Modification of Poly(lactic acid) by Blending with Chain Extender.pdf

1、Significant pollution as a result of industrial expansion in all areas turns scientists recently to reduce these risks. It was found that the process of plastic wastes buried in the soil is unable to eliminate, because t

2、hey are not biodegradable in the soil. In addition the process of burning plastic wastes causes air pollution due to emissions;this leads to environmental and waste-management problems. As a result of these problems, a l

3、ot of attention has been focused on biodegradable polymers both in academia and industry. Poly(lactic acid) (PLA) is one of linear aliphatic thermoplastic polyesters with outstanding advantages over other polymers. It’s

4、derived from renewable and degradable resources with good biocompatibility, excellent transparency non-toxic byproducts and high strength and modulus.
　　It is well known that the molecular weight reduction and weight

5、loss caused by both hydrolysis and depolymerization reaction result in poor mechanical performance of final products. In this study, oligomer JoncrylTM ADR was used to extend the chains and improve the mechanical propert

6、ies. The chain extender multifunction epoxide was used with concentrations of 0.5wt％, 0.7wt% and 0.9wt%, respectively. The structure, molecular weight, thermal properties, and rheological properties were studied in order

7、 to provide a theoretical basis for the determination of melt-spinning process. The effects of spinning conditions on the crystalline morphology, molecular orientation, mechanical properties, thermal properties, moisture

8、 absorption and surface morphology were evaluated.
　　Three different types of JoncrylTM ADR chain extenders named as ADR, ADR-1 and ADR-2 were blended with PLA at various concentrations 0.5wt%, 0.7wt% and 0.9wt%, resp

9、ectively. properties, ADR has been chosen as a blending material due to the lower melt flow index and excellent mechanical properties.
　　The FT-IR spectra of Joncryl CE showed three peaks approximately at 842, 90

10、8, and 1255cm-1, respectively, which can be ascribed to the C-O stretching modes of the epoxy groups. However, these peaks became weaker or almost disappeared in the case of PLA/CE blends, due to the interaction of the e

11、poxy groups with carboxyl groups on PLA.
　　According to GPC experiment, the molecular weight (Mw) of the PLA/CE blends tended to increase when increasing the chain extender content. Furthermore, the addition of chain

12、extender led to improvement on intrinsic viscosity which accompanied by a remarkable increase in the viscosity–average molecular weight. On other hand, the melt flow index results of the PLA/CE blends tended to decrease

13、when increasing the content of CE, which could be attributed to improvement in the molecular weight. From GPC, MFI and viscosity results clearly, there is an increase in the molecular weight resulted from the coupling be

14、tween epoxy groups of CE and end groups of PLA, as confirmed by FTIR result.
　　TGA results showed that the PLA/CE blends possessed the quicker degradability than that of PLA-0.0%. The DSC results showed that Tg shifte

15、d to the higher temperature and Tm increased slightly after adding chain extender as well as, the crystallinity of modified PLA decreased when increasing the content of the chain extender.
　　The rheological properties

16、 of PLA and PLA/CE blends showed that the addition of CE resulted in gradual increase in the G' and G"which indicated to further increased entanglement density. Moreover, it could be seen that there is a noticeable effec

17、t of the chain extender addition on the PLAs viscosity. The viscosity of the blend clearly increased with adding the CE.
　　Multifilament was successfully spun on a laboratory-scale single screw melt-spinning unit. The

18、 multifilament obtained was drawn on a parallel drawing machine at temperature of 75℃ and DR = 3. According to WAXD results, the introduction of chain extenders led to improve the crystallinity, exactly 39.38%, 44.85%, 5

19、4.24 and 55.21 for PLA-0.0%, PLA-0.5%, PLA-0.7% and PAL-0.9% fibers respectively, and that could be attributed to increase in the degree of molecular chains ordering of PLA/CE fibers. The orientation factors (f0) of

20、 PLA/CE fibers were found to increase continuously with the take-up speed and the chain extender content.
　　The DSC results of PLA-0.0% and PLA/CE fibers showed that the Tm slightly increased, while Tg showed no consi

21、derable variation with the chain extender. Moreover, all fibers showed higher Tg than the pellets after spinning; this might be resulted from the improvement of molecular orientation along the drawing direction and more

22、ordered crystalline during process. On the other hand, the crystallinity of PLA/CE fibers increased when increasing the content of the chain extender. These results were consistent with the XRD results.
　　It was found

23、 that the tensile strength and modulus of the PLA/CE fibers were gradually increased with CE content. These results suggest that the introduction of chain extenders have a positive influence on the mechanical properties

24、of PLA fibers. In addition to, the tensile strength and modulus were increased with the increase of take-up speed from 300 m/min to 400 m/min, this increment could be attributed to the improvement of molecular orientatio

25、n along the drawing direction as well as, more ordered crystalline during process.
　　It was found that the moisture regain of PLA/CE fibers significantly decreased, which indicating the possible reaction between CE an

26、d PLA led to reduction the carboxyl group after chain extension as well as, maybe more crystallinity of PLA/CE fibers decline the moisture regain.
　　The SEM result showed clear and smooth surface morphology, this may