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Natural compounds from Punica granatum peel as multiple stabilizers for polyethylene.

1 | INTRODUCTION

Polyolefin, such as, polyethylene (PE) and polypropylene (PP), were widely used in packaging and pipe industry, due to their corrosion resistance, low price, and good processability. However, PE was so sensitive to light, oxygen and mechanical shear force that it was prone to photodegradation, oxidative degradation, and processed degradation. [1,2] Those degradation process could cause fading of PE, grafting and crosslinking of the molecular chains, and thereby affect its performance. [2,3] In order to solve this problem, an additive package, a composition of hindered phenol primary antioxidant and phosphorus or sulfur secondary antioxidants, was added to PE. [4] However, the study of Brocca and co-workers indicated that synthetic hindered phenol antioxidant may pose a threat to the environment and human health. [5] Consequently, more and more researches turned to the natural antioxidants.

In recent years, in order to improve the thermo-oxidative, photo-oxidative, and processing stability, various natural substances have been added to polyolefin. Quercetin and curcumin were added to PE to improve its thermooxidative and processing stability. [6-11] Dihydromyricetin and [beta]-carotene were used as thermo-oxidative stabilizers of PE and PP. [12-14] Phytic acid, cross-linked tannin and flavonoids (quercetin, chrysin, silibinin, naringin, and hesperidin) as additives of PP and PE could reduce the impact of photooxidative degradation. [15-17] These natural compounds were beneficial to the stability of polyolefin, but the purification of them requires a great deal of effort. As a result, many researchers focused on the bio-based additives, especially bio-waste, to avoid the competition with food industry. Tomato waste, [18,19] grape seeds, [18,20] pine bark tannin, [21] cork, [22] chestnut burs, [23] flax fibers, [24] and green tea [25] were reported to be beneficial to the thermo-oxidative improvement of PP and PE. Grape marc and nutshell showed great potential as UV-light stabilizer for PP and PE, respectively. [26,27] Effectiveness of agro-waste (grape pomace, turmeric waste, orange peel waste, and coffee grounds) in protecting PE from processing degradation was also reported. [28] However, up to now, there was no report on the bio-waste, which could simultaneously improve more than one stability of polyolefin. In response to this situation, our research on multifunctional stabilizer for PE begun.

Punica granatum extractive, a commercial good, sold by pharmaceutical companies for antioxidative usage. Punica granatum peel extractive (PPE) was rich in punicalagin, ellagic acid derivatives, flavanols, ellagitannins, and anthocyanins. [29,31] Moreover, PPE contained flavonol and ellagitannin, which have antibacterial activity, antioxidant activity [32,35] and the ability in scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH). [34,35] As a kind of bio-waste, the usage of PPE as stabilizer guaranteed the safety of polyolefin' additives and recycle of wastes, which was conducive to environmental protection. Thus, the application of PPE in PE modification was investigated systematically in this study. Excitedly, PPE could act as multiple stabilizer, exhibiting attractive performance in improving the UV, thermo-oxidative, processing, and mechanical stability of PE matrix.

2 | EXPERIMENTAL

2.1 | Materials

Linear low density polyethylene (LLDPE, MFR = 4 g/10 minutes, Maoming Petro-Chemical Co., Ltd), Irganox 1010 (Shanghai Aladdin Bio-Chem Technology Co., Ltd.), tetrakis (2,4-di-tert-butylphenol)[l,l-biphenyl]4,4'-diylbisphosphite (PEPQ, Shanghai Aladdin Bio-Chem Technology Co., Ltd.), and calcium stearate (CaSt, Shanghai Aladdin Bio-Chem Technology Co., Ltd.) were used as received. Punica granatum was purchased from the market. The extraction process of PPE was as follows: the Punica granatum peel was dried and ground into powder and extracted with ethanol (the weight ratio of ethanol to pomegranate peel powder was 1:10) for 3 times (2 hours extraction at 70[degrees]C). The extractive solution was directly added to PE without distillation of ethanol.

2.2 | Sample preparation

PPE, PEPQ, and ethanol were mixed with PE, then ethanol was distilled out. Prior to the extrusion, mixed PE was dried and CaSt was added. The mixture was extruded by a twin-screw extruder (screw temperature profile from hopper to die was 155[degrees]C, 180[degrees]C, 190[degrees]C, 200[degrees]C, 200[degrees]C, 195[degrees]C, 195[degrees]C, 195[degrees]C, 190[degrees]C, and 175[degrees]C) with the screw speed of 30 rpm. Then the extruded samples were pelletized and further subjected to four multi-pass extrusions under the same conditions. Samples were taken after each extrusion step. Samples added with antioxidants were abbreviated as PE-Am-P, where A referred to primary antioxidants (Irganox 1010 or PPE), m referred to the added content, and P referred to PEPQ. The specific formulations and abbreviations were listed in Table 1.

2.3 | Characterization

The PPE was analyzed by Fourier transform infrared spectroscopy (FTIR, Nicolet iS50) and mass spectra (MS, ACQUITY UPLC M-Class/Synapt G2-Si HDMS). The FTIR test performed 32 scans at a resolution of 4 [cm.sup.-1]. The MS was tested with chloroform as the solvent.

Oxidation onset temperature (OOT) was measured by differential scanning calorimetry (DSC, HS-DSC-101, China) according to M. D. Samper's method. [17] Samples were heated under air (50 ml/min) from 40[degrees] C to 300[degrees]C at a rate of 5[degrees]C/min. The OOT was evaluated as the temperature at which the exothermic slop was the highest after melting peak. The value of OOT was the average of three tests.

UV-light accelerated aging of samples was carried out in UV accelerated weathering tester (BG5118, China). The samples were exposed to continuous irradiation with an irradiation intensity of 0.68 W/(m2nm) for 168 hours at 60[degrees]C. The thermo-oxidative accelerated aging of samples was performed in oven with air circulation (70 times/min) for 28 days at 80[degrees] C. The samples before and after UVlight/thermo-oxidative aging was characterized by Attenuated Total Reflection Fourier transform infrared spectroscopy (ATR-FTIR, Nicolet iS50) under a resolution of 4 [cm.sup.-1] for 32 scans. Carbonyl index (CI) was applied to characterize the degree of degradation. The CI was calculated according to following equation:

CT(%) = [A.sub.c]/[A.sub.r] * 100% (1)

where [A.sub.c] refers to the area of the carbonyl band at 1550 to 1780 [cm.sup.-1], [A.sub.r] refers to the area of asymmetric vibration of C--H band (methylene groups) at 2850 to 2920 [cm.sup.-1]. Since pomegranate peel extract contains carbonyl groups (Figure 1), the carbonyl area of [A.sub.c] of samples PE-[PPE.sub.0.7%]-P and PE-[PPE.sub.2%] was subtracted from the area of before UV aging for the purpose of precise calculation.

Melt flow rate (MFR) of samples were tested by an MFR apparatus (XNR-400 AM, China) at 190[degrees]C with a 5 kg load according to ASTM D 1238 standard. The value of MFR was the average of three tests.

Tensile tests of dumbbell shaped samples (dimensions: total length: 150 mm, width: 10 mm, thickness: 4 mm) were prepared by injection molding machine according to GB/T 1040.1-2018 standard, and then performed by tensile machine (AI-7000 M, China) with a 20 kN load cell at a clamp separation rate of 50 mm/min. Each sample was tested five times.

3 | RESULTS AND DISCUSSION

3.1 | Main structure analysis of PPE

Figure 1 shows the FTIR spectrum of PPE. The peaks at 1731, 1444, and 1343 [cm.sup.-1] were derived from the vibration of C=0, the deformation vibration of C--H and the plane bending of O--H, respectively. [26,27] The band at 1048 to 1219 [cm.sup.-1] included the stretching vibration of C--OH side groups of polysaccharide and C--O--C of glycosidic linkage.36 The presence of phenolic hydroxyl group was evidenced by the broad band at 3280 [cm.sup.-1]. The peaks at 2926 and 1614 cnT1 were attributed to the =C--H ([sp.sup.2]) vibration and C=C vibration on the aromatic ring. [27,37] The peak at 1348 [cm.sup.-1] was related to the stretching or deformation vibration of C--O--H (phenolic compound). [36] The existence of these bands indicated the existence of phenolic compounds in PPE. In addition, the test of MS suggested that PPE contained phenolic compounds, such as, punicalagin, punicalin, ellagic acid, and other phenolic compounds (Figure 2 and Table S1), which was consist with previous research. [29,38,39]

3.2 | Thermo-oxidative stability

The effect of antioxidants on the thermo-oxidative stability of PE was evaluated by both short-term and long-term aging, which were characterized by OOT and carbonyl index (CI), respectively.

Figure 3 showed the OOT values of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%] -P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples. Clearly, the OOT value of PE was the lowest and the OOT value of all modified samples obtained after fifth extrusion were even higher than the one of PE after first extrusion. It indicated that PE underwent severe degradation during the extrusion process. Comparing the results of natural antioxidant and the commercial one, it could be noticed that although the OOT values of sample PE-[PPE.sub.0.12%]-P (222[degrees]C) were not as good as PE-[1010.sub.0.12%]-P (241[degrees]C), it was still higher than pure PE (210[degrees] C). It means that PPE was a good protector against thermo-oxidative degradation.

Samples with increased PPE content and without addition of PEPQ were prepared to further confirm the effect of PPE in protecting PE. The OOT value of PE-[PPE.sub.0.7%]-P and PE-[PPE.sub.2%] samples could also be found in Figure 3. The addition of PPE and PEPQ resulted in ca. 14[degrees]C increase of OOT value. More excitedly, a 22[degrees]C increase of OOT value could be achieved with the addition of 2 wt% PPE, suggesting the favorable performance of PPE in stabilizing PE. This result was very important in the greenization of PE additives.

The carbonyl index (CI) could also characterize the thermo-oxidative of PE. [40] The CI of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after first extrusion) before and after long-term aging were presented in Figure 4. Due to the formation of carbonyl products (carboxylic acids, esters, and ketones), the degradation of PE would increase the CI. [40] After thermo-oxidative aging, the CI value of PE was the highest in all investigated samples, suggesting its fastest degradation during the process. It also indicated that the addition of antioxidants inhibited the degradation of PE matrix. Comparing the results of natural antioxidant (PEPPEo.12% -P) and the commercial one (PE-[1010.sub.0.12%]-P), it could be concluded that the contributions of PPE was similar to that of Irganox 1010 in postponing thermooxidative degradation of PE matrix. Besides, it should be noticed that the CI of PE-[PPE.sub.2%] sample was almost the same as PE-[1010.sub.0.12%]-P, and PE-[PPE.sub.0.12%]-P. It meant that excellent thermo-oxidative stability of PE could be achieved in the absence of PEPQ and it meant a lot in the development of polyolefin.

Both short-term and long-term results indicated that PPE was an effective protector of PE against thermooxidative degradation and it could be used alone as efficient additive.

3.3 | UV-light stability

It was known that PE was sensitive to sunlight or UV light in the presence of air. The oxidation of PE leaded to the formation of hydroperoxide, which was absorbed in UV region and subsequently reacted to form carbonyl products. [2,27] In order to evaluate the potential of PPE as UV stabilizer of PE, all sample were exposed to continuous UV irradiation for 168 hours at 60[degrees]C. Because the carbonyl products were also formed after photo-oxidation of PE, [41] so the structural changes of PE and modified PE before and after UV light irradiation were characterized by ATR-FTIR. Figure 5 showed the FTIR spectra of PE, PE-[1010.sub.0.12%]-P) PE"[PPE.sub.0.12%]-P) PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after first extrusion) before and after UV-light irradiation. The CI values of all samples were displayed in Figure 6.

Prior to UV irradiation, there was no significant absorption at 1550 to 1780 [cm.sup.-1] for PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, and PE-[PPE.sub.0.7%]-P samples, but a clear absorption at 1550 to 1780 [cm.sup.-1] could be observed for PE [PPE.sub.2%] sample (originated from PPE, Figure 1). After irradiation, the band at 1550 to 1780 [cm.sup.-1] was more pronounced for PE and PE-[1010.sub.0.12%]-P, and the CI values were 36% and 30%, respectively. It could be due to the formation of carbonyl oxidation products, such as, aldehyde, ketone, ester and carboxylic acid,2'24 and indicated the rapid degradation of PE and PE-[1010.sub.0.12%]-P samples by UV irradiation. As for the three samples modified with PPE, only slight increase of intensity could be observed and their CI values were all below 20%, indicating that PPE was better protector than Irganox 1010 against UV irradiation. In addition, comparing the data of PE[PPE.sub.0.12%]-P, PE-PPE0i7%-P, and PE-[PPE.sub.2%] samples, it could be concluded that PPE alone was also effective in stabilizing PE against UV degradation.

Furthermore, there was an interesting phenomenon: the carbonyl products, such as, lactones (1780 [cm.sup.-1], Figure S1), esters (1741 [cm.sup.-1]), carboxylic acids (1701 [cm.sup.-1]), and unsaturated ketones (1605 [cm.sup.-1]) formed by photooxidation of different samples (PE, PE-[1010.sub.0.12%]-P and PE-[PPE.sub.2%]) were different, indicating that the addition of different kinds of antioxidants (Irganox 1010 and PPE) will cause different carbonyl products 40 It may be due to the reaction between antioxidants and PE during UV irradiation.

3.4 | Processing stability

MFR was a sign of processing stability of polyolefin. For PE, chain-scission may compete with crosslinking, but crosslinking predominated for PE. [3] So, the viscosity of PE increases would result in the decrease of MFR value. [2,3] Therefore, constant value of MFR meant high processing stability of PE.

Figure 7 depicted the MFR values obtained after each extrusion. For PE sample, the MFR value decreased rapidly with the increase of extrusions, indicating that PE degraded dramatically by mechanical shearing force during processing. For the four modified samples, the MFR values were much more stable. Figure 8 showed the change of MFR value between first and fifth extrusion ([DELTA][MFR.sub.5-1]). Obviously, PE possessed the highest [DELTA][MFR.sub.5-1] (2.2 g/10 minutes). Comparing PE-[1010.sub.0.12%]-P and PE-[PPE.sub.0.12%]-P, PPE could protect the PE matrix more effectively than Irganox 1010 under mechanical shear condition. The [DELTA][MFR.sub.5-1] values of PE-PPE07%-P and PE-[PPE.sub.2%] were almost the same, ca. 10% of [DELTA][MFR.sub.5-1] of PE. It revealed that PPE and PEPQ were effective in stabilizing PE against mechanical shear force. Moreover, PPE could be used alone as the processing stabilizer for PE.

3.5 | Mechanical properties

Mechanical properties were important features, which should be considered in the application of polymers. The degradation of polyolefin could cause the breakage, branching, and cross-linking of molecular chains, leading to the decrease of mechanical properties (eg, reduction of tensile strength and elongation at break). [28] Mechanical properties of samples were evaluated by stress-strain curves (Figure S2). The addition of 0.12 wt% Irganox 1010 or PPE increased the Young's modules of PE (Figure 9). Increasing the amount of PPE, the sample's (PE[PPE.sub.0.7%]-P and PE-[PPE.sub.2%]) Young's modules was also equivalent to PE. This showed that addition of PPE could maintain or improve the Young's modules of PE.

Figures 10 and 11 showed the tensile strength and elongation at break of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples obtained after first and fifth extrusions, respectively. Clearly, the tensile strength of PE decreased greatly after five extrusions (16 MPa for first extrusion and 13 MPa for fifth extrusion) and the elongation at break also decreased (450% for first extrusion and 295% for fifth extrusion). It demonstrated the degradation of PE during processing which was consist with the decrease of MFR values (Section 3.4). However, only slight change of tensile strength and elongation at break were detected for four modified samples. Comparing the results of natural antioxidant (PE-[PPE.sub.0.12%]-P) and the commercial one (PE[1010.sub.0.12]*-P), it should be noticed that Irganox 1010 and PPE contributed similarly to the improvement of mechanical properties of PE matrix. In addition, the tensile strength and elongation at break of PE-[PPE.sub.2%] sample maintained within five extrusions, revealing that PPE could be used alone for the maintenance of mechanical properties of PE during processing.

In order to further confirm the effect of PPE, the mechanical properties of samples after UV irradiation were investigated (Figure S3A). After UV irradiation, Young's modules of PE and four modified samples were comparable (Figure S3B). This proved that addition of Irganox 1010 or PPE had no effect on the Young's modules of PE under UV environment.

Figure 12 showed the tensile strength and elongation at break of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after fifth extrusion) before and after UV irradiation. As expected, the mechanical properties of PE decreased, especially the elongation at break (ca. 44% loss). While the decline of mechanical properties reduced for all modified samples. Both PE-[1010.sub.0.12%]-P and PE-[PPE.sub.0.12%]-P samples exhibited the lowest loss. It suggested that the additives did a good job in protecting the PE matrix and the effect of PPE was comparable with 1010. As for PE-[PPE.sub.2%] sample, although the loss of elongation at break was the highest in all modified samples, its mechanical properties after UV irradiation were still much higher than those of PE before UV irradiation. It suggested that in UV environment, PPE alone could also play an important role in preserving the mechanical properties of PE matrix.

3.6 | Color

The color of polyolefin products is important in some applications, but it does not matter in some products (dark products).7 Due to the presence of phenolic compounds in PPE, the addition of PPE colored the PE matrix (Figure S4). According to the above discussion, PPE addition could inhibit the degradation of PE and its performance was comparable with commercial antioxidant. Thus, PPE could be used as the stabilizer of PE in the field, which do not strict restriction on the product color.

4 | CONCLUSION

In present study, pomegranate peel extractive (PPE) was applied as PE stabilizer for the first time. In order to assess the effect of PPE on PE matrix, four modified samples were prepared: PE-[PPE.sub.0.12%]-P, PE-PPE07%-P, PE[PPE.sub.2%], and PE-[1010.sub.0.12%]-P. Results showed that the effect of PPE in maintaining the thermo-oxidative stability, processing stability, and mechanical properties of PE matrix was comparable with commercial antioxidant (Irganox 1010). However, the performance of Irganox 1010 in protecting PE against UV irradiation was not as good as PPE: The CI values of PE-[PPE.sub.0.12%]-P was ca. 46.7% lower than that of PE-10100.12%-P. Moreover, the addition of PPE alone could also give good protection of PE. All results revealed that pomegranate peel extractive was a good and multiple stabilizer for PE.

ACKNOWLEDGEMENTS

This work was funded by the Research Foundation of Qingdao Fusilin Chemical Science & Technology Co., Ltd. (FSL-RF 2016, FSL-RF 2018), National Natural Science Foundation of China (Grant No. 21676285 and 21306214) and Qingdao Indigenous Innovation Program (No. 15-9-1-76-jch).

DATA AVAILABILITY

The raw/processed data required to reproduce these findings cannot be shared at this time due to legal/ethical reasons.

CONFLICT OF INTEREST

The authors declare no conflicts of interest.

ORCID

Qing Yu [ID] https://orcid.org/0000-0002-2810-486X

Received: 17 February 2020 | Revised: 28 July 2020 | Accepted: 30 July 2020

DOI: 10.1002/pen.25506

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SUPPORTING INFORMATION

Additional supporting information may be found online in the Supporting Information section at the end of this article.

Huimin Xia | Kun Sui | Tengteng Ge | Fazong Wu | Qiqi Sun | Zhongwei Wang | Liang Song | Xiaowen Huang | Qing Yu [ID]

Shandong University of Science and Technology, College of Materials Science and Engineering, Qingdao, China

Correspondence

Xiaowen Huang and Qing Yu, Shandong University of Science and Technology, College of Materials Science and Engineering, Qingdao 266590, China. Email: laura9751@163.com (Q. Yu) and Email: hxw009@sina.com (X.W. Huang)

Funding information

National Natural Science Foundation of China, Grant/Award Numbers: 21306214, 21676285; Qingdao Indigenous Innovation Program, Grant/Award Number: 15-9-1-76-jch; Research Foundation of Qingdao Fusilin Chemical Science & Technology Co., Ltd., Grant/Award Numbers: FSL-RF 2016, FSL-RF 2018

Caption: FIGURE 1 FTIR spectrum of PPE [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 2 MS spectrum of PPE [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 3 OOT values of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 4 The CI values of PE, PE-[1010.sub.0.12]%-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after first extrusion) before and after thermo-oxidative accelerated aging [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 5 FTIR spectra of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after first extrusion) before and after UV-light irradiation [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 6 The CI of PE, PE-[1010.sub.0.12]*-P, PE-[PPE.sub.0.12%]-P, PEP[PE.sub.0.7%]-P, and PE-[PPE.sub.2%] obtained after first extrusion before and after UV-light irradiation [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 7 MFR values of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] as a function of number of extrusions [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 8 The [DELTA][MFR.sub.5-1] values of PE, PE-[1010.sub.l2%]-P, PE[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 9 Young's modulus of PE, PE-[1010.sub.0.12%]-P, PE[PPE.sub.0.12%]-P> PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples obtained after first and fifth extrusion [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 10 The tensile strength of PE, PE-[1010.sub.0.12%]-P, PE[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples obtained after first and fifth extrusion [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 11 The elongation at break of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12]*-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples obtained after first and fifth extrusion [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIGURE 12 Tensile strength and elongation at break of PE, PE-[1010.sub.0.12%]-P, PE-[PPE.sub.0.12%]-P, PE-[PPE.sub.0.7%]-P, and PE-[PPE.sub.2%] samples (obtained after fifth extrusion) before and after UV irradiation [Color figure can be viewed at wileyonlinelibrary.com]
TABLE 1 The used formulations
and abbreviations in this study

Samples                    1010 (wt%)     PPE (wt%)     PEPQ (wt%)

PE                         --             --            --
PE-[1010.sub.0.12%]-P      0.12           --            0.2
PE-[PPE.sub.0.12%]-P       --             0.12          0.2
PE-[PPE.sub.0.7%]-p        --             0.7           0.2
PE-[PPE.sub.2]%            --             2             --

Samples                    CaSt (wt%)

PE                         0.5
PE-[1010.sub.0.12%]-P      0.5
PE-[PPE.sub.0.12%]-P       0.5
PE-[PPE.sub.0.7%]-p        0.5
PE-[PPE.sub.2]%            0.5
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Title Annotation:RESEARCH ARTICLE
Author:Xia, Huimin; Sui, Kun; Ge, Tengteng; Wu, Fazong; Sun, Qiqi; Wang, Zhongwei; Song, Liang; Huang, Xiao
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9CHIN
Date:Nov 1, 2020
Words:5238
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