3.1. Chemical Analysis of the Raw Materials
Table 1 shows the highly significant differences (
P < 0.01) between the wood and non-wood raw materials in terms of the chemical parameters of the raw materials (benzene–alcohol extractives, lignin, holocellulose, and ash content).
The results for the chemical compounds of the raw materials (
Table 2) show that benzene–alcohol extracts, lignin, holocellulose, and ash content were 1.73–13.16%, 16.66–42.33%, 53.37–63.40%, and 1.66–6.73%, respectively. The holocellulose content in
S. bicolor stalks was in accordance with the range of values reported in the literature: 71.0% [
16], 67.2% [
23], 68.0% from depithed extraction [
85], 61.6% extracted with 1% NaOH [
85], 69.0% from depithed extraction [
86], and 61.6% extracted with 1% NaOH [
86]. The average pulp yield from
S. bicolor stalks was 45%, and the average kappa number was 14–18 when 16–20% sodium (NaOH) and a 1.5 h cooking time at 160 °C were used [
12]. The holocellulose content in
Z. mays (62.33%) and
S. bicolor (63.40%) stalks was higher than that in lotus leaf stalks (53.8%) [
87].
The lignin content in wood from
B. spectabilis (35.87%),
F. altissima (41.33%), and
F. elastica (42.33%) was much higher than that in hardwood species (25–35%) [
19],
Eucalyptus globulus (23.9%),
E. nitens (25.5%),
E. urograndis (26.6%), red oak (27.7%), cottonwood (21.5%), sweet gum (27.2%), acacia (26.8%), birch (22.8%), red alder (24.4%), maple (25.9%) [
33], and the poplar cultivar ‘Hybrid 275’ (18.0%) [
20]. Additionally, it was higher than that in softwood species such as European larch (31.2%), birch (26.6%), and pine (26.4%), as well as some other non-wood materials such as tall wheatgrass (13.6%), smooth bromegrass (13.7%), tall fescue (14.0%), switchgrass (17.4%), and
Miscanthus giganteus (17.8%) [
20].
The lignin content in
S. bicolor (16.66%) and
Z. mays (18.66%) stalks was in the range of that in non-wood monocotyledon species (9–20%) [
19]. The lignin content in
S. bicolor was equal to that found in depithed and extracted samples (16.1%) [
16] and lower than that found in tropical hardwoods (25–35%) [
19]. The lignin content in both
S. bicolor and
Z. mays was lower than in bamboo (26%) [
19], rice hulls (20.44%) [
88], and lotus leaf stalks (25.4%) [
87], and higher than that in smooth bromegrass (13.7%) and tall fescue (14.0%) [
20]. The content was also partially in the range of that reported for switchgrass (17.4%),
Miscanthus giganteus (17.8%) [
20], sugar beet (17.67%) [
88], and
S. bicolor stalks (17.4%) [
23]. The ash content was high, especially in
S. bicolor, but others were within the range of tropical hardwood (1 to 3%) [
89].
Among the studied materials, it can be seen from the above results that Z. mays and S. bicolor stalks had the highest amounts of benzene–alcohol extract and holocellulose. F. altissima and F. elastica wood showed the highest lignin content, while S. bicolor stalks, followed by B. spectabilis wood, had the highest ash content.
3.2. Chemical Analysis of the Produced Pulp
All pulp properties studied (ash content, residual alkali, Kappa number, screen pulp yield, freeness (Schopper–Riegler, (°SR)) were observed to have highly significant differences (
P < 0.01) among the studied wood and non-wood raw materials (
Table 3). In terms of the pulp properties (
Table 4), the ash content, residual alkali, Kappa number, screen pulp yield, freeness (°SR), and rejects were 1.76–13.53%, 1.23–7.75 g/L, 16.66–35.66, 35.33–41.00%, 24.33–33.33 °SR, and 0.13–4.23%, respectively.
The Kappa numbers for
B. spectabilis (35.66),
F. altissima (31.33), and
Ficus elastica (35.33) pulps were higher than those of
E. globulus (17) [
34], poplar cultivar ‘Hybrid 275’ (20.63) [
20],
E. camaldulensis (24), and
M. sinclairii pulps (18) [
30]. Additionally, the Kappa numbers recorded for
Z. mays and
S. bicolor pulps were comparable with that recorded for
E. globulus pulp (17) [
34] and lower than that for bamboo (
Gigantochloa scortechinii) (14.2–18.1) [
90]. Kraft pulping of bamboo chips was observed to produce a Kappa number of 17.4 [
91], which is nearly comparable with our results for
Z. mays (16.66) and
S. bicolor (17.66). Additionally, the value was lower than those for some softwood pulps such as European larch (56.83), birch (23.38), and pine (42.22) [
20]. Furthermore, the Kappa numbers for
Z. mays and
S. bicolor were slightly higher than those for other non-wood materials such as tall wheatgrass (12.25%), smooth bromegrass (14.42), tall fescue (12.71%), switchgrass (13.71), and
Miscanthus giganteus (14.31) [
20]. Results from the Soda-AQ pulping of rice straw showed Kappa numbers ranging from 12.3 to 26 depending on the mesh size [
18].
It can be summarized that pulp produced from S. bicolor stalks, F. altissima wood, B. spectabilis/F. elastica wood, B. spectabilis wood, and Z. mays stalks showed the highest ash%, residual alkali g/L, screen pulp yield, freeness (°SR), and rejects (%) values, respectively.
3.3. Mechanical and Optical Properties of the Produced Handsheets
Table 5 shows that all the mechanical and optical properties (tensile index N·m/g, tear index mN·m
2/g, burst index kPa·m
2/g, double fold number, opacity %, and brightness %) among the studied handsheets from wood and non-wood raw materials were statistically highly significant effects (
P < 0.01).
Table 6 shows that the highest tensile index was observed with handsheets produced from
Z. mays (47.43 N·m/g), followed by those produced from
S. bicolor (44.33 N·m/g) and
F. elastica (40 N·m/g). The highest tear index was found in handsheets produced from
Z. mays (5.87 mN·m
2/g), followed those produced from
S. bicolor (4.75 mN·m
2/g). Additionally, handsheets produced from pulps of
Z. mays and
S. bicolor showed the highest burst index and double fold number with values of 4.76 kPa·m
2/g and 55 and 3.92 kPa·m
2/g and 36.33, respectively. The highest opacity percentages were observed for handsheets produced from
F. elastica wood (99.8%) and
F. altissima wood (99.1%), while the lowest value was found with handsheets produced from
Z. mays stalks (93.56%). Handsheets produced from
Z. mays and
S. bicolor stalks were observed to have the highest brightness values: 35.33% and 32.66%, respectively. The burst index (3.92 kPa·m
2/g) of the
S. bicolor handsheet was higher than that reported for
S. bicolor x S. bicolor var. sudanense pulp grown in Turkey under optimum conditions (3.56 kPa·m
2/g) [
16]. The burst index ranged from 0.16 to 0.29 kPa·m
2/g in sweet sorghum bagasse [
23] and was equal as reported to the values reported in papers that produced pulp from
Populus tremula via the kraft method (3.85 kPa·m
2/g) [
32]. The unrefined unbleached pulp from
Z. mays stalks had a tensile index, burst index, tear index, and double fold number of 49.1 N·m/g, 3.80 kN/g, 7.53 mN·m
2/g, and 86, respectively [
22]. In another study, a tensile index of 9.1 N·m/g and a tear index (1.2 N·m/g) were reported for pulp produced from corn stalks [
15]. The tensile index of corn stalk pulp ranged from 52 (unbeaten state) to 77.0 N·m/g (beaten state) [
24] and from 1.83 to 4.39 N·m/g [
23]. For our raw materials, the tear index values were similar to those of other materials such as the oil palm leaf (1.8 N·m
2/g), date palm rachis (4.4 N·m
2/g), and palmyra fruit (1.1 N·m
2/g), while our results for the tensile index were higher than that obtained for the oil palm leaf (7.9 N·m/g) and similar to those obtained for the date palm rachis (1.09 N·m/g) and palmyra fruit (13.8 N·m/g) [
15].
The burst index value measured for handsheets from
Z. mays pulp (4.76 kPa·m
2/g) was lower than that for corn stalk (6.6 kPa·m
2/g) but higher than that for date palm rachis (1.32 kPa·m
2/g) and oil palm leaf (0.9 kPa·m
2/g) [
25]. In the folding test, handsheets from corn stalks produced a value of 55 N, while another study reported a value of 2.5 Nm and compared this with oil palm leaf (1.23 Nm) and oil palm (1.9 Nm) [
25].
The paper sheets obtained from olive tree pruning pulp were produced with different degrees of refining and were characterized by their stretch index, burst index, and tear index. All paper sheets reached a stretch index value of between 33 and 39 kNm/kg, a burst index of between 1.5 and 2 kN/g, and a tear index of 0.7–2.5 N·m
2/g. A high refining degree was not used (<45 °SR) [
92,
93]. Pulp from empty fruit bunches from oil palm showed a burst index value of 4.17 kN/g and a tear index of 7.20 mN·m
2/g, for a degree of refining of 47.5 °SR, acceptable for the formation of handsheets [
2]. Pulp paper made from sunflower seeds had a burst index of 1.15 kN/g and a tear index of 2.04 mN·m
2/g [
13]. Paulownia wood pulp was used to produce paper sheets with a brightness of 27.4% ISO, a tensile index of 28.87 N·m/g, a burst index of 1.22 kPa.m
2/g, and a tear index of 1.23 kN·m
2/g [
94].
H. funifera pulp showed a tensile index of 83.6 N·m/g, a burst index of 7.34 kN/g, and a tear index of 3.20 mN·m
2/g [
14]. The tensile index of degummed whole cotton stalk pulp ranged from 23.40 to 40.54 N·m/g, and the tear index ranged from 3.95 mN·m
2/g to 4.52 mN·m
2/g [
17]. The mechanical properties of handsheets produced from
Z. mays and
S. bicolor stalk pulps were comparable to those from rice straw: a burst index of 2.43–5.34 kPa·m
2/g, folding endurance of 35–173, a tear index of 6.49–7.49 mN·m
2/g, and a tensile index of 38.0–55.2 N·m/g, depending on the mesh size [
18]. Another study measured the tensile index (N·m/g), burst index (kPa·m
2/g), and tear index (mN·m
2/g) of pulp from the European larch (90.0, 7.8, 8.0), birch (105.8, 7.2, 3.8), pine (103.9, 6.9, 6.1), poplar cultivar ‘Hybrid 275’ (109.0, 8.3, 3.8%), tall wheatgrass (81.6, 6.4, 3.2%), smooth bromegrass (89.0, 7.1, 4.4), tall fescue (85.7, 6.2, 4.4%), switchgrass (68.9, 4.3, 3.7), and
Miscanthus giganteus (73.4, 4.4, 3.7), respectively [
20].
Handsheets from
Z. mays and
S. bicolor stalks had the highest values for mechanical properties. Additionally, the folding endurance strength showed that paper from those materials could achieve higher folding numbers than those from the hardwood species investigated in this study. Other studies revealed that
Ficus species with large amounts of parenchyma have a significantly lower ratio of fibers to non-fibrous tissue [
26], leading to a lower yield of pulp and a problem of binding resulting from the ‘fine fibers’ [
95].
3.4. Antifungal Activity and SEM Examination of MAHE-Treated Handsheets
Figure 2 presents the antifungal activity of the produced handsheets that were previously treated with MAHE against three mold fungi (
Aspergillus fumigatus,
Fusarium culmorum and
Stemphylium solani). The fungal inhibition zones (in mm) and the fungal growth on the treated discs are presented in
Table 7.
Fourteen days after incubation, and with an increase in the extract concentration, the inhibition or suppression of fungal growth occurred. According to visual observations and compared with the control treatments, no fungal growth of
A. fumigatus occurred on paper discs of
B. speclabilis pulp wood or pulp paper produced from
Z. mays and
S. bicolor stalks and treated with 1% MAHE, or pulp paper produced from
F. elastica and treated with 0.50% and 1% of MAHE. At MAHE concentrations of 0.50% and 1%,
F. culmorum showed no growth on paper discs manufactured from
B. speclabilis,
F. altissima,
F. elastica, and
Z. mays pulp, with visual inhibition zones found (
Table 7), while no growth was found following treatment with 1% MAHE on paper discs made from
S. bicolor pulp. Furthermore, nearly no growth of
S. solani was found on paper discs manufactured from the raw materials treated with 1% MAHE, and inhibition zones were found.
SEM examinations of (
Figure 3,
Figure 4,
Figure 5,
Figure 6,
Figure 7,
Figure 8,
Figure 9,
Figure 10,
Figure 11 and
Figure 12) the paper discs made from the studied materials, treated with MAHE, and inoculated with the three mold fungi were conducted to observe and show how this MAHE acts against the growth of the studied fungi by suppressing their hyphal and mycelial growth.
Figure 3 shows huge, dense fungal mycelia growth (FMG) of
F. culmorum on the paper discs made from untreated samples (control, 10% DMSO). Additionally, with the application of 0.25% MAHE, dense FMG was still found for
F. culmorum (
Figure 4). With 0.5% MAHE, the FMG of
F. culmorum was suppressed and the hyphal mass growth was reduced, as shown in
Figure 5a,b. Examination of
F. elastica pulp wood treated with 1% MAHE under SEM found no FMG of
F. culmorum and fibers were clearly shown (
Figure 5c).
Figure 6 shows the dense FMG of
A. fumigatus on paper discs treated with 10% DMSO (control) made from
B. speclabilis (
Figure 6a),
Ficus altissima (
Figure 6b),
F. elastica (
Figure 6c),
Z. mays (
Figure 6d), and
S. bicolor pulp (
Figure 6e). The FMG of
A. fumigatus began to decrease following treatment of the paper discs with 0.25% MAHE, as shown in
Figure 7. Following treatment with 0.5% MAHE, paper discs made from pulps of
B. speclabilis (
Figure 8a),
F. altissima (
Figure 8b), and
F. elastica (
Figure 8c) showed low FMG of
A. fumigatus, as the extract suppressed the FMG of
A. fumigatus, and the fibers were more clearly shown. In the SEM examination, FMG of
S. solani was clearly shown, with dense growth over the fibers of untreated (control 10% DMSO) handsheets made from
B. speclabilis (
Figure 9a),
F. altissima (
Figure 9b), and
F. elastica pulp (
Figure 9c).
FMG was reduced in the treated handsheets treated with 0.25%
Z. album extract, but growth was still dense, as
S. solani mycelia were found over and between the fibers (
Figure 10). Low or even no FMG of
S. solani was found when the handsheets were treated with 0.5% MAHE, and weak interconnections of hyphae with the fiber structure of the paper were found (
Figure 11). The FMG of
S. solani was nearly suppressed (
Figure 12a,c) or completely suppressed (
Figure 12b) following the application of 1% MAHE to the produced handsheets.
These results are in agreement with those of previous studies [
96]. Papyrus strips pretreated with natural extracts were enhanced in terms of the technological (mechanical and optical) and antifungal (against
A. flavus,
A. niger, and
C. gloeosporioides) properties of the produced papyrus sheets [
8]. In a previous study, the novel combination of chitosan or Paraloid B-72 c with nanoparticles of Ag, ZnO, or cellulose was used to produce antifungal handsheets. The huge growth of
A. flavus,
A. terreus, and
S. solani that was observed on handsheets produced with pulp with additives of chitosan and Paraloid B-72 at 4% was compared with pulp without additives [
9]. The addition of powdered plant materials in the three concentrations was less or not effective at preventing the growth of the three tested fungi—
A. terreus,
F. culmorum, and
A. niger—but treated pulp from
P. rigida wood had some defense against
A. terreus and
A. niger at all tested concentrations [
7].
3.5. Testing of Phytochemical Compounds of MAHE by HPLC
The previous results clearly show that by increasing the concentration of MAHE, the suppression of fungal growth occurs. Additionally, some treatments resulted in no fungal growth. These results could be related to the phytochemical compounds present in the extract.
Table 8 presents the chemical compounds presented in MAHE. The main compounds (in mg/kg) are
p-hydroxybenzoic acid (3966.88), caffeine (1032.67), rutin (quercetin 3-
O-rutinoside) (834.13), chlorogenic acid (767.81), benzoic acid (660.64), quinol (594.86), quercetin (460.36), vanillic acid (366.13), myricetin (302.404), and caffeic acid (130.97).
Figure 13 shows the chromatogram peaks that were used to separate the chemical compounds in MAHE.
From different parts of
M. azedarach (Meliaceae family), phenolic compounds
p-coumaric acid, vanillic acid, gallic acid, caffeic acid, ferulic acid, protocatechin,
p-hydroxybenzoic acid, chlorogenic acid, rutin, and salicylic acid were identified. The ingredient components active against
Meloidogyne incognita were identified as
p-coumaric acid and
p-hydroxybenzoic acid [
97]. At a wavelength of 280 nm, the main phenolic compounds in the leaves of
Melia azedarach were found to be rutin, quercetin-3-
O-neohesperidoside, kaempferol-3-
O-rutinoside, feruloylglucaric acid, and feruloylquinic acid derivative [
98]. Extracts from different parts of
M. azedarach exhibited fungistatic activity against
A. flavus,
Diaporthe phaseolorum var.
meridionales,
F. oxysporum,
F. solani,
F. verticillioides, and
Sclerotinia sclerotiorum, where vanillin, 4-hydroxy-3-methoxycinnamaldehyde and (±)-pinoresinol were found to be the main compounds [
99]. Additionally, rutin, kaempferol 3-
O-robinobioside, and kaempferol 3-
O-rutinoside were isolated from water extract of
M. azedarach leaves [
100]. Gallic acid and (–) epicatechin were isolated from bark extract [
101]. Flavonoids naringenin, quercetin, myricetin, and dihydromyricetin were isolated from
Soymida febrifuga wood extract (Meliaceae family) [
102].