Preparation and Characterization of Biodegradable Polylactic Acid/Polypropylene Spun-Bonded Nonwoven Fabric Slices

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L.-S. Pan1 *, Q. Yang1 ,N.Xu1 , S.-J. Pang1 , S.-F. Wang2 1 Key Laboratory of Advanced Materials of Tropical Island Resources of Ministry of Education, Institution of Materials and Chemical Engineering, Hainan University, Hainan, PRC 2 Xinlong Holding (Group) Company Ltd., Hainan, PRC Preparation and Characterization of Biodegradable Polylactic Acid/Polypropylene Spun-Bonded Nonwoven Fabric Slices

pare these fabrics include spunbonding, melt blowing, pulp air Biodegradable spun-bonded non-woven fabric slices of poly laying, needle (water) punching, chemical bonding, and ther- lactic acid (PLA)/polypropylene (PP) were prepared by melt mal bonding. PP and PE are the two most important polymer blending. The influence of the proportion of raw materials, raw materials, although the price of PE is lower than PP, the blending temperature, blending time and rotation speed on heat resistance of PP is better than PE, generally, the melt tem- the mechanical properties and melt flow properties of the perature of PP is 160*1708C, is higher than the melt tempera- slices were investigated, the influence of the proportion of ture of PE about 60*708C, at such melt temperature the pro- PLA and PP composite slices on the thermal properties and ducts can be disinfected. On the other hand, the tensile microstructure was also researched. According to the re- strength of PP is higher than PE. The spun-bonded nonwoven search results of optimization conditions, the biodegradable fabric slices in our study are expected to have high heat resis- spun-bonded non-woven fabric slice of PLA/PP was prepared tance, tensile strength and aseptic property. Therefore, nowa- and its biodegradable performance was evaluated. The results days, the main raw material of nonwoven fabric is PP, which showed that when (m)PLA:(m)PP was 8:2, blending tem- accounts for 63% of the raw materials. As PP is a linear satu- 8 perature was 185 C, blending time was 4 min and rotation rated hydrocarbon, it cannot easily undergo biodegradation in speed was 50 min–1, the melt blending condition of PLA/PP a natural environment (Yang et al., 2007), thereby leading to a composite slices was optimal. With the increase of PP mass worldwide environmental challenge. fraction in slices, slices of melt flow rate (MFR) and glass On the other hand, polylactic acid (PLA) exhibits good me- transition temperature (Tg) were on the decline; T–50%,T–95% chanical performance, biocompatibility, and heat resistance and TP were on the rise; the crystallinity of PLA/PP slices (Madhavan Nampoothiri et al., 2010), and is a new biode- \ was increased; SEM results showed that the slices had sea- gradable green product. Figure 1 shows the molecular structure " island structure. When (m)PLA: (m)PP was 8:2, microor- of PLA and PP. However, as PLA is a semicrystalline polymer ganisms on the slices surface were second level of growth with a low crystallization rate, narrow processing window, as after 28 days which showed that the slices has a good biode- well as high hardness and poor process thermal stability, it has gradable performance. limited application in nonwoven fabrics. As a result, research attention has been focused on improving its performance (Lin- nemann et al., 2003; Graupner et al., 2009). Suesat et al. (2003) studied PLA/LLDPE blends and found that blending PLA with 1 Introduction LLDPE remarkably improved the toughness of PLA. Matsuna- ga et al. (2012) prepared spun-bonded nonwoven fabrics using Nonwoven fabric is a new type of advanced material, which PLA/PBS blends and observed an improvement in the tough- has advantages of high performance, short process flow, low ness of PLA nonwoven fabrics. cost, high production, rapidly update on varieties as well as widely available raw material sources, among others. It has significant market prospects and can be widely used in textile, health care, agriculture, construction as well as in fields of high-tech equipment and others. The major techniques to pre-

* Mail address: Li-Sha Pan, Key Laboratory of Advanced Materials of Tropical Island Resources of Ministry of Education, Institution of Materials and Chemical Engineering, Hainan University, Hai- A) B) kou 570228, Hainan, PRC E-mail: [email protected] Fig. 1. Molecular structures of PLA and PP, A) PLA, B) PP

634 Ó Carl Hanser Verlag, Munich Intern. Polymer Processing XXXIII (2018) 5 L.-S. Pan et al.: Preparation and Characterization of Biodegradable Spun-Bonded Nonwoven Fabric Slices

Currently, there are a few reports on the melt blending of mixing machine with an LH60 mixer with different ratio of PLA and PP for preparing biodegradable spun-bonded non- raw materials, blending temperature, blending time, and screw woven fabrics. However, there is no systematic research on speed. the influence of processing techniques on the performance The blended fabric slices were cooled at room temperature of PLA/PP nonwoven fabrics. Spun-bonded nonwoven fab- after melt-blending and stored in desiccators. Then, the rics have many advantages that are of significant research blended fabric slices were pressed by XLB25-D vulcanizing interest, such as low cost, short processing flow, and widely machine under 1908C and 10 MPa to make the plates. available raw material sources. Research on biodegradable Next, the plates were cut into dumbbell-shaped plates PLA/PP spun-bonded nonwoven fabrics can provide not (4 mm · 75 mm). The slices and dumbbell-shaped plates were only a theoretical basis and basic data for the preparation dried for subsequent testing and characterization. of biodegradable nonwoven fabrics with good overall performance, but also has significant social and economic values. In this paper, biodegradable PLA/PP spun-bonded nonwo- 2.3 Performance Tests and Characterization ven fabric slices were prepared by melt blending (Ke et al., 2012).The influence of the ratio of raw materials, blending 2.3.1 Tensile Test temperature, blending time, and screw speed on the mechanical and melt flow properties of the slices was investigated. The ef- The tensile strength of the dumbbell-shaped plates was evalu- fect of the PLA/PP ratio on the thermal properties and mor- ated according to the Chinese Standard GB 1040-92 using a phology of slices was also investigated. The processing condi- tensile tester at 308C and a tensile rate of 50 mm/min. tions were optimized according to the research results, and the biodegradability of the prepared PLA/PP fabric slices was evaluated under optimal processing conditions. 2.3.2 Melt Flow Rate Test (MFR)

2 Experiment MFRs were determined by using a RL-Z1B1 melt flow rate tester. The slices were cut into stripes. A 6 g sample was added 2.1 Reagents and Instruments into the barrel and tested at 190 8C with a 2.16 kg load according to ASTM D1238. 2.1.1 Materials

Polylactic acid (PLA), 6251D, Natural Works, Minnetonka, USA, and polypropylene spun-bonded nonwoven fabric slices, 2.3.3 Differential Scanning Calorimetry Analysis (DSC) HP552R, Basell, Rotterdam, The Netherlands. A 5 mg slices sample was added to the sample cell and purged by high-purity nitrogen. The temperature was increased from 8 8 8 2.1.2 Instruments 0 C to 200 C with an interval of 10 C/min. The DSC en- dothermic peak value was the melting temperature (Tm), and XS-60 rubber plastic mixing machine with an LH60 mixer the midpoint of the heat capacity change was the glass transi- (Shanghai Kechuang Rubber & Plastic Equipment Co., Ltd., tion temperature (Tg). The degree of crystallinity of the slices Shanghai, PRC); swing-type high-speed grinder (RuianYongli XC,DSC can be calculated according to Eq. 1: Pharmaceutical Machinery Co., Ltd., Ruian, PRC); RL- DH À DH Z1B1 melt flow rate tester (Shanghai S.R.D. Scientific Instru- m c ; Xc;DSC ¼ D h ð1Þ ment Co., Ltd., Shanghai, PRC); Q600, Q100 differential scan- H ning calorimeter (DSC) (TA Instruments, New Castle, USA); where DHm is the enthalpy during melting, J/g; DHc is the en- DZF-6020 Series vacuum drying box (Shanghai Boxun Indus- thalpy of crystallization, J/g; DHh is the theoretical enthalpy try & Commerce Co., Ltd., Shanghai, PRC); XLW intelligent of melting of a 100% crystalline, J/g. It can be calculated on electronic tensile testing machine (Jinan Labthink Instruments the basis of the PLA/PP ratio in the slices. The standard enthal- Co., Ltd., Jinan, PRC); XLB25-D vulcanizing machine py of fusion of PLA is 93 J/g (Garlotta, 2001) and that of PP is (Shanghai Light Industry Machinery Co., Ltd., Shanghai, 209 J/g (Doroudiani et al., 1998). PRC); S-3500 N scanning electron microscope (Hitachi Instru- ments Co., Ltd., Tokyo, Japan).

2.3.4 Thermal Gravimetric Analysis (TGA) 2.2 PLA/PP Fabric Slice Preparation A 5 mg slices sample was added into the sample cell and PLA was dried under vacuum at 608C for 12 h, the vacuum purged with high-purity nitrogen. The temperature was ele- was controlled below 30 Pa during drying. The dried PLA and vated from room temperature to 5008Cby108C/min to obtain PP were pre-mixed at certain proportions by swing-type high- thermal gravimetric (TG) and differential thermal gravimetric speed grinder and then melt-blended by XS-60 rubber plastic (DTG) curves.

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2.3.5 Scanning Electron Microscopy (SEM) Observation the PP content was 20%, the tensile strength of the composite slice was 31.02 MPa, and the melt flow rate was 73.08 g/ A Hitachi S-3500 N scanning electron microscope was em- 10 min, which meets the requirements of spun-bonded fab- ployed to observe the micromorphology of the slices. The rics. Furthermore, in this ratio, 80% of the blend slices can slices were brittle-fractured by liquid nitrogen and coated with be biodegradable. gold. The internal micromorphologies were observed with magnifications of 1000 · and 2000 ·. 3.1.2 Influence of Blending Temperature on Tensile Strength and MFR of the Blends 2.3.6 Biodegradability Analysis The PLA/PP ratio was set at 8:2, melt-blending was per- Slices with dimensions of 5 cm · 5cm· 0.2 mm were dried to formed during 5 min, and a screw speed of 40 min–1. The in- constant weight, and their biodegradability was evaluated ac- fluence of the blending temperature on the tensile strength cording to ISO 846-1997 \Plastics – Evaluation of the action and MFR of the PLA/PP slices was investigated; the results of microorganisms". The test bacteria were Aspergillusniger are shown in Fig. 3. Within the investigated temperature ATCC 6275, Penicilliumfuniculosum CMI 114933, Paecilo- range of 170 to 1908C, the mechanical properties and MFR mycesvariotii ATCC 18502, ScopulariopsisbrevicaulisATCC increased. When the temperature was 1858C, the tensile 9645, Chaetomiumglobosum ATCC 6205. The tested slices strength reached a maximum of 33.32 MPa, and the MFR were divided into three groups: O, I, and S. Group O: control was 75.30 g/10 min. When the temperature was below group, stored at standard temperature and moisture; Group I: 1858C, complete blending of PLA and PP was difficult, there- samples inoculated with microbes and cultivated; Group S: by resulting in poor compatibility between two phases and sterilized samples, stored under the same conditions as those brittleness. Hence, obviously, it was necessary to appropri- in Group I. The samples were cultivated in environments with ately elevate the blending temperature for the complete blend- > 90% RH moisture and 288C. After 28 days, the growing be- ing of PLA and PP. However, when the temperature was havior of fungus was evaluated using a microscope. The eva- above 1858C, PLA underwent degradation, which in turn luation standard is listed in Table 1. leads to a sharp decrease of the molecular weight and fluid re-

3 Results and Discussion

3.1 Influence of Processing Parameters on Tensile Strength and MFR of PLA/PP Composite Slices

3.1.1 Effect of the PLA/PP Ratio on Tensile Strength and Flow of the Blends

Melt-blending was performed at 1808C with the screw speed of 40 min–1 and the blending time of 5 min. The influence of the proportion of raw materials on the tensile strength and MFR of the PLA/PP blends was studied. The results are sum- marized in Fig. 2. Within the evaluation range, along with the increase of PP content, the tensile strength and MFR clearly decreased. For pure PLA, the tensile strength was 48.52 MPa, and the MFR was 85.00 g/10 min. As the PP content in the blends increased, the MFR decreased because the Fig. 2. Effect of the PLA/PP ratio on the tensile strength and MFR of MFR of PP was significantly lower than that of PLA. When the blend

Growth level Evaluation

0 No obvious growth under a microscope 1 Not visible with the naked eye but clearly visible under a microscope 2 Obvious growth observed with the naked eye; 25% of the sample surface is covered 3 Obvious growth observed with the naked eye; < 50% of the sample surface is covered 4 A large amount of growth; over 50% of the sample surface is covered 5 Abundant growth; the entire sample surface is covered

Table 1. Evaluation standard

636 Intern. Polymer Processing XXXIII (2018) 5 L.-S. Pan et al.: Preparation and Characterization of Biodegradable Spun-Bonded Nonwoven Fabric Slices

Fig. 3. Influence of the blending temperature on the tensile strength Fig. 4. Influence of blending time on the tensile strength and MFR of and MFR of PLA/PP slice PLA/PP slice sistance. As a result, the mechanical properties of the PLA/PP slices decreased, while the MFR dramatically increased (Bai et al., 2013).

3.1.3 Influence of Blending Time on the Tensile Strength and Melt Flow Rate of PLA/PP Composite Slices

Melt-blending was performed at 1858C, a screw speed of 40 min–1, and the PLA/PP ratio of 8:2. The influence of the blending time on the tensile strength and MFR of the PLA/PP slices was investigated. The influence of blending time on the tensile strength and MFR of PLA/PP slices was also investigated; the results are shown in Fig. 4. Within the investigated range of 3 to 7 min, the tensile strength first increased and then decreased, while the MFR continuously increased with the increasing blending time. At 4 min, the tensile strength reached Fig. 5. Influence of screw speed on the tensile strength and MFR of a maximum value of 33.64 MPa, and the melt flow rate was PLA/PP slice 74.10 g/10 min. When the blending time was less than 4 min, the raw materials were not fully blended. The continuous high sile strength of the slice reached a maximum value of temperature could lead to the decomposition of PLA and PP if 34.42 MPa, and the MFR was 77.20 g/10 min. When the the processing time is higher than 4 min. The interphase sur- screw speed increased, the PLA and PP molecules blended face was severely destroyed, and the mechanical properties sig- better within the same time, which was beneficial for tensile nificantly decreased. On the other hand, the reduced interac- strength. However, if the screw speed was too high, it either tions between the polymers led to the monotonic increase of destroyed the internal structure of the materials or led to an in- MFR. sufficient intertwist of two types of macromolecules, thereby decreasing the tensile properties (Liu et al., 2013). On the other hand, high speed could result in enhanced capability of 3.1.4 Influence of Screw Speed on the Tensile Strength polymer flow units to undergo thermal motion, which would and Melt Flow Rate of PLA/PP Composite Slices also increase MFR. In summary, by the above investigations, the PLA/PP ratio Melt-blending was performed at 1858C, during 4 min, and a exerted a significant influence on both tensile strength and PLA/PP ratio of 8:2. The influence of the screw speed on MFR of the blend. In addition, when the PLA/PP ratio was con- the tensile strength and MFR of the PLA/PP slices was inves- stant, the blending temperature exerted a greater effect on ten- tigated, the results are shown in Fig. 5. Within the investi- sile strength, while blending time significantly affected MFR. gated range of 20 to 60 min–1, the tensile strength first in- From the overall analysis of mechanical and flow properties, creased and then decreased, while the MFR continuously the processing conditions were optimal when the mass ratio of increased. When the screw speed was set as 50 min–1, the ten- the raw materials was 8:2, the blending temperature was

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1858C, the blending time was 4 min, and the rotation speed 3.2.2 Thermogravimetric Analysis was 50 min–1. The 5% decomposition temperature (T–5 %), 50% decomposition temperature (T–50%), 95% decomposition temperature (T ), and peak temperature of decomposition (T ) for PLA 3.2 Thermal Property Analysis –95% P and PLA/PP blends were calculated; these values are listed in Table 2. The TG and DTG curves of PLA/PP blends with dif- The influence of the mass ratio of the raw materials on the ther- ferent ratios are shown in Fig. 7. With increasing PP content mal properties of the PLA/PP blend was evaluated at PLA/PP in the blends, T gradually decreased, indicating that PLA mass ratios of 100/0, 80/20, 50/50, and 20/80 via DSC and –5% could improve the thermal stability of the blends. When the TGA analyses. mass ratio of PLA and PP was 2:8, two peak decomposition temperatures were observed at 351.28C and 404.28C, respec-

3.2.1 Differential Scanning Calorimetry Analysis

The glass transition temperatures (Tg), melting temperatures (Tm), and crystalline temperatures during cooling(Tcc) of PLA and PLA/PP composite slices are shown in Table 2.The DSC curves of PLA and PLA/PP blends are shown in Fig. 6. The crystallinity of PLA/PP blends are listed in Table 3. From Ta- 8 ble 2, the Tg of PLA was 58.57 C and Tg of PP ranged from 8 8 –50 C to –20 C. With an increase of PP content, the Tg of PLA/PP blends slightly decreased. The drop was smaller than the difference of Tg between PP and PLA, which indicated marginal compatibility of PP and PLA. From Fig. 6 and Ta- ble 3, the exothermic peak of crystallization during cooling gradually decreased by increasing PP loading. Moreover, the increasing PP content could decrease the proportion of un- stable a’ crystal in PLA and increase the crystallinity of the blends as PP is a crystalline polymer. Furthermore, the crystallization of PLA could be induced to some extent. In addition, the Tm and Tcc of PLA/PP blends decreased with increasing PP proportion. As shown in Table 2, the Xc,DSC is increasing with an increase of PP content, therefore, the tensile strength of the slices increases with an increase of PP content. Fig. 6. DSC curves of PLA and PLA/PP blends

PLA/PP Tg Tcc Tm T–5% T–50% T–95% TP 8C 8C 8C 8C 8C 8C 8C

10:0 58.57 97.53 168.37 322.2 356.7 377.6 356.5 8:2 57.99 95.93 168.21 317.8 356.9 378.8 359.5 5:5 56.13 96.09 167.66 313.0 357.1 383.9 360.1 2:8 58.12 94.14 167.08 299.4 378.9 416.4 351.2/404.2

Table 2. Thermal properties of PLA and PLA/PP slices

h D D PLA/PP H Hm Hc Xc,DSC J/g J/g J/g %

10:0 93.00 47.09 29.32 19.11 8:2 116.20 47.84 20.94 23.15 5:5 151.10 63.12 7.85 36.58 2:8 185.80 121.30 7.43 61.29

Table 3. Crystallinity of PLA and PLA/PP blends

638 Intern. Polymer Processing XXXIII (2018) 5 L.-S. Pan et al.: Preparation and Characterization of Biodegradable Spun-Bonded Nonwoven Fabric Slices tively, on the DTG curve. It can be deduced that when the con- PLA/PP mass ratio was 5:5, the particle sizes of the dispersed tent of PP increases to 80%, it is difficult for PP to effectively phase varied widely, and the interface between the two phases combine with PLA caused by their poor compatibility, given was obvious. On the other hand, the cross section became the difference in their polarities. Therefore, two of the peak de- rough, and it was the dispersed phase–continuous phase trans- composition temperatures might be the decomposition tem- formation zone. When the PLA/PP mass ratio was 2: 8, a perature of PP and PLA. \sea-island" structure was observed again, which was attributed to phase inversion. PP became the continuous phase with PLA as the dispersed phase. Comparing Fig. 8A and D with 3.3 Scanning Electron Microscopy (SEM) Observation C and F, PP could disperse better in the PLA matrix as com- pared to the dispersion of PLA in PP, which resulted from The internal microstructures of the PLA/PP composite slices the fact that a blending temperature of 1858C led to the melt- after brittle fracture are shown in Fig. 8. When the PLA/PP ing and dispersing of PP. Overall, the interface between the mass ratio was 8:2, the slices exhibited a typical \sea-island" PLA and PP phases was clear, indicating poor compatibility structure with less depressions and hollows. PP was the dis- of the blend. This was because PLA is a polar semi-crystalline persed phase, while PLA was the continuous phase. PP could material, but PP is a non-polar crystalline material without disperse well in the PLA base and exhibited relatively good any polar group in the molecular structure. Hence, it was dif- compatibility, even the embedding phenomenon. When the ficult for PP to effectively combine with polar polymers due to their poor compatibility, attributed to the difference in their polarities.

3.4 Biodegradability of PLA/PP Composite Slices

Currently, there is no unified testing method for the decomposition of polymers in China. Different conditions have been re- ported, such as enzyme test, composting test, buffer method, and soil test, among others. The PLA/PP composite slices prepared under the optimal processing conditions were sent to Guangzhou Institute of Microbiology for assessment. The report indicated that after 28 days, the growth of microorganisms on the composite slices surfaces were at Level 2 (as shown in Fig. 9), which indicated relatively good biodegradability (test #: WJ20142723).

4 Conclusion

A) 1. Biodegradable PLA/PP spun-bonded nonwoven fabric slices were prepared by melt blending. With the increase of PP content, the tensile strength and MFR of slices decreased. With the increase of blending temperature, blending time, and screw speed, the tensile strength of the slices first increased and then decreased, while the MFR increased gradually. Within the test range, combined with rheology, when the PLA/PP mass ratio was 8:2, the blending temperature was 1858C, the blending time was 4 min, and the screw speed was 50 min–1, the tensile strength of the spun-bonded slices was 34.43 MPa, and the melt flow rate was 77.20 g/10 min. They can meet the requirements of spun-bonded nonwoven fabrics, and the processing conditions were the optimal processing parameters. 2. Along with the increase of PP content, the melt flow rate (MFR) and glass transition temperature (Tg) of the slices decreased; The 50% decomposition temperature (T–50%), 95% decomposition temperature (T–95 %), and peak decomposition temperature (TP) increased; the crystallinity increased. The SEM results indicated that when B) the PLA/PP mass ratio was 8:2, there were less hollows in the slice, and the cross section exhibited a \sea-island" Fig. 7. TG (A) and DTG (B) curves of PLA and PLA/PP blends structure.

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A) B) C)

D) E) F) Fig. 8. SEM of PLA/PP slices, A) m(PLA):m(PP)=8:2 ( · 1000), B) m(PLA):m(PP) = 5:5 ( · 1000), C) m(PLA):m(PP) = 2:8 ( · 1000), D) m(PLA):m(PP) = 8:2 ( · 2000), E) m(PLA):m(PP) = 5:5 ( · 2000), F) m(PLA):m(PP) = 2:8 ( · 2000)

Fig. 9. Evaluation of biodegradability of PLA/PP slices, A) PLA:PP = 8:2 7 days, B) A) B) PLA:PP = 8:2 28 days

3. According to the global standard ISO 846-1997 \Plastics – Doroudiani, S., Park, C. B. and Kortschot, M. T., \Processing and Evaluation of the action of microorganisms", biodegradabil- Characterization of Microcellular Foamed High-Density Poly- " ity was evaluated; the results indicated that after 28 days, the ethylene/Isotactic Polypropylene Blends , Polym. Eng. Sci., 38, 1205–1215 (1998), DOI:10.1002/pen.10289 growth of microorganism on the composite slice surface was Garlotta, D., \A Literature Review of Poly(lactic acid)", J. Polym. En- at Level 2, which indicated relatively good biodegradability. viron., 9, 63–84 (2001), DOI:10.1023/A:1020200822435 Graupner, N., Herrmann, A. S. and Müssig, J., \Natural and Man-Made Cellulose Fibre-Reinforced Poly(lactic acid) (PLA) Composites: An Overview about Mechanical Characteristics and Application References Areas", Composites Part A, 40, 810–821(2009), DOI:10.1016/j.compositesa.2009.04.003 Bai, Y., Run, M., Wang, J., Liu, Y. and Li, G., \Rheology and Influ- Ke, K., Wang, Y., Liu, X. Q., Cao, J., Luo, Y., Yang, W., Xie, B. H. and ences of Molding Temperatures on the Impact Strength of PTT/ Yang, M. B., \A Comparison of Melt and Solution Mixing on the TPEE Blends, Polym. Mater. Sci. Eng., 29, 60–63 (2013), Dispersion of Carbon Nanotubes in a Poly(vinylidene fluoride) Ma- DOI:10.16865/j.cnki.1000-7555.2013.10.014 trix", Composites Part B, 43, 1425–1432 (2012),

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DOI:10.1016/j.compositesb.2011.09.007 Acknowledgements Linnemann, B., Harwoko, M. S. and Gries, T., \Fiber Tables Accord- " ing to P.-A. Koch: Polylactide Fibers (PLA) , Chem. Fibers Int., The authors would like to thank the Hainan Province Research 6, 426–433 (2003) Liu, H. H., Pan, L. S., Lin, Q., Xu, N., Lu, L. B., Pang, S. J. and Fu, S. B., and Development Project (No.ZDYF2016016), and the Open \Preparation and Characterization of Poly(propylene carbonate)/ Project Program of Key Laboratory of Advanced Materials of Polystyrene Composite Films by Melt-Extrusion Method", e-Poly- Tropical Island Resources (Hainan University), Ministry of mers, 10, 390–398 (2013), DOI:10.1515/epoly.2010.10.1.390 Education (AM2017-26), and the National Natural Science \ Madhavan Nampoothiri, K., Nair, N. R. and John, R. P., An Overview Fund of China (51663010), for their financial support. This of the Recent Developments in Polylactide (PLA) Research", Bior- esour. Technol., 101, 8493–8501 (2010), PMid:20630747; study was also supported by the Hainan Provincial Fine Chem- DOI:10.1016/j.biortech.2010.05.092 ical Engineering Research Center, the Analytical and Testing Matsunaga, A., \Biodegradation Behavior of a Sheath/Core Type of Center of Hainan University. Bi-Component Spun Bond Nonwovens Made from Poly(butylene succinate)/Poly(lactic acid)", Journal of the Society of Fiber Date received: August 10, 2017 Science and Technology, 68, 218–224 (2012), DOI:10.2115/fiber.68.218 Date accepted: December 25, 2017 Suesat, J., Phillips, D. A. S., Wilding, M. A. and Farrington, D. W., \The Influence of Yarn-Processing Parameters on the Tensile Prop- erties and Structure of Poly(l-lactic acid) Fibres", Polymer, 44, 5993–6002 (2003), DOI:10.1016/S0032-3861(03)00547-0 Yang, X. D., Ding, X., Xue, Y. L. and Jiang, Y. X., \Ageing Perfor- Bibliography mances of Polypropylene Geotextiles under Outdoor Environment DOI 10.3139/217.3562 Conditions", Journal of Donghua University, 33, 57–61 (2007), Intern. Polymer Processing DOI:10.3969/j.issn.1671-0444.2007.01.012 XXXIII (2018) 5; page 634–641 ª Carl Hanser Verlag GmbH & Co. KG ISSN 0930-777X

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