition temperature is regarded as being important for lots of anti-stripping products, because they always decompose and lose their abilities under the high temperature in the mixing plant before application to the pavement. A novel anti-stripping composite, montmorillonoid/Polyamide (OMMT/PAR), which possesses excellent thermal stability performance and is effective in preventing moisture damage, especially for acidic aggregates, was prepared. Moreover, the modification mechanisms and pavement properties were also investigated with reference to the composites. The results show that OMMT/PAR was prepared successfully, improving the interfacial adhesion between the acidic aggregate and the modified asphalt. Due to the nanostructure of OMMT/PAR, the thermal stability was enhanced dramatically and the interfacial adhesion properties were also improved. Furthermore, asphalts modified with OMMT/PAR and their mixtures showed excellent properties. Finally, the moisture damage process and the mechanisms by which OMMT/PAR improves the interfacial adhesion properties are explained through adhesion mechanism analyses. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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17 pages, 7434 KiB

Open AccessArticle

The Formation Mechanism of the Double Gas Layer in Gas-Assisted Extrusion and Its Influence on Plastic Micro-Tube Formation

by Tongke Liu, Xingyuan Huang, Cheng Luo and Duyang Wang

Polymers 2020, 12(2), 355; https://doi.org/10.3390/polym12020355 - 6 Feb 2020

Cited by 14 | Viewed by 2893

Abstract

The diameter of a micro-tube is very small and its wall thickness is very thin. Thus, when applying double-layer gas-assisted extrusion technology to process a micro-tube, it is necessary to find the suitable inlet gas pressure and a method for forming a stable [...] Read more.

The diameter of a micro-tube is very small and its wall thickness is very thin. Thus, when applying double-layer gas-assisted extrusion technology to process a micro-tube, it is necessary to find the suitable inlet gas pressure and a method for forming a stable double gas layer. In this study, a double-layer gas-assisted extrusion experiment is conducted and combined with a numerical simulation made by POLYFLOW to analyze the effect of inlet gas pressure on micro-tube extrusion molding and the rheological properties of the melt under different inlet gas pressures. A method of forming a stable double gas layer is proposed, and its formation mechanism is analyzed. The research shows that when the inlet gas pressure is large, the viscosity on the inner and outer wall surfaces of the melt is very low due to the effects of shear thinning, viscous dissipation, and the compression effect of the melt, so the melt does not easily adhere to the wall surface of the die, and a double gas layer can be formed. When the inlet gas pressure slowly decreases, the effects of shear thinning and viscous dissipation are weakened, but the gas and the melt were constantly displacing each other and reaching a new balanced state and the gas and melt changed rapidly and steadily in the process without sudden changes, so the melt still does not easily adhere to the wall of the die. Thus, in this experiment, we adjusted the inlet gas pressure to 5000 Pa first to ensure that the melt do not adhere to the wall surface and then slowly increased the inlet gas pressure to 10,000 Pa to reduce the viscosity of the melt. Lastly, we slowly decreased the inlet gas pressure to 1000 Pa to form a stable double gas layer. Using this method will not only facilitate the formation of a stable double gas layer, but can also accurately control the diameter of the micro-tube. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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15 pages, 5806 KiB

Open AccessArticle

Preparation of Polyaniline/Emulsion Microsphere Composite for Efficient Adsorption of Organic Dyes

by Yuanli Liu, Liushuo Song, Linlin Du, Peng Gao, Nuo Liang, Si Wu, Tsuyoshi Minami, Limin Zang, Chuanbai Yu and Xu Xu

Polymers 2020, 12(1), 167; https://doi.org/10.3390/polym12010167 - 9 Jan 2020

Cited by 36 | Viewed by 4951

Abstract

Surface-functionalized polymeric microspheres have wide applications in various areas. Herein, monodisperse poly(styrene–methyl methacrylate–acrylic acid) (PSMA) microspheres were prepared via emulsion polymerization. Polyaniline (PANI) was then coated on the PSMA surface via in situ polymerization, and a three-dimensional (3D) structured reticulate PANI/PSMA composite was, [...] Read more.

Surface-functionalized polymeric microspheres have wide applications in various areas. Herein, monodisperse poly(styrene–methyl methacrylate–acrylic acid) (PSMA) microspheres were prepared via emulsion polymerization. Polyaniline (PANI) was then coated on the PSMA surface via in situ polymerization, and a three-dimensional (3D) structured reticulate PANI/PSMA composite was, thus, obtained. The adsorption performance of the composite for organic dyes under different circumstances and the adsorption mechanism were studied. The obtained PANI/PSMA composite exhibited a high adsorption rate and adsorption capacity, as well as good adsorption selectivity toward methyl orange (MO). The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm. The maximum adsorption capacity for MO was 147.93 mg/g. After five cycles of adsorption–desorption, the removal rate remained higher than 90%, which indicated that the adsorbent has great recyclability. The adsorbent materials presented herein would be highly valuable for the removal of organic dyes from wastewater. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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10 pages, 2492 KiB

Open AccessArticle

GM-Improved Antiaging Effect of Acrylonitrile Butadiene Styrene in Different Thermal Environments

by Yuchao Wang, Ming Chen, Miaoyu Lan, Zhi Li, Shulai Lu and Guangfeng Wu

Polymers 2020, 12(1), 46; https://doi.org/10.3390/polym12010046 - 28 Dec 2019

Cited by 10 | Viewed by 3624

Abstract

A stabilizer called 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM) was mixed in acrylonitrile butadiene styrene (ABS) with the same amount of 9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (DSPDP), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076) and tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox 3114) to investigate the influence of additives on the antiaging effect of ABS in oven [...] Read more.

A stabilizer called 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (GM) was mixed in acrylonitrile butadiene styrene (ABS) with the same amount of 9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (DSPDP), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1076) and tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate (Irganox 3114) to investigate the influence of additives on the antiaging effect of ABS in oven aging or repeated extrusion aging. It was found that the ABS doped with the GM stabilizer showed a better yellowing resistance and thermal stability than the ABS doped with other antioxidants. Owing to the fact that the stabilizer can act on the free radicals before it has been peroxidized, it could trap the free radicals as a consequence of directly blocking the oxidation process of the active species, thus solving the problem of oxidative degradation of the materials from the source. This work provides guidance for improving thermal stability of ABS, indicating a promising potential for industrial application. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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16 pages, 5525 KiB

Open AccessArticle

Multi-Fold Enhancement in Compressive Properties of Polystyrene Foam Using Pre-delaminated Stearate Functionalized Layer Double Hydroxides

by Emmanuel O. Ogunsona, Koffi L. Dagnon and Nandika Anne D'Souza

Polymers 2020, 12(1), 8; https://doi.org/10.3390/polym12010008 - 19 Dec 2019

Cited by 4 | Viewed by 4002

Abstract

Developing an environmentally benign styrene foam is a critical environmental need. Supercritical CO₂ use in foams has proven to be a valuable path. Adding fillers to increase bubble nucleation has been pursued concurrently. A prominent filler used is high surface area fillers, [...] Read more.

Developing an environmentally benign styrene foam is a critical environmental need. Supercritical CO₂ use in foams has proven to be a valuable path. Adding fillers to increase bubble nucleation has been pursued concurrently. A prominent filler used is high surface area fillers, such as smectic clays. However, all studies to date show a limit of 152% in compressive moduli and 260% in the compressive stress. The values, even with such gains, limit structural application. A seminal work in 1987 by Suh and Cotton proved that carbonyl linkages in calcium carbonates and CO₂ interact and impact nucleation efficiency and performance in supercritical CO₂ foams. In this paper, a high surface area clay (layer double hydroxides) which begins in an exfoliated state, then functionalized with a long chain alkyl carboxylate (stearic acid) is synthesized. The result is a remarkable multi-fold improvement to the compressive properties in comparison to polystyrene (PS); a 268% and 512% increase in compressive modulus and strength, respectively. Using a pre-delaminated approach, the higher surface area was achieved in the clays. The presence of the stearate improved the interactions between the clay galleries and PS through hydrophobic-hydrophobic interactions. The glass transition temperature of the nanocomposites was observed to shift to higher values after foaming. The results point to a new path to increase performance using a pre-delaminated clay with functional groups for environmentally benign foams. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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16 pages, 4496 KiB

Open AccessArticle

Experimental, Numerical, and Analytical Study on The Effect of Graphene Oxide in The Mechanical Properties of a Solvent-Free Reinforced Epoxy Resin

by Sergio Horta Muñoz, María del Carmen Serna Moreno, José Miguel González-Domínguez, Pablo Antonio Morales-Rodríguez and Ester Vázquez

Polymers 2019, 11(12), 2115; https://doi.org/10.3390/polym11122115 - 16 Dec 2019

Cited by 9 | Viewed by 3435

Abstract

This paper presents a methodology for manufacturing nanocomposites from an epoxy resin reinforced with graphene oxide (GO) nanoparticles. A scalable and sustainable fabrication process, based on a solvent-free method, is proposed with the objective of achieving a high level of GO dispersion, while [...] Read more.

This paper presents a methodology for manufacturing nanocomposites from an epoxy resin reinforced with graphene oxide (GO) nanoparticles. A scalable and sustainable fabrication process, based on a solvent-free method, is proposed with the objective of achieving a high level of GO dispersion, while maintaining matrix performance. The results of three-point bending tests are examined by means of an analytical technique which allows determining the mechanical response of the material under tension and compression from flexural data. As result, an increase of 39% in the compressive elastic modulus of the nanocomposite is found with the addition of 0.3 wt % GO. In parallel, we described how the strain distribution and the failure modes vary with the amount of reinforcement based on digital image correlation (DIC) techniques and scanning electron microscopy (SEM). A novel analytical model, capable of predicting the influence of GO content on the elastic properties of the material, is obtained. Numerical simulations considering the experimental conditions are carried out. the full strain field given by the DIC system is successfully reproduced by means of the finite element method (FEM). While, the experimental failure is explained by the crack growth simulations using the eXtended finite element method (XFEM). Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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12 pages, 3780 KiB

Open AccessEditor’s ChoiceArticle

Flexure Behaviors of ABS-Based Composites Containing Carbon and Kevlar Fibers by Material Extrusion 3D Printing

by Kui Wang, Shixian Li, Yanni Rao, Yiyun Wu, Yong Peng, Song Yao, Honghao Zhang and Said Ahzi

Polymers 2019, 11(11), 1878; https://doi.org/10.3390/polym11111878 - 13 Nov 2019

Cited by 68 | Viewed by 7790

Abstract

Short-fiber-reinforced thermoplastics are popular for improving the mechanical properties exhibited by pristine thermoplastic materials. Due to the inherent conflict between strength and ductility, there are only a few successful cases of simultaneous enhancement of these two properties in polymer composite components. The objective [...] Read more.

Short-fiber-reinforced thermoplastics are popular for improving the mechanical properties exhibited by pristine thermoplastic materials. Due to the inherent conflict between strength and ductility, there are only a few successful cases of simultaneous enhancement of these two properties in polymer composite components. The objective of this work was to explore the feasibility of simultaneous enhancement of strength and ductility in ABS-based composites with short-carbon and Kevlar fiber reinforcement by material extrusion 3D printing (ME3DP). Microstructure characterization and measurement of thermal and mechanical properties were conducted to evaluate the fiber-reinforced ABS. The influence of printing raster orientation and build direction on the mechanical properties of material extrusion of 3D-printed composites was analyzed. Experimental results demonstrated that the reinforcement of the ABS-based composites by short-carbon and Kevlar fibers under optimized 3D-printing conditions led to balanced flexural strength and ductility. The ABS-based composites with a raster orientation of ±45° and side build direction presented the highest flexural behaviors among the samples in the current study. The main reason was attributed to the printed contour layers and the irregular zigzag paths, which could delay the initiation and propagation of microcracks. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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12 pages, 3218 KiB

Open AccessArticle

Nanofibrillar Green Composites of Polylactide/Polyhydroxyalkanoate Produced in Situ Due to Shear Induced Crystallization

by Iurii Vozniak, Ramin Hosseinnezhad, Jerzy Morawiec and Andrzej Galeski

Polymers 2019, 11(11), 1811; https://doi.org/10.3390/polym11111811 - 4 Nov 2019

Cited by 17 | Viewed by 3674

Abstract

This study addresses the new concept of in situ inducing fibrillar morphology (micro or nanofibrils) of a minority component based on the simultaneous occurrence of orientation and shear induced crystallization of polymer fibers directly at the stage of extrusion in a single step. [...] Read more.

This study addresses the new concept of in situ inducing fibrillar morphology (micro or nanofibrils) of a minority component based on the simultaneous occurrence of orientation and shear induced crystallization of polymer fibers directly at the stage of extrusion in a single step. This possibility is demonstrated by using two entirely bio-sourced polymers: polylactide (PLA) and polyhydroxyalkanoate (PHA) as components. The shear induced crystallization allowed crystallization of PHA nanofibers immediately after applying high shear rate and elongation strain, avoiding subsequent cooling to initiate crystallization. Shearing of PHA increased non-isothermal crystallization temperature by 50 °C and decreased the temperature range in which the transition from a molten state to a crystallized one occurs by 17 °C. SEM observations demonstrate the successful transformation of the dispersed PHA phase into nanofibrils with diameters of nearly 200 nm. The transition from the droplets of PHA to fibers causes the brittle-to-ductile transition of the PLA matrix at a low concentration of PHA and contributes to the simultaneous increase of its rigidity and strength. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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26 pages, 5225 KiB

Open AccessArticle

Crystalline Characteristics, Mechanical Properties, Thermal Degradation Kinetics and Hydration Behavior of Biodegradable Fibers Melt-Spun from Polyoxymethylene/Poly(l-lactic acid) Blends

by Jianhua Li, Yatao Wang, Xiaodong Wang and Dezhen Wu

Polymers 2019, 11(11), 1753; https://doi.org/10.3390/polym11111753 - 25 Oct 2019

Cited by 28 | Viewed by 4936

Abstract

A series of polyoxymethylene (POM)/poly(l-lactic acid) (PLLA) blends were prepared by melt extrusion, and their spinnability was confirmed by rheological characterizations, successive self-nucleation, and annealing thermal fractionation analysis. The bicomponent fibers were prepared by means of the melt-spinning and post-drawing technologies [...] Read more.

A series of polyoxymethylene (POM)/poly(l-lactic acid) (PLLA) blends were prepared by melt extrusion, and their spinnability was confirmed by rheological characterizations, successive self-nucleation, and annealing thermal fractionation analysis. The bicomponent fibers were prepared by means of the melt-spinning and post-drawing technologies using the above-obtained blends, and their morphology, crystalline orientation characteristics, mechanical performance, hydration behavior, and thermal degradation kinetics were studied extensively. The bicomponent fibers exhibited a uniform diameter distribution and compact texture at the ultimate draw ratio. Although the presence of PLLA reduced the crystallinity of the POM domain in the bicomponent fibers, the post-drawing process promoted the crystalline orientation of lamellar folded-chain crystallites due to the stress-induced crystallization effect and enhanced the crystallinity of the POM domain accordingly. As a result, the bicomponent fibers achieved the relatively high tensile strength of 791 MPa. The bicomponent fibers exhibited a partial hydration capability in both acid and alkali media and therefore could meet the requirement for serving as a type of biodegradable fibers. The introduction of PLLA slightly reduced the thermo-oxidative aging property and thermal stability of the bicomponent fibers. Such a combination of two polymers shortened the thermal lifetime of the bicomponent fibers, which could facilitate their natural degradation for ecological and sustainable applications. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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13 pages, 3335 KiB

Open AccessArticle

Fabrication and Properties of Superhydrophobic Waterborne Polyurethane Composites with Micro-Rough Surface Structure Using Electrostatic Spraying

by Fangfang Wang, Lajun Feng, Guangzhao Li, Zhe Zhai, Huini Ma, Bo Deng and Shengchao Zhang

Polymers 2019, 11(11), 1748; https://doi.org/10.3390/polym11111748 - 24 Oct 2019

Cited by 14 | Viewed by 3366

Abstract

Waterborne polyurethane (WPU) coatings hold advantages of good toughness, low cost and environmental protection. However, the low water contact angle (WCA), poor wear and corrosion resistance make them unsuitable for application in the superhydrophobic coatings such as antipollution flashover coatings for transmission lines, [...] Read more.

Waterborne polyurethane (WPU) coatings hold advantages of good toughness, low cost and environmental protection. However, the low water contact angle (WCA), poor wear and corrosion resistance make them unsuitable for application in the superhydrophobic coatings such as antipollution flashover coatings for transmission lines, self-cleaning coatings for outdoor equipment and waterproof textiles. A series of superhydrophobic WPU composites (SHWPUCs) with micro-rough surface structure was prepared by electrostatic spraying nano-SiO₂ particles on WPU composites with low surface energy. It showed that as the hydrophobic system content rose the WCAs of the composites first increased and then remained stationary; however, the adhesion and corrosion resistance first increased and then decreased. An appropriate addition of the hydrophobic system content would lead to a dense coating structure, but an excessive addition could increase the interfaces in the coating and then reduce the coating performance. When the mass ratio of the WPU dispersion, polytetrafluoroethylene (PTFE) particles and modified polydimethylsiloxane was 8:0.3:0.4, 10 g/m² nano-SiO₂ particles were sprayed on the uncured coating surface to construct the SHWPUC with a WCA of 156°. Compared with pure WPU coating, its adhesion and corrosion resistance increased by 12.5% and one order of magnitude, respectively; its wear rate decreased by 88.8%. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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28 pages, 7385 KiB

Open AccessArticle

Development of Polyoxymethylene/Polylactide Blends for a Potentially Biodegradable Material: Crystallization Kinetics, Lifespan Prediction, and Enzymatic Degradation Behavior

by Jianhua Li, Yatao Wang, Xiaodong Wang and Dezhen Wu

Polymers 2019, 11(9), 1516; https://doi.org/10.3390/polym11091516 - 18 Sep 2019

Cited by 15 | Viewed by 4280

Abstract

This paper reported the development of polyoxymethylene (POM)/polylactide (PLA) blends for a potentially biodegradable material. A series of POM/PLA blends at different weight ratios were prepared by melt extrusion with a twin-screw extruder, and their mechanical properties, crystallization behavior and kinetics, thermal degradation [...] Read more.

This paper reported the development of polyoxymethylene (POM)/polylactide (PLA) blends for a potentially biodegradable material. A series of POM/PLA blends at different weight ratios were prepared by melt extrusion with a twin-screw extruder, and their mechanical properties, crystallization behavior and kinetics, thermal degradation kinetics and stability, lifespan prediction and enzymatic degradation behavior were investigated extensively. POM and PLA were found to be partially miscible in the melt state at low temperature and become phase-separated at elevated temperatures, and their blends exhibited a typical lower critical solution temperature behavior. There were two distinct glass transition temperatures (T_g) observed for POM/PLA blends at any mass ratios when quenched from the homogeneous state, and both POM and PLA domains showed an apparent depression in their respective T_g’s in the blends. Owing to the partial miscibility between two domains, the tensile strength and impact toughness of POM/PLA blends gradually decreased with an increase of PLA content, but their flexural strength and modulus presented an increasing trend with PLA content. The studies on non-isothermal and isothermal crystallization behaviors of the blends indicated that the crystallization rates of the blends decreased continually with increasing the PLA content, confirming that the crystallization of POM domain was controlled by the molecular-confined mechanism. The introduction of PLA into POM not only led to a slight increase of thermal stability of POM domain at low PLA contents but also shortened the lifespan of the blends, favoring the natural degradation of the blends. The POM/PLA blends exhibited an improvement in partially biodegradable performance with an increase of PLA content and their mass loss reached up to 25.3 wt % at the end of 48-h enzymatic degradation when 50 wt % of PLA was incorporated. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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26 pages, 20861 KiB

Open AccessArticle

Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part A (Pressure Flows)

by Christian Marschik, Marius Dörner, Wolfgang Roland, Jürgen Miethlinger, Volker Schöppner and Georg Steinbichler

Polymers 2019, 11(9), 1488; https://doi.org/10.3390/polym11091488 - 12 Sep 2019

Cited by 7 | Viewed by 2600

Abstract

Wave-dispersion screws have been used industrially in many types of extrusion processes, injection molding, and blow molding. These high-performance screws are constructed by replacing the metering section of a conventional screw with a melt-conveying zone consisting of two or more parallel flow channels [...] Read more.

Wave-dispersion screws have been used industrially in many types of extrusion processes, injection molding, and blow molding. These high-performance screws are constructed by replacing the metering section of a conventional screw with a melt-conveying zone consisting of two or more parallel flow channels that oscillate periodically in-depth over multiple cycles. With the barrier flight between the screw channels being selectively undercut, the molten resin is strategically forced to flow across the secondary flight, assuring repeated cross-channel mixing of the polymer melt. Despite the industrial relevance, very few scientific studies have investigated the flow in wave-dispersion sections in detail. As a result, current screw designs are often based on traditional trial-and-error procedures rather than on the principles of extrusion theory. This study, which was split into two parts, was carried out to systematically address this issue. The research reported here (Part A) was designed to reduce the complexity of the problem, exclusively analyzing the pressure-induced flows of polymer melts in wave sections. Ignoring the influence of the screw rotation on the conveying characteristics of the wave section, the results could be clearly assigned to the governing type of flow mechanism, thereby providing a better understanding of the underlying physics. Experimental studies were performed on a novel extrusion die equipped with a dual wave-channel system with alternating channel depth profiles. A seminumerical modeling approach based on network theory is proposed that locally describes the downchannel and cross-channel flows along the wave channels and accurately predicts the pressure distributions in the flow domain. The solutions of our seminumerical approach were, moreover, compared to the results of three-dimensional non-Newtonian CFD simulations. The results of this study will be extended to real screw designs in Part B, which will include the influence of the screw rotation in the flow analysis. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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10 pages, 1262 KiB

Open AccessArticle

Thioetherimide-Modified Cyanate Ester Resin with Better Molding Performance for Glass Fiber Reinforced Composites

by Pengchang Ma, Chuntao Dai and Shaohua Jiang

Polymers 2019, 11(9), 1458; https://doi.org/10.3390/polym11091458 - 6 Sep 2019

Cited by 21 | Viewed by 3379

Abstract

Cyanate ester (CE) resins with higher heat resistance, lower coefficients of thermal expansion (CTEs), and lower water absorption ratios are highly desired in printed circuit boards (PCBs). In this work, a CE was modified by copolymerization with a long-chain thioether bismaleimide (SBMI) to [...] Read more.

Cyanate ester (CE) resins with higher heat resistance, lower coefficients of thermal expansion (CTEs), and lower water absorption ratios are highly desired in printed circuit boards (PCBs). In this work, a CE was modified by copolymerization with a long-chain thioether bismaleimide (SBMI) to form a thioetherimide-modified CE (SBT). The results indicated that SBT had a wider processing window and better processing properties than a common bismaleimide-modified CE resin (MBMI). After molding with a glass fiber cloth, the composites (GSBT) exhibited moisture adsorption in the range of 1.4%–2.0%, high tensile strength in the range of 311–439 MPa, good mechanical retention of 70%–85% even at 200 °C, and good dimension stability, with coefficients of thermal expansion in the range of 17.3–18.6 (×10⁻⁶ m/°C). Such GSBT composites with superior properties would be good candidates for PCB applications. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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15 pages, 5063 KiB

Open AccessArticle

In-mold and Machine Sensing and Feature Extraction for Optimized IC-tray Manufacturing

by Shih-Chih Nian, Yung-Chih Fang and Ming-Shyan Huang

Polymers 2019, 11(8), 1348; https://doi.org/10.3390/polym11081348 - 14 Aug 2019

Cited by 31 | Viewed by 6325

Abstract

Injection molding is a mature technology that has been used for decades; factors including processed raw materials, molds and machines, and the processing parameters can cause significant changes in product quality. Traditionally, researchers have attempted to improve injection molding quality by controlling screw [...] Read more.

Injection molding is a mature technology that has been used for decades; factors including processed raw materials, molds and machines, and the processing parameters can cause significant changes in product quality. Traditionally, researchers have attempted to improve injection molding quality by controlling screw position, injection and packing pressures, and mold and barrel temperatures. However, even when high precision control is applied, the geometry of the molded part tends to vary between different shots. Therefore, further research is needed to properly understand the factors affecting the melt in each cycle so that more effective control strategies can be implemented. In the past, injection molding was a “black box”, so when based on statistical experimental methods, computer-aided simulations or operator experience, the setting of ideal process parameters was often time consuming and limited. Using advanced sensing technology, the understanding of the injection molding process is transformed into a “grey box” that reveals the physical information about the flow behavior of the molten resin in the cavity. Using the process parameter setting data provided by the machine, this study developed a scientific method for optimal parameter adjustment, analyzing and interpreting the injection speed, injection pressure, cavity pressure, and the profile of the injection screw position. In addition, the main parameters for each phase are determined separately, including injection speed/pressure during the mold filling phase, velocity-to-pressure switching point, packing pressure and time. In this study, the IC tray was taken as an example. The experimental results show that the method can effectively reduce the warpage of the IC-tray from 0.67 mm to 0.20 mm. In addition, the parameters profiles obtained by parameter optimization can be applied for continuous mass production and process monitoring. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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12 pages, 4364 KiB

Open AccessArticle

High-Voltage Sulfolane Plasticized UV-Curable Gel Polymer Electrolyte

by Shiqi Wang, Chun Wei, Wenwen Ding, Linmin Zou, Yongyang Gong, Yuanli Liu, Limin Zang and Xu Xu

Polymers 2019, 11(8), 1306; https://doi.org/10.3390/polym11081306 - 4 Aug 2019

Cited by 10 | Viewed by 4663

Abstract

A high-voltage electrolyte can match high-voltage positive electrode material to fully exert its capacity. In this research, a sulfolane plasticized polymer electrolyte was prepared by in situ photocuring. First, the effect of the sulfolane content on the ionic conductivity of the gel polymer [...] Read more.

A high-voltage electrolyte can match high-voltage positive electrode material to fully exert its capacity. In this research, a sulfolane plasticized polymer electrolyte was prepared by in situ photocuring. First, the effect of the sulfolane content on the ionic conductivity of the gel polymer electrolyte was investigated. Results showed that the ionic conductivity variation trend was in good agreement with the exponential function model for curve fitting. Second, the activation energy was calculated from the results of the variable temperature conductivity tests. The activation energy was inversely proportional to the sulfolane content. For the sulfolane content of 80 wt. % in gel polymer electrolyte (GPE)-80 (19.5 kJ/mol), the activation energy was close to conventional liquid electrolyte (9.5 kJ/mol), and the conductivity and electrochemical window were 0.64 mS/cm and 5.86 V, respectively. The battery cycle performance test showed that the initial specific discharge capacities of GPE-80 and liquid electrolyte were 176.8 and 148.3 mAh/g, respectively. After 80 cycles, the discharge capacities of GPE-80 and liquid electrolyte were 115.8 and 41.1 mAh/g, and the capacity retention rates were 65.5% and 27.7%, respectively; indicating that GPE-80 has a better specific discharge capacity and cycling performance than the liquid electrolyte. SEM images indicated that GPE-80 can suppress the growth of lithium dendrites. The EDS test showed that GPE-80 can inhibit the dissolution of metal ions in the cathode material. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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17 pages, 4866 KiB

Open AccessArticle

Preparation and Properties of a High-Performance EOEOEA-Based Gel-Polymer-Electrolyte Lithium Battery

by Wenwen Ding, Chun Wei, Shiqi Wang, Linmin Zou, Yongyang Gong, Yuanli Liu and Limin Zang

Polymers 2019, 11(8), 1296; https://doi.org/10.3390/polym11081296 - 2 Aug 2019

Cited by 4 | Viewed by 5182

Abstract

Gel polymer electrolyte (GPE) is a promising candidate for lithium-ion batteries due to its adhesion property (like a solid), diffusion property (like a liquid), and inhibition of the growth of lithium dendrite. In this paper, 2-(2-ethoxyethoxy)ethyl acrylate (EOEOEA) and LiBF₄ electrolyte were [...] Read more.

Gel polymer electrolyte (GPE) is a promising candidate for lithium-ion batteries due to its adhesion property (like a solid), diffusion property (like a liquid), and inhibition of the growth of lithium dendrite. In this paper, 2-(2-ethoxyethoxy)ethyl acrylate (EOEOEA) and LiBF₄ electrolyte were mixed as precursors of gel polymer electrolytes. Through thermal curing, a thermally stable GPE with high ionic conductivity (5.60 × 10⁻⁴ s/cm at 30 °C) and wide room temperature electrochemical window (4.65 V) was prepared, and the properties of the GPE were measured by linear sweep voltammetry (LSV), AC impedance spectroscopy, Thermogravimetric analysis (TG), and X-ray diffraction (XRD) techniques. On the basis of the in-situ deep polymerization on a LiFePO₄ electrode and cellulose membrane in a battery case, EOEOEA-based GPE could be derived on both LiFePO₄ electrode and cellulose membrane. Meanwhile, the contact between GPE, LiFePO₄ electrode, and lithium electrode was promoted. The capacity retention rate of the as-prepared LiBF₄-EOEOEA 30% gel lithium battery reached 100% under the condition of 0.1 °C after 50 cycles, and the Coulombic efficiency was over 99%. Meanwhile, the growth of lithium dendrite could be effectively inhibited. GPE can be applied in high-performance lithium batteries. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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14 pages, 3909 KiB

Open AccessArticle

Structure and Mechanical Properties of Multi-Walled Carbon Nanotubes-Filled Isotactic Polypropylene Composites Treated by Pressurization at Different Rates

by Xiaoting Li, Wenxia Jia, Beibei Dong, Huan Yuan, Fengmei Su, Zhen Wang, Yaming Wang, Chuntai Liu, Changyu Shen and Chunguang Shao

Polymers 2019, 11(8), 1294; https://doi.org/10.3390/polym11081294 - 2 Aug 2019

Cited by 7 | Viewed by 3223

Abstract

Isotactic polypropylene filled with 1 wt.% multi-walled carbon nanotubes (iPP/MWCNTs) were prepared, and their crystallization behavior induced by pressurizing to 2.0 GPa with adjustable rates from 2.5 to 1.3 × 10⁴ MPa/s was studied. The obtained samples were characterized by combining wide [...] Read more.

Isotactic polypropylene filled with 1 wt.% multi-walled carbon nanotubes (iPP/MWCNTs) were prepared, and their crystallization behavior induced by pressurizing to 2.0 GPa with adjustable rates from 2.5 to 1.3 × 10⁴ MPa/s was studied. The obtained samples were characterized by combining wide angle X-ray diffraction, small angle X-ray scattering, differential scanning calorimetry, transmission electron microscopy and atomic force microscopy techniques. It was found that pressurization is a simple way to prepare iPP/MWCNTs composites in mesophase, γ-phase, or their blends. Two threshold pressurization rates marked as R₁ and R₂ were identified, while R₁ corresponds to the onset of mesomorphic iPP formation. When the pressurization rate is lower than R₁ only γ-phase generates, with its increasing mesophase begins to generate and coexist with γ-phase, and if it exceeds R₂ only mesophase can generate. When iPP/MWCNTs crystallized in γ-phase, compared with the neat iPP, the existence of MWCNTs can promote the nucleation of γ-phase, leading to the formation of γ-crystal with thicker lamellae. If iPP/MWCNTs solidified in mesophase, MWCNTs can decrease the growth rate of the nodular structure, leading to the formation of mesophase with smaller nodular domains (about 9.4 nm). Mechanical tests reveal that, γ-iPP/MWCNTs composites prepared by slow pressurization display high Young’s modulus, high yield strength and high elongation at break, and meso-iPP/MWCNTs samples have excellent deformability because of the existence of nodular morphology. In this sense, the pressurization method is proved to be an efficient approach to regulate the crystalline structure and the properties of iPP/MWCNTs composites. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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16 pages, 5197 KiB

Open AccessEditor’s ChoiceArticle

Unveiling Temporal Nonlinear Structure–Rheology Relationships under Dynamic Shearing

by Johnny Ching-Wei Lee, Lionel Porcar and Simon A. Rogers

Polymers 2019, 11(7), 1189; https://doi.org/10.3390/polym11071189 - 16 Jul 2019

Cited by 27 | Viewed by 7557

Abstract

Understanding how microscopic rearrangements manifest in macroscopic flow responses is one of the central goals of nonlinear rheological studies. Using the sequence-of-physical-processes framework, we present a natural 3D structure–rheology space that temporally correlates the structural and nonlinear viscoelastic parameters. Exploiting the rheo-small-angle neutron [...] Read more.

Understanding how microscopic rearrangements manifest in macroscopic flow responses is one of the central goals of nonlinear rheological studies. Using the sequence-of-physical-processes framework, we present a natural 3D structure–rheology space that temporally correlates the structural and nonlinear viscoelastic parameters. Exploiting the rheo-small-angle neutron scattering (rheo-SANS) techniques, we demonstrate the use of the framework with a model system of polymer-like micelles (PLMs), where we unveil a sequence of microscopic events that micelles experience under dynamic shearing across a range of frequencies. The least-aligned state of the PLMs is observed to migrate from the total strain extreme toward zero strain with increasing frequency. Our proposed 3D space is generic, and can be equally applied to other soft materials under any sort of deformation, such as startup shear or uniaxial extension. This work therefore provides a natural approach for researchers to study complex out-of-equilibrium structure–rheology relationships of soft materials. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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18 pages, 4456 KiB

Open AccessArticle

Tie-Bar Elongation Based Filling-To-Packing Switchover Control and Prediction of Injection Molding Quality

by Jian-Yu Chen, Chun-Ying Liu and Ming-Shyan Huang

Polymers 2019, 11(7), 1168; https://doi.org/10.3390/polym11071168 - 9 Jul 2019

Cited by 21 | Viewed by 7511

Abstract

Filling-to-packing switchover (also called V/P switchover) is critical for assuring injection molding quality. An improper V/P switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance a consistent molding quality, [...] Read more.

Filling-to-packing switchover (also called V/P switchover) is critical for assuring injection molding quality. An improper V/P switchover setting may result in various defects of injection-molded parts, such as excessive residual stress, flash, short shot, and warpage, etc. To enhance a consistent molding quality, recent V/P switchover approaches adopt cavity pressure profiles requiring sensors embedded in mold cavities, which is invasive to mold cavities and more expensive. Instead of using cavity pressure sensors, by working with the most popular screw position switchover control, this study hereby proposes a novel approach of tuning V/P switchover timing using a tie-bar elongation profile. In this investigation, a dumbbell testing specimen mold is applied to verify the feasibility of the method proposed. The results show that the mold filling and packing stages can be observed along the tie-bar elongation profile, detected by mounting strain gauges on the tie bars. Also, the characteristics of the cavity pressure are similar to those of the tie-bar elongation profile under a proper clamping force condition. Moreover, the varying process parameter settings which include injection speed, V/P switchover point, and holding pressure, can be reflected in these profiles. By extracting their characteristics, the application of the V/P switchover is proved to be realistic. This research conducted an experiment to verify the proposed V/P switchover decision method based on the tie-bar elongation profile. The result showed that the fluctuation of the part’s weight corresponding to a slight change of the barrel’s temperature from 210 °C to 215 °C can be successfully controlled with this method. Besides, the maximum clamping force increment extracted from the tie-bar elongation profile was found to be a good indicator for online monitoring of the reground material variation. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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10 pages, 3845 KiB

Open AccessArticle

Preparation, Structure and Properties of Acid Aqueous Solution Plasticized Thermoplastic Chitosan

by Yu Zhang, Biao-Lan Liu, Liang-Jie Wang, Ying-Hua Deng, Shi-Yi Zhou and Ji-Wen Feng

Polymers 2019, 11(5), 818; https://doi.org/10.3390/polym11050818 - 7 May 2019

Cited by 35 | Viewed by 6155

Abstract

This work provides a simple method for the preparation of thermoplastic chitosan using the most common dilute inorganic and organic acids in aqueous solutions, namely hydrochloric acid (HCl) and acetic acid (HAc). The melting plasticization behavior of chitosan under different concentrations and types [...] Read more.

This work provides a simple method for the preparation of thermoplastic chitosan using the most common dilute inorganic and organic acids in aqueous solutions, namely hydrochloric acid (HCl) and acetic acid (HAc). The melting plasticization behavior of chitosan under different concentrations and types of acid solution was investigated. By means of infrared spectra (IR), scanning electron microscope (SEM), X-ray diffraction (XRD), and other characterization methods, as well as a mechanical property test, it was found that as the acid solution concentration increased, the protonation effect was stronger and the plasticization performance showed a better trend. The structure and performance of the modified chitosan were optimal when the concentration of HCl was around 8 wt %. In addition, it was found that HCl had a better effect on the plasticization of chitosan than HAc, which was because the protonation ability of HCl was stronger than that of HAc. Unlike the casting method, the structure and properties of chitosan sheets prepared by thermoplastic processing were directly affected by protonation, however not by the interaction of anionic-cationic electrostatic attractions between the –NH³⁺ groups of chitosan chains and the carboxyl groups of acetic acids or the chloridoid groups of hydrochloric acid. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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14 pages, 6097 KiB

Open AccessArticle

Preparation Methods of Polypropylene/Nano-Silica/Styrene-Ethylene-Butylene-Styrene Composite and Its Effect on Electrical Properties

by Mingze Gao, Jiaming Yang, Hong Zhao, Hui He, Ming Hu and Shuhong Xie

Polymers 2019, 11(5), 797; https://doi.org/10.3390/polym11050797 - 4 May 2019

Cited by 21 | Viewed by 4209

Abstract

Compared with traditional insulation materials, such as cross-linked polyethylene (XLPE), polypropylene (PP) is famous for its better recyclable and thermal properties, as well as its good electrical performance. However, the problem of poor impact strength has restricted the application of pure PP in [...] Read more.

Compared with traditional insulation materials, such as cross-linked polyethylene (XLPE), polypropylene (PP) is famous for its better recyclable and thermal properties, as well as its good electrical performance. However, the problem of poor impact strength has restricted the application of pure PP in high-voltage, direct current (HVDC) cables. In this paper, styrene-ethylene-butylene-styrene block copolymer (SEBS) was used as a toughening filler, and nano-SiO₂ was expected to improve the electric properties of the nano-composite. By controlling the masterbatch system, the dispersion characteristics of nano-SiO₂ in the ternary composite system were changed. When PP/SiO₂ was used as the masterbatch and then blended with SEBS, nano-SiO₂ tended to disperse in the PP phase, and the number of nano-particles in the SEBS phase was lower. When PP/SEBS was used as the masterbatch, nano-SiO₂ was distributed in both the PP phase and the SEBS phase. When SEBS/SiO₂ was used as the masterbatch, nano-SiO₂ tended to be dispersed in the SEBS phase. The different dispersion characteristics of nano-SiO₂ changed the crystallization and mechanical properties of the ternary composite system and produced different electrical performance improvement effects. The results of our experiment revealed that the space charge suppression capability was positively correlated with the direct current (DC) breakdown strength improvement effect. Compared with the DC performance of 500 kV commercial XLPE materials, the self-made PP-based ternary composite system has better space charge suppression effects and higher DC breakdown strength. When nano-SiO₂ was more dispersed in the PP phase, the space charge improvement effect was best. When the nano-SiO₂ particles were more dispersed in the SEBS phase, the expected electrical property improvement was not obtained. Scanning electron microscopy showed that the nano-SiO₂ particles in the SEBS phase were more dispersed at the interface than in the SEBS matrix, indicating that the nano-particles were poorly dispersed, which may be a reason why the electrical properties of the composite system were not significantly improved. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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11 pages, 8596 KiB

Open AccessArticle

High Capacity Nano-Sized Carbon Spheres for Lithium-Ion Battery Anode Materials

by Youliang Wang, Guoyun Yu, Xiujuan Chen and Ansong Wang

Polymers 2019, 11(4), 645; https://doi.org/10.3390/polym11040645 - 9 Apr 2019

Cited by 6 | Viewed by 4158

Abstract

A one-step hydrothermal method is reported for synthesizing carbon spheres (Cs) with sucrose as the carbon resource for the anode materials in lithium-ion batteries (LIBs). Firstly, the influences of synthesis temperature and time on particle size and the morphology of the Cs were [...] Read more.

A one-step hydrothermal method is reported for synthesizing carbon spheres (Cs) with sucrose as the carbon resource for the anode materials in lithium-ion batteries (LIBs). Firstly, the influences of synthesis temperature and time on particle size and the morphology of the Cs were researched. Then, modified carbon spheres (MCs) were synthesized with some surfactants, such as hexadecyl trimethyl ammonium bromide (CTAB) and polyvinyl alcohol (PVA). Finally, nano-sized MCs with an average diameter of 70 nm, owning the smooth surface and uniform spherical morphology systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The outstanding performances of nano-sized MCs synthesized with PVA were demonstrated as anode materials in LIBs. The higher initial discharge capacity of 1180 mAhg⁻¹ and the excellent discharge capacity of 470 mAhg⁻¹ were obtained respectively at 100 mAg⁻¹ (0.27 C) over 50 cycles. The nano-sized MCs has also shown remarkable performance of rate capability of 284.6 mAhg⁻¹ at 1.5 C. In addition, the cycling reversibility of the nano-sized MCs is more stable than that of the sub-micron sized MCs modified with CTAB and no surfactant respectively. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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14 pages, 12974 KiB

Open AccessArticle

Molecular Dynamics Simulation on the Effect of Bonding Pressure on Thermal Bonding of Polymer Microfluidic Chip

by Mingyong Zhou, Xiang Xiong, Dietmar Drummer and Bingyan Jiang

Polymers 2019, 11(3), 557; https://doi.org/10.3390/polym11030557 - 24 Mar 2019

Cited by 18 | Viewed by 6253

Abstract

Thermal bonding technology is the most commonly used approach in bonding injection-molded microfluidic chips. Although the bonding mechanism is still under debate, the molecular dynamics (MD) method can provide insight into the bonding process on a macromolecular level. In this study, MD simulations [...] Read more.

Thermal bonding technology is the most commonly used approach in bonding injection-molded microfluidic chips. Although the bonding mechanism is still under debate, the molecular dynamics (MD) method can provide insight into the bonding process on a macromolecular level. In this study, MD simulations for thermal bonding of PMMA substrate and cover sheet were performed. The molecule configuration and density distribution during the thermal bonding process were studied. The effects of bonding pressure on the equivalent strain, joining energy and diffusion coefficient were investigated. The debonding process was simulated to analyze the bonding strength and failure mechanism. Simulation results show that penetration mainly takes place near the interface area. Although the final density increases slightly with increasing pressure, the bonding interface is still insufficiently filled. The equivalent strain grows faster than that in the later stage because of the gap at the interface. The bonding pressure shows clear effects on the joining energy, diffusion coefficient and stress–strain behavior. Tensile failure occurs at the interface, with PMMA chains stretched between two layers. The majority of the change in potential energy is correlated with the change in non-bonded energy. At yield strain, the low-density defect at the interface weakens the tensile strength of bonded chip. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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14 pages, 9245 KiB

Open AccessArticle

Molecular Dynamics Study on the Deformation Behaviors of Nanostructures in the Demolding Process of Micro-Injection Molding

by Can Weng, Jin Yang, Dongjiao Yang and Bingyan Jiang

Polymers 2019, 11(3), 470; https://doi.org/10.3390/polym11030470 - 12 Mar 2019

Cited by 13 | Viewed by 3849

Abstract

Polymer parts with nanostructures have broad applications, possessing excellent optical, electrochemical, biological, and other functions. Injection molding technology is one of the main methods for mass production of polymer parts with various shapes and sizes. The demolding process is vital to the replication [...] Read more.

Polymer parts with nanostructures have broad applications, possessing excellent optical, electrochemical, biological, and other functions. Injection molding technology is one of the main methods for mass production of polymer parts with various shapes and sizes. The demolding process is vital to the replication quality of molded parts with nanostructures. For this study, molecular dynamics simulations of polypropylene (PP), polymethyl methacrylate (PMMA), and cycloolefin copolymer (COC) were conducted for the demolding process. The average velocity, density distribution, adhesion energy, and demolding resistance were introduced to analyze the deformation behaviors of polymer nanostructure from a nickel nano-cavity with an aspect ratio of 2:1. The shoulders of nanostructures were firstly separated from the nickel mold insert in the simulation. Under the external demolding force of 0.07 nN, PP and PMMA could be successfully demolded with some deformations, while COC could not be completely demolded due to the greater adhesion energy between COC and Ni. It was found that the maximum adhesion energy occurred in the separation process between the shoulder of the nanostructure and Ni and the huge adhesion energy was the main cause of demolding defects. The velocity difference of the whole polymer layer and polymer nanostructure was further analyzed to explain the nanostructure deformation. In order to improve the quality of demolding, the external force applied on polymers should be properly increased. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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15 pages, 5699 KiB

Open AccessEditor’s ChoiceArticle

Mechanical and Water-Resistant Properties of Eco-Friendly Chitosan Membrane Reinforced with Cellulose Nanocrystals

by Haiquan Mao, Chun Wei, Yongyang Gong, Shiqi Wang and Wenwen Ding

Polymers 2019, 11(1), 166; https://doi.org/10.3390/polym11010166 - 18 Jan 2019

Cited by 77 | Viewed by 9473

Abstract

Environmentally benign and biodegradable chitosan (CS) membranes have disadvantages such as low mechanical strength, high brittleness, poor heat resistance and poor water resistance, which limit their applications. In this paper, home-made cellulose nanocrystals (CNC) were added to CS to prepare CNC/CS composite membranes [...] Read more.

Environmentally benign and biodegradable chitosan (CS) membranes have disadvantages such as low mechanical strength, high brittleness, poor heat resistance and poor water resistance, which limit their applications. In this paper, home-made cellulose nanocrystals (CNC) were added to CS to prepare CNC/CS composite membranes through mechanical mixing and solution casting approaches. The effects of CNC dispersion patterns and CNC contents on the properties of composite membranes were studied. The analysis of the surface and cross-section morphology of the membranes showed that the dispersion performance of the composite membrane was better in the case that CNC was dissolved in an acetic acid solution and then mixed with chitosan by a homogenizer (Method 2). CNC had a great length-diameter ratio and CNC intensely interacted with CS. The mechanical properties of the composite membrane prepared with Method 2 were better. With a CNC content of 3%, the tensile strength of the composite membrane reached 43.0 MPa, 13.2% higher than that of the CNC-free membrane. The elongation at break was 41.6%, 56.4% higher than that of the CNC-free membrane. Thermogravimetric, contact angle and swelling analysis results showed that the addition of CNC could improve the heat and water resistance of the chitosan membrane. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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12 pages, 2897 KiB

Open AccessArticle

Fabrication of Reactive Poly(Phenyl-Substituted Siloxanes/Silsesquioxanes) with Si‒H and Alkoxy Functional Groups via the Piers–Rubinsztajn Reaction

by Minghao Yi, Xunjun Chen, Shufang Wu, Jianfang Ge, Xinhua Zhou and Guoqiang Yin

Polymers 2018, 10(9), 1006; https://doi.org/10.3390/polym10091006 - 10 Sep 2018

Cited by 15 | Viewed by 4166

Abstract

Poly(phenyl-substituted siloxanes/silsesquioxanes) are obtained by the Piers–Rubinsztajn (PR) reaction of hydrogen-containing siloxanes (HCS) with diphenyldialkoxysilanes such as diphenyldimethoxysilane and diphenyldiethoxysilane catalyzed by tris(pentafluorophenyl)borane. ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography, and refractive index analysis revealed that apart from phenyl substituents [...] Read more.

Poly(phenyl-substituted siloxanes/silsesquioxanes) are obtained by the Piers–Rubinsztajn (PR) reaction of hydrogen-containing siloxanes (HCS) with diphenyldialkoxysilanes such as diphenyldimethoxysilane and diphenyldiethoxysilane catalyzed by tris(pentafluorophenyl)borane. ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography, and refractive index analysis revealed that apart from phenyl substituents and complex structures such as molecular bridges composed of D₂^Ph2[(C₆H₅)₂Si(OSi)₂], structures also existed in these polymers, having high refractive indexes (above 1.50) and high molecular weights (75.60 KDa·mol⁻¹). As revealed by thermogravimetric analysis, these polymers have high thermal stability as well, with temperature at 5% mass loss (T_5%) increasing by 182.5 °C and R_w (residual weight ratio) increasing by 5.17 times from 14.63% to 75.60%, as compared to HCS, exhibiting its potential application as resins for resisting strong heat. Such high-refractive-index and temperature-resistant poly(phenyl-substituted siloxanes/silsesquioxanes) with Si–H and alkoxy functional groups can be used as a good addition-type crosslinking agent with adhesion-promoting properties or a special curing agent that can solidify silicone materials through simultaneous addition and condensation reactions, which has potential application in the light-emitting diode (LED) packaging industry. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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26 pages, 7328 KiB

Open AccessEditor’s ChoiceReview

Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

by Jianhui Qiu, Guohong Zhang, Eiichi Sakai, Wendi Liu and Limin Zang

Polymers 2020, 12(4), 759; https://doi.org/10.3390/polym12040759 - 31 Mar 2020

Cited by 28 | Viewed by 6900

Abstract

Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding [...] Read more.

Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding between the two dissimilar materials compared with the traditional USW. This review focused on the advances of applying the ultrasonic TWTP for thermoplastic materials. The research development on the ultrasonic TWTP of polycarbonate (PC) and polymethyl methacrylate (PMMA), polylactic acid (PLA) and polyformaldehyde (POM), and PLA and PMMA are summarized according to the preparation of the third phase, welded strength, morphologies of rupture surfaces, thermal stability, and others. The review aimed at providing guidance for using ultrasonic TWTP in polymers and a basic understanding of the welding mechanism, i.e., interdiffusion and molecular motion mechanisms between the phases. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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20 pages, 4717 KiB

Open AccessReview

A Review on Styrene Substitutes in Thermosets and Their Composites

by Yuchao Wu, Mingen Fei, Renhui Qiu, Wendi Liu and Jianhui Qiu

Polymers 2019, 11(11), 1815; https://doi.org/10.3390/polym11111815 - 5 Nov 2019

Cited by 35 | Viewed by 9082

Abstract

In recent decades, tremendous interest and technological development have been poured into thermosets and their composites. The thermosets and composites with unsaturated double bonds curing system are especially concerned due to their versatility. To further exploit such resins, reactive diluents (RDs) with unsaturated [...] Read more.

In recent decades, tremendous interest and technological development have been poured into thermosets and their composites. The thermosets and composites with unsaturated double bonds curing system are especially concerned due to their versatility. To further exploit such resins, reactive diluents (RDs) with unsaturated sites are usually incorporated to improve their processability and mechanical properties. Traditional RD, styrene, is a toxic volatile organic compound and one of the anticipated carcinogens warned by the National Institute of Health, USA. Most efforts have been conducted on reducing the usage of styrene in the production of thermosets and their composites, while very few works have systematically summarized these literatures. Herein, recent developments regarding styrene substitutes in thermosets and their composites are reviewed. Potential styrene alternatives, such as vinyl derivatives of benzene and (methyl)acrylates are discussed in details. Emphasis is focused on the strategies on developing novel RD monomers through grafting unsaturated functional groups on renewable feedstocks such as carbohydrates, lignin, and fatty acids. This review also highlights the development and characteristics of RD monomers and their influence on processability and mechanical performance of the resulting thermosets and composites. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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24 pages, 8871 KiB

Open AccessReview

Ultrasonic Molding Technology: Recent Advances and Potential Applications in the Medical Industry

by Ulisses Heredia-Rivera, Inés Ferrer and Elisa Vázquez

Polymers 2019, 11(4), 667; https://doi.org/10.3390/polym11040667 - 11 Apr 2019

Cited by 31 | Viewed by 10390

Abstract

Recently, ultrasonic molding (USM) has emerged as a promising replication technique for low and medium volume production of miniature and micro-scale parts. In a relatively short time cycle, ultrasonic molding can process a wide variety of polymeric materials without any noticeable thermal degradation [...] Read more.

Recently, ultrasonic molding (USM) has emerged as a promising replication technique for low and medium volume production of miniature and micro-scale parts. In a relatively short time cycle, ultrasonic molding can process a wide variety of polymeric materials without any noticeable thermal degradation into cost-effective molded parts. This research work reviews recent breakthroughs of the ultrasonic injection molding and ultrasonic compression molding process regarding the equipment and tooling development, materials processing and potential applications in the medical industry. The discussion is centered on the challenges of industrializing this technology, pointing out the need for improvement of the current process’s robustness and repeatability. Among the most important research areas that were identified are the processing of novel engineered and nanomaterials, the understanding and control of the ultrasonic plasticization process and the tooling and equipment development. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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