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Article

Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane

by
Da-Sheng Zhang
1,
Xiao-Hua Gu
1,2,3,*,
Si-Wen Liu
4,
Yan Liu
2,
Qing-Yun Zhou
1,
Shang-Wen Zhu
2 and
Yan-Wei Zhu
3
1
School of Material Science and Engineering of Qiqihar University, Qiqihar 161006, China
2
School of Energy and Building Environment of Guilin University of Aerospace Technology, Guilin 541004, China
3
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China
4
College of Innovative Material & Energy, Hubei University, Wuhan 430062, China
*
Author to whom correspondence should be addressed.
Sustainability 2022, 14(23), 15685; https://doi.org/10.3390/su142315685
Submission received: 14 October 2022 / Revised: 15 November 2022 / Accepted: 21 November 2022 / Published: 25 November 2022
(This article belongs to the Topic Clean and Low Carbon Energy)
Browse Figures
Versions Notes

Abstract

:
Polyurethane (PU) has become one of the most widely used materials in the industrial field due to its excellent performance and wide range of applications. The increasing consumption of polyurethane materials has resulted in significant polyurethane waste. We can recycle waste polyurethane to obtain recycled polyurethane, but to make the recycled polyurethane meet different performance requirements in terms of utility and cost and enable the recycled polyether polyol to be further applied to high-end applications, it is necessary to improve the use value of recycled polyether polyol. In this paper, self-made Fluorodiol was added to the degradation process of waste polyurethane to obtain fluorinated regenerated polyether polyol. Recycled fluorinated polyurethane with excellent performance was prepared using fluorine-containing recycled polyether polyol. The regenerated fluorinated polyether polyols were characterized by infrared spectroscopy, viscosity, hydroxyl value, and GPC molecular weight distribution. The density, apparent morphology, water absorption, mechanical strength, thermal conductivity, and thermal stability of RFPU rigid foams with different fluorine contents were studied by scanning electron microscopy. The results show that when the addition of Fluorodiol was 8% of the mass of waste polyurethane, the density was 41.2 kg/m3, the immersion loss rate was 2.125%, the compressive strength was 0.315 Mpa, and the thermal conductivity was 0.0227 W/m·K. The RFPU prepared by Fluorodiol has low surface energy, good compressive strength, hydrolysis resistance, and is expected to be widely used in special insulation materials. Thus, the sustainable recycling of polyurethane is achieved.

1. Introduction

Polyurethane (PU) is a polymer with a carbamate segment repeating structural unit prepared by an isocyanate and polyol reaction. Polyurethane is now one of the most widely used materials. Polyurethane foam, which accounts for up to 80% of the polyurethane industry, has been widely used in various industries, including building and refrigerator insulation, car seats, and cushions [1,2,3,4]. Due to the continuous increase in the consumption of polyurethane materials, a large amount of waste polyurethane has accumulated. However, due to the excellent stability of polyurethane, the material is not easily degraded by microorganisms or air under natural conditions; it is insoluble, and it is difficult to treat [5,6,7,8,9]. Moreover, more and more states explicitly prohibit its burial or incineration, and it is difficult to recycle, resulting in a waste of living space and chemical resources [1,4,10,11,12,13,14]. Therefore, how to deal with the degradation and reuse of waste PU in a green and efficient manner is crucial to determine [15,16,17,18]. The recycling prospect of waste polyurethane is very broad and has great potential research value and significance.
Fluorinated polyurethane is a polymer material with special functions. Since Lovelace invented the first fluorine-containing polyurethane patent in 1958, the synthesis of fluorine-containing polyurethane has attracted widespread attention and become a popular topic of polyurethane research [11,19,20,21,22,23,24]. In this paper, by including fluorine-containing groups in the degradation process of waste polyurethane, fluorine-containing recycled polyols were prepared and then foamed to prepare fluorine-containing polyurethane rigid foam, which combines the excellent mechanical properties and surface properties of polyurethane and fluorine-containing polymers, giving the material high strength, high thermal stability, high thermal insulation performance, and excellent hydrophobicity and oil resistance [13,20,25,26,27,28]. In this paper, a series of fluorine-containing polyurethane rigid foams were prepared using fluorine-containing recycled polyols obtained from the degradation of waste polyurethane foams by ethylene glycol (EG) and diethylene glycol (DEG) composite Fluorodiols as raw materials, and their properties and composition were characterized. This modification method has no relevant literature in the field of waste polyurethane high-value recycling. This method can help realize low energy consumption, low cost, rapid recovery, and high-value utilization of waste polyurethane. This method can explore the sustainability of polyurethane to contribute to the protection of the environment, and is of great significance to the industrial production of waste polyurethane degradation and recovery.

2. Materials and Methods

2.1. Reagents and Apparatus

Waste PU rigid foam, waste directly buried pipe polyurethane foam, Shandong Haier Group, Qingdao, China; ethylene glycol (EG): purity 98%, China Nanjing Gaohua Chemical Group Co., Ltd., Nanjing, China; diethylene glycol (DEG): purity 98%, China Shandong Huasheng Chemical Co., Ltd., Zhanhua, China; isophorone diisocyanate (IPDI): industrial grade, China Shandong Lianchuang Chemical Co., Ltd. Qingdao, China, KOH, purity 98%, China Beijing Kono Chemical Co., Ltd., Beijing, China; double metal catalyst (DMC), industrial grade, China Changzhou Hongyu Chemical Co., Ltd., Changzhou, China; polyether polyol 4110, industrial grade, China Shandong Yinuowei Chemical Co., Ltd., Zibo, China; 4,4′-diphenylmethane diisocyanate (MDI), industrial grade, China Shandong Vanke New Materials Co., Ltd., Dongying, China; organic tin, industrial grade, China Pharmaceutical Shanghai Chemical Reagent Company, Shanghai, China; dimethyl silicone oil, analytically pure, China Shandong Yinuowei Chemical Co., Ltd., Zibo, China; foaming agent Cyclopentane, industrial grade, China Pharmaceutical Shanghai Chemical Reagent Co., Ltd., Shanghai, China; Fluoroalcohol (C8, 35.16%; C10, 53.31%), molecular weight 486, China Yangzhou Modier Electronic Materials Co., Ltd., Yangzhou, China; diethanolamine (DEA), analytically pure; ethyl acetate, analytically pure, Aladdin reagent; toluene, analytically pure, Aladdin reagent.

2.2. Sample Preparation

2.2.1. Fluorodiol Preparation

The first reactor with a thermometer and stirring device was cleaned with nitrogen, and nitrogen was continuously introduced during the reaction. Ethyl acetate and IPDI (2) were added to the first reactor, stirred, and heated to 60 °C until IPDI was completely dissolved. Fluoroalcohol (1) was slowly added to the reactor. After the addition, the reactor was heated to 80 °C for 3 h to obtain perfluoroalkyl isocyanate (3).
The second reactor with a thermometer and stirring device was cleaned with nitrogen, and nitrogen was continuously introduced during the reaction. Ethyl acetate and diethanolamine (4) were added to the second reaction kettle and stirred at 10 °C. After the diethanolamine was completely dissolved, the temperature was increased to 20 °C. The product (3) was dropped into the diethanolamine solution, and the system’s temperature was kept below 20 °C during the dropping process. After the addition, the reactor temperature was raised to 25 °C for 2 h. After the reaction, toluene was added to the final reaction system for washing, filtering, and drying, and finally, the Fluorodiol product (5) was obtained. The reaction process is shown in Figure 1.

2.2.2. RFPU Sample Preparation

A total of 50 g waste polyurethane foam was cleaned, dried, and then broken into 1~2 mm powder, which was waste polyurethane powder; fluoroglycol and two-component decomposition crosslinking agents (EG as alcoholysis agent, DEG as alcoholysis agent), catalyst KOH, and DMC were added to the reactor, stirred, and dissolved at 130 °C. After dissolution, 100 g of waste polyurethane powder was added. The temperature was increased to 200 °C for alcoholysis reaction for 2 h, then cooled to room temperature to obtain fluorinated regenerated polyether polyol. The ratio of the mass of waste polyurethane powder to the total mass of Fluorodiol, two-component decomposition crosslinking agent and catalyst is 1:1.2. Five parallel samples with different fluorine contents were prepared, and the addition of Fluorodiol was 2%, 4%, 6%, 8%, and 10% of the mass of waste polyurethane. Figure 2 shows the mechanism of the degradation reaction [4,29,30,31,32].
Take 20 g fluorine-containing recycled polyether polyol and 20 g polyether polyol 4110 obtained by the above steps: add silicone oil L-600, organotin catalyst, and foaming agent Cyclopentane in turn; stir well; add 45 g MDI; stir quickly; and let stand to allow it to foam naturally to create the fluorine-containing recycled polyurethane material. Figure 3 shows the schematic formula for preparing the RFPU.

2.2.3. Reused Rigid Polyurethane Foam (RRPU) Sample Preparation

The steps of treating waste polyurethane foam are the same as those of RFPU. The two-component decomposition crosslinking agent (EG as alcoholysis agent, DEG as alcoholysis agent), KOH, and DMC were added to the reactor and stirred at 130 °C. After dissolution, 100 g of waste polyurethane powder was added, and the temperature was raised to 200 °C for an alcoholysis reaction for 2 h and cooled to room temperature to obtain recycled polyether polyol. The mass ratio of waste polyurethane powder to the total mass of the two-component decomposition crosslinking agent and catalyst is 1:1.2; the foaming step is the same as that of RFPU, resulting in RRPU.

2.2.4. Fluoroalcohol Comparison Samples

The steps of treating waste polyurethane foam are the same as those of RFPU. A total of 8 g of fluoroalcohol and two-component decomposition crosslinking agent (EG as alcoholysis agent, DEG as alcoholysis agent), KOH catalyst, and DMC were added to the reactor, stirred, and dissolved at 130 °C. After dissolution, 100 g of waste polyurethane powder was added, the temperature was raised to 200 °C for an alcoholysis reaction for 2 h, and the sample was then cooled to room temperature to obtain recycled polyether polyol. The mass ratio of waste polyurethane powder to the total mass of the two-component decomposition crosslinking agent and catalyst is 1:1.2. The foaming step is the same as the RFPU foaming step, resulting in fluoroalcohol comparison samples.

2.2.5. Prue 4100 Sample Preparation

The pure 4100 sample is obtained by following this process: take 40 g of the above steps to obtain the polyether polyol 4110; add silicone oil L-600, organotin catalyst, and foaming agent Cyclopentane; stir evenly; add 45 g MDI; quickly stir; and stand to allow natural foaming.

2.3. Characterization

The infrared spectra of the prepared Fluorodiol, regenerated fluorinated polyether polyol, and RFPU were analyzed using a Fourier transform infrared spectrometer (IR-960, China Tianjin Rui’an Technology Co., Ltd., Tianjin, China).
Use the ‘GB/T12008.7-2010’ test viscosity method under the experimental conditions of 25 degrees Celsius with an NDJ-1 rotary viscometer to measure the viscosity of fluorinated polyether polyol products.
The GPC molecular weight distribution test was carried out by taking 5 mg of fluorine-containing polyether polyol in a sample bottle and adding 2 mL of spectral-grade N-N dimethylamide.
The hydroxyl value of fluorinated polyether polyol was determined by acid–base titration.
The prepared foam was cut into 50 mm × 50 mm × 50 mm samples, and the compressive strength of the samples at 10% deformation was tested using a material universal testing machine (WSM20KN, China Changchun Intelligent Equipment Co., Ltd., Changchun, China).
The regenerated RFPU rigid foam was cut into thin samples, and the cell of the RFPU structure was observed by scanning electron microscopy (KYKY-EM3900, China Guangzhou Hongsheng Technology Co., Ltd., Guangzhou, China). The sample was prepared into a square of 1 cm × 1 cm × 1 cm. The sample was completely immersed in water for 24 h, and the water-absorption rate was measured. After the sample was completely dried, the immersion loss rate was measured.
Thermogravimetric analysis of recycled PU rigid foam was carried out using a thermogravimetric analyzer (Q5000IR, TA, New Castle County, DE, USA).
The thermal conductivity of recycled PU rigid foam at 25 °C was measured using a thermal conductivity meter (DRPL-III, China Shanghai Jiezhun Instrument Equipment Co., Ltd., Shanghai, China).

3. Results and Discussion

3.1. FTIR Spectra Analysis

3.1.1. FTIR Spectra Analysis of Fluorodiol

Figure 4 shows the FTIR spectra of Fluoroalcohol and Fluorodiol. For Fluoroalcohol, the absorption peak at 3600–2000 cm−1 belongs to the stretching vibration of −OH, and the absorption peak at 1242 cm−1,1320 cm−1 should be attributed to the stretching vibration of C−F [25,33]. Compared with the Fluorodiol, the new absorption peaks at 1726 cm−1 and 1464 cm−1 correspond to the stretching vibration of C=O and C−N in −NCO [34]. Therefore, it can be concluded that the dihydroxy group has been successfully applied to Fluoroalcohol.

3.1.2. FTIR Spectra Analysis of Fluorinated Regenerated Polyols

It can be seen in Figure 5 that compared with the other three curves (b, c, d), the polyether polyol 4110 (a) has a strong absorption band in the range of 3500–3300 cm−1, which is the stretching vibration peak of the alcohol hydroxyl group. A clear, strong absorption band near 1082 cm−1 is attributed to the stretching vibration peak of the polyether polyurethane ether group. It can be concluded that the degradation product is a mixture of polyether polyols and aromatic polyols [5,12,35,36,37]. The vibration absorption peaks of −C−F near 1180 cm−1 and 1128 cm−1 can be found on curves c and d, and the saturated vibration absorption peak of Sustainability 14 15685 i001 is found at 1352 cm−1.
It can be seen in Figure 5 that the Fluorodiol synthesized in this paper is consistent with the product structure in the synthesis path. The curves of four kinds of degradation strips showed strong absorption bands in the range of 3500–3300 cm−1, which were the stretching vibration peaks of the alcohol hydroxyl groups. The strong absorption band near 1740 cm−1 is the benzene overtone peak. A clear, strong absorption band near 1082 cm−1 is attributed to the stretching vibration peak of the polyether polyurethane ether group [3,29,38,39,40]. It can be concluded that the degradation product is a mixture of fluorinated polyether polyols and fluorinated aromatic polyols.

3.2. Viscosity Analysis of Regenerated Polyol

It is known that the lower the viscosity of the degraded material obtained after the alcoholysis of waste polyurethane, the more thorough the degradation and the higher the hydroxyl value. The data in Figure 6 show that with the addition of Fluorodiols, the viscosity of the degraded material will increase, and the hydroxyl value will decrease, which is not expected. When the addition of Fluorodiol reaches 11%, the viscosity is greatly increased to 3653.2 mPa· s, at which cannot be foamed at room temperature; the hydroxyl value also decreased significantly to 352.5 mg KOH/g, indicating that the waste polyurethane was not fully degraded to form small molecular alcohols. This situation is due to the fact that the addition of Fluorodiols hindered the degradation of waste polyurethane so that it was not fully degraded; meanwhile, the degradation of a large number of unreacted carbamate bonds led to an increase in viscosity and hydroxyl value decline.

3.3. GPC Analysis of Regenerated Polyol

The molecular weight test of regenerated polyols with different amounts of Fluorodiol gradients yielded the following data, as Table 1:
The polyurethane chain is decomposed into low-molecular-weight segments due to the alcoholysis agent and catalyst, and its elution time is similar to that of polyether polyol 4110, which is an oligomer. The average molecular weight (Mn) of the recovered polyols was between 4804 and 2465. With the increase in the amount of Fluorodiol, the molecular weight gradually increased, and the elution time gradually decreased. When the addition of Fluorodiol exceeded 8%, the changes in Mn and PDI of recovered polyols increased significantly. This shows that the maximum Fluorodiol amount that can be used when the molecular weight distribution of the prepared fluorine-containing recycled polyol is the most uniform is 8%, which ensures that the waste polyurethane is degraded as fully as possible.

3.4. The Effect of Fluorodiol on the Density of RFPU Rigid Foams

The densities of RFPUs prepared with different amounts of Fluorodiol were measured using the pycnometer method. The results are shown in Figure 7. The results showed that the foam density did not increase significantly with the increase in the amount of Fluorodiol from 0 to 8%, and the foam density was 41.2 kg/m3 when the amount was 8%. When the amount of Fluorodiol reached 10%, the excessive fluorine content in the polyurethane foaming process produced many defoaming phenomena, making the final density soar to 72.4 kg/m3.

3.5. Effect of Fluorodiols on Water Absorption and Loss Rate of RFPU Foam

The effect of different amounts of Fluorodiol on the water absorption of RFPU was studied by measuring the water absorption. First, RFPU was made into a sample with a volume of 1 cm3 and then put into deionized water. The water-absorption rate of RFPU with different Fluorodiol amounts was calculated by measuring the mass of the sample before and after immersion. The results are shown in Figure 8.
It can be seen in Figure 8 that the water-absorption decreases with the increase in the amount of Fluorodiol. This is because the fluorine atoms in the Fluorodiol are distributed in a spiral shape on the carbon chain, which can protect the polyurethane molecular chain. At the same time, the polarizability of the C−F bond is small, so the chain segment of the fluorine−containing C−F group easily migrates from the inside of the material to the surface, which causes the surface of the RFPU to accumulate a large number of polyurethane segments with low surface energy, making it difficult for water to spread and wet its surface. At the same time, because Fluorodiol has a six-ring structure group, this group can enhance the strength of the polyurethane chain segment, ensure the strength of the pore wall of each polyurethane cell, and protect the relative independence of the cells. For these two reasons, the water absorption of RFPU decreases with the increase in the amount of Fluorodiol.
It can be seen from the experimental results that the water absorption of the RFPU prepared by adding Fluorodiol decreased significantly, and the loss rate of the RFPU soaked in deionized water was determined, as shown in Figure 9.
It can be seen from Figure 9 that the loss rate of the PU rigid foam without Fluorodiol was 8.779%, while the loss of the RFPU was significantly reduced after the addition of Fluorodiol, reaching 2.125% when the amount of Fluorodiol was 8%. Similarly, due to the addition of fluorine-containing groups, the fluorine-containing polyurethane chain segment has a strong shielding effect and stability. The surface energy of the RFPU is significantly reduced and stable.

3.6. Effect of Fluorodiol on the Compressive Strength of RFPU Foam

The effect of different fluoroalcohols on the compressive strength of fluorinated recycled PU rigid foam is shown in Figure 10. In Figure 10, it can be seen that when fluonol is added to the system, the compressive strength of the prepared fluorine-containing recycled polyurethane rigid foam decreases significantly. This is because the monohydric alcohol seals the regenerated polyol and reduces the activity of the regenerated polyol. The reaction of the fluorine-containing recycled polyol during foaming is insufficient, and the generated polyurethane segment is short, so the strength of the fluorine-containing recycled polyurethane rigid foam is significantly reduced.
When Fluorodiol was added to the system, the compressive strength of the prepared fluorine-containing recycled polyurethane rigid foam was significantly improved. When the addition of Fluorodiol was 8%, the strength was the highest, up to 0.315 Mpa. However, when the addition of Fluorodiol reached 10%, the compressive strength of the RFPU decreased significantly because of the incomplete degradation of Fluorodiol. This is because the bond energy of C−F is as high as 485 kJ/mol, which is much larger than that of the C−C bond, which leads to a spiral distribution of adjacent fluorine atoms along the carbon chain, while straight-chain alkanes generally form a zigzag chain configuration. In addition, a rigid six-ring structure was introduced in the synthesis of Fluorodiols, which can greatly improve the rigidity of polyurethane segments. These two structures provide a shielding effect for molecular chain coordination, which reduces the intermolecular force and improves the strength of the chain segment. At the same time, the binding force between the long chains of fluorinated polyurethane is improved, thus improving the compressive strength of the RFPU.

3.7. Analysis of Thermal Conductivity of Fluorine-Containing Recycled Polyurethane

Rigid polyurethane foam is usually used for thermal insulation applications, and thermal conductivity (λ) is a crucial characteristic. The results of the thermal conductivity of regenerated polyurethane prepared from regenerated polyols with different amounts of fluorine and polyurethane prepared using 4110 are shown in Figure 11. The thermal conductivity is related to the apparent density of the foam and the thermal conductivity of the gas is used as the foaming agent. Although the whole foam contains only a small part of the polyurethane matrix, because its λ value is much higher than that of the foaming agent, the foam with higher density often has higher thermal conductivity. Therefore, in a certain range, with the increase in recycled polyols, the thermal conductivity of polyurethane foam increases gradually, and the thermal insulation decreases [41,42,43,44]. For example, the thermal conductivity of polyurethane prepared from recycled polyols from 0.0285 W/m·K to 0.0336 W/m·K showed an increase of 17.9%. When the addition of perfluorinated monohydric alcohol made the polyurethane chain segment shorter, the small cell increased the foam density and decreased the thermal conductivity of the foam, but it still did not reach the level prepared by pure 4110. However, the thermal conductivity decreased significantly after the addition of Fluorodiols. When the content reached 8%, the thermal conductivity reached 0.0227 W/m·K, which was 20.3% lower than pure 4110. This is because the special helical structure of Fluorodiols can make different polyurethane segments more firmly connected and increase the distance between each segment, which makes the polyurethane pore wall thicker and stronger. Such pore walls allow polyurethane foam to have larger cells while maintaining strength.

3.8. SEM Analysis of RFPU

In Figure 12a-1,a-2, it can be seen that the RFPU prepared by Fluoroalcohol has an obvious defoaming phenomenon and skeleton rupture phenomenon. This is due to the end-capping phenomenon of the regenerated polyol produced by Fluoroalcohol during the degradation of waste polyurethane, which leads to an insufficient polymerization reaction in the foaming process. The long chain of polyurethane becomes shorter, and the polyurethane is not crosslinked between the molecular links, resulting in the phenomenon of cracking and skeleton rupture.
Figure 12b-1,b-2 show RFPU with 4% Fluorodiol addition, Figure 12c-1,c-2 show RFPU with 6% Fluorodiol addition, and Figure 12d-1,d-2 show RFPU with 8% Fluorodiol addition. Compared with the RFPU prepared by fluorine-containing monohydric alcohol, it can be seen that the RFPU prepared by Fluorodiol has a more complete cell structure; the cell structure is a regular hexagon, and the skeleton is thick and the crosslinking structure is excellent. Compared with the RFPU prepared by Fluoroalcohol, the cell distribution of RFPU prepared by Fluorodiol is more uniform and denser. This good geometric structure and uniform cell distribution can enable the RFPU to have better compressive strength and lower thermal conductivity.
The fluorinated regenerated PU rigid foam prepared with 8% Fluorodiol has a larger cell structure. The good crosslinking degree of the fluorine-containing recycled PU rigid foam provides higher compressive strength for the foam body and can seal the gas well so that the foam has very good heat-insulation and heat-preservation performance.

3.9. TG Analysis of RFPU

Figure 9 shows the TG curve of the RFPU with different amounts of Fluorodiol. The thermal degradation of the RFPU has two stages: the first stage is caused by the pyrolysis of the hard segment at about 350 °C; the pyrolysis of the soft segment is the cause of the second stage. It is clear that two different degradation steps are involved in Figure 13. The second halves of the two curves are almost identical because RFPUs with different amounts of Fluorodiol have the same soft segment composition. However, the first halves of the two curves are different. With the increase in the amounts of Fluorodiols, the half-decomposition temperature (T1/2) of the RFPU is higher than that of RPU [45,46]. This shows that introducing Fluorodiol as a modifier improves the thermal stability of the hard segment. The thermal stability of the hard segment determines the lower limit of the performance stability of polyurethane foam at high temperatures. Therefore, when improving the thermal stability of polyurethane foam, the modified hard segment is more useful than the modified soft segment [47].

3.10. XPS Analysis of RFPU

The regenerated PU hard foams prepared by different degradation systems were tested by XPS, as shown in Figure 14. Comparing the a and b curves in Figure 14 and detail data in Table 2 shows that the C, N, and O elements in the polyurethane are decreased when the Fluoroalcohol is modified, indicating that Fluoroalcohol has an inhibitory effect on the polyurethane foaming process. This is because, in the foaming process, Fluoroalcohol has only one hydroxyl group, and the polyurethane produced in the foaming process has a long chain blocked by Fluoroalcohol, so the polyurethane foaming process blocked by the final preparation of fluorine-containing recycled polyurethane groups is also diminished [21,48,49,50,51,52]. By comparing b and c curves, it can be seen that the F content of the RFPU prepared by Fluorodiols is significantly higher than that of Fluoroalcohol. This is because Fluorodiols with two hydroxyl groups can be better combined with polyurethane segments to obtain longer polyurethane long chains; by comparing the a and c curves, it can be seen that the N element increases significantly, which indicates that the Fluorodiol contributes to the synthesis of hard polyurethane segments, which improves the thermal stability and mechanical properties of RFPU [53,54,55].
Since fluorine-containing polyurethane has a low surface energy during the foaming process, the hard segment is pulled to the foam surface to form a film, and this increase in the length of the Fluoroalcohol side chain facilitates the migration of the fluorinated side chain. In addition, since the fluorine side chain is attached to the hard segment of the polyurethane molecular chain, the influence of the hard segment is affected.

4. Conclusions

Waste PU was successfully alcoholized into oligomer polyols using self-made Fluorodiol and EG, DEG, and a two-component alcoholizing agent. RFPU rigid foam composites with excellent properties can be prepared using fluorinated recycled polyols as raw materials. The specific performance of the material is as follows.
The addition of fluorine-containing groups can greatly improve the performance of RFPU. When the addition of Fluorodiol was 8% of the mass of waste polyurethane, the compressive strength was 0.315 MPa, which was 43.2% higher than that of RFPU prepared by the RRPU. The waterproof performance of the RFPU was significantly improved, and the immersion loss rate was 2.125%, which was 75.59% lower than that of the RFPU prepared by RRPU. The thermal conductivity reaches 0.0227 W/m·K, which is 20.3% lower than the commercially available sample, indicating its excellent thermal insulation performance. The pore walls of the prepared RFPU are thick and uniform, and the skeleton geometry is also positive.
The raw materials used in the RFPU are waste polyurethane degradation products, and the properties of the prepared samples are comparable to or even better than commercially available PU materials. Thus, preparing the RFPU successfully demonstrated a high-value utilization of waste polyurethane. This will make polyurethane material a green and sustainable environmental protection material. This material also offers a new choice to help protect the Earth’s resources.

Author Contributions

Conceptualization, X.-H.G. and D.-S.Z.; methodology, X.-H.G. and D.-S.Z.; software, D.-S.Z.; validation, D.-S.Z., X.-H.G. and Q.-Y.Z.; formal analysis, D.-S.Z.; investigation, S.-W.L. and Q.-Y.Z.; resources, S.-W.L. and Y.-W.Z.; data curation, D.-S.Z.; writing—original draft preparation, D.-S.Z.; writing—review and editing, D.-S.Z. and X.-H.G.; visualization, D.-S.Z.; supervision, X.-H.G. and S.-W.Z.; project administration, X.-H.G., Y.L. and S.-W.Z.; funding acquisition, X.-H.G. and Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Heilongjiang Provincial Department of Education Project, grant number CLKFKT2021Z3, 145109301.

Institutional Review Board Statement

Not applicable for studies not involving humans.

Informed Consent Statement

Not applicable for studies not involving humans or animals.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Synthesis schematic diagram of Fluorodiol (RF are several CF groups on fluoroalcohol).
Figure 1. Synthesis schematic diagram of Fluorodiol (RF are several CF groups on fluoroalcohol).
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Figure 2. Schematic formula of fluorinated polyether polyol (R1 is other groups on the long chain of polyurethane; RF are several CF groups on fluoroalcohol).
Figure 2. Schematic formula of fluorinated polyether polyol (R1 is other groups on the long chain of polyurethane; RF are several CF groups on fluoroalcohol).
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Figure 3. Main schematic formula of fluorinated recycled polyurethane (R1 is other groups on the long chain of polyurethane; RF are several CF groups on fluoroalcohol).
Figure 3. Main schematic formula of fluorinated recycled polyurethane (R1 is other groups on the long chain of polyurethane; RF are several CF groups on fluoroalcohol).
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Figure 4. Infrared absorption spectra of Fluoroalcohol and Fluorodiol.
Figure 4. Infrared absorption spectra of Fluoroalcohol and Fluorodiol.
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Figure 5. FTIR spectra of regenerated polyols (a: polyether polyol 4110; b: regenerated polyether polyol; c: comparison of fluorinated recycled polyether polyols; d: fluorinated regenerated polyether polyol).
Figure 5. FTIR spectra of regenerated polyols (a: polyether polyol 4110; b: regenerated polyether polyol; c: comparison of fluorinated recycled polyether polyols; d: fluorinated regenerated polyether polyol).
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Figure 6. Effect of the addition of different amounts of Fluorodiol on viscosity and hydroxyl value of regenerated fluoropolyether polyols.
Figure 6. Effect of the addition of different amounts of Fluorodiol on viscosity and hydroxyl value of regenerated fluoropolyether polyols.
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Figure 7. Density curves of RFPU prepared with different Fluorodiol ratios.
Figure 7. Density curves of RFPU prepared with different Fluorodiol ratios.
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Figure 8. Water-absorption curves of RFPU prepared with different amounts of Fluorodiol.
Figure 8. Water-absorption curves of RFPU prepared with different amounts of Fluorodiol.
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Figure 9. Water immersion loss rate curve of RFPU prepared with different Fluorodiol ratios.
Figure 9. Water immersion loss rate curve of RFPU prepared with different Fluorodiol ratios.
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Figure 10. Effect of different fluoroalcohols on compressive strength of RFPU rigid foam (a: RRPU; b: fluoroalcohol comparison samples; c: RFPU (6%); d: RFPU (8%); e: RFPU (10%)).
Figure 10. Effect of different fluoroalcohols on compressive strength of RFPU rigid foam (a: RRPU; b: fluoroalcohol comparison samples; c: RFPU (6%); d: RFPU (8%); e: RFPU (10%)).
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Figure 11. Thermal conductivity of polyurethane with different components: (a) pure 4100 sample; (b) RRPU; (c) fluoroalcohol comparison samples; (d) RFPU (6%); (e) RFPU (8%) and (f) RFPU (10%).
Figure 11. Thermal conductivity of polyurethane with different components: (a) pure 4100 sample; (b) RRPU; (c) fluoroalcohol comparison samples; (d) RFPU (6%); (e) RFPU (8%) and (f) RFPU (10%).
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Figure 12. Scanning electron microscopy of RFPU.
Figure 12. Scanning electron microscopy of RFPU.
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Figure 13. TG curves of RFPU with different amounts of Fluorodiol.
Figure 13. TG curves of RFPU with different amounts of Fluorodiol.
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Figure 14. XPS full spectrum of regenerated PU rigid foam prepared by different degradation systems (a: RRPU; b: fluoroalcohol comparison samples; c: RFPU (8% Fluorodiol addition)).
Figure 14. XPS full spectrum of regenerated PU rigid foam prepared by different degradation systems (a: RRPU; b: fluoroalcohol comparison samples; c: RFPU (8% Fluorodiol addition)).
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Table
Table 1. Molecular weight distribution of regenerated polyols degraded by different mass concentration gradients of Fluorodiol.
Table 1. Molecular weight distribution of regenerated polyols degraded by different mass concentration gradients of Fluorodiol.
Fluorodiol Addition %MnPDI
Polyether 411011041.179
024651.217
226821.242
427341.234
627441.254
828121.255
1134551.322
Table
Table 2. Element composition of different polyurethanes.
Table 2. Element composition of different polyurethanes.
CFNO
a67.990.397.7821.05
b65.308.365.2318.25
c58.9321.095.3514.63
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Zhang, D.-S.; Gu, X.-H.; Liu, S.-W.; Liu, Y.; Zhou, Q.-Y.; Zhu, S.-W.; Zhu, Y.-W. Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane. Sustainability 2022, 14, 15685. https://doi.org/10.3390/su142315685

AMA Style

Zhang D-S, Gu X-H, Liu S-W, Liu Y, Zhou Q-Y, Zhu S-W, Zhu Y-W. Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane. Sustainability. 2022; 14(23):15685. https://doi.org/10.3390/su142315685

Chicago/Turabian Style

Zhang, Da-Sheng, Xiao-Hua Gu, Si-Wen Liu, Yan Liu, Qing-Yun Zhou, Shang-Wen Zhu, and Yan-Wei Zhu. 2022. "Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane" Sustainability 14, no. 23: 15685. https://doi.org/10.3390/su142315685

APA Style

Zhang, D. -S., Gu, X. -H., Liu, S. -W., Liu, Y., Zhou, Q. -Y., Zhu, S. -W., & Zhu, Y. -W. (2022). Study on Properties of Regenerated Fluorinated Polyurethane Rigid Foam Prepared by Degrading Waste Polyurethane. Sustainability, 14(23), 15685. https://doi.org/10.3390/su142315685

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