Zonglin Li

Mechanical properties, miscibility, thermal stability, and rheology of poly(propylene carbonate) and poly(ethylene-co-vinyl acetate) blends

Biodegradable polymeric blends are expected to be widely used by industry due to their environmental friendliness and comparable mechanical and thermal properties. In this study, blends of poly(propylene carbonate) (PPC) and poly(ethylene-co-vinyl acetate) (EVA) were prepared. Fourier transform infrared (FTIR) analysis revealed that there were some possible specific interactions between PPC and EVA. The differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) results showed a single temperature peak of Tg between that of pure PPC and that of pure EVA, which suggested that PPC and EVA were compatible. Because of the interfacial interaction between PPC and EVA, EVA could greatly improve the tensile strength, the glass transition temperature and the thermal stability of PPC matrix. Rheological investigation demonstrated that there was a significantly dependence of viscosity on composition. When the EVA content increased, the viscosity began to increase. The PPC/EVA blends could be used as a common biodegradable material for a wide application.

Rheology, mechanical properties and crystallization behavior of glycidyl methacrylate grafted poly(ethylene octene) toughened poly(lactic acid) blends

Poly(lactic acid) (PLA)/poly(ethylene octene) grafted with glycidyl methacrylate (POE-g-GMA denoted as GPOE) blends were prepared via simple melt compounding method at GPOE loadings from 5 to 20wt%. GPOE can significantly affect the physical properties of PLA. Compared to neat PLA, the elongation at break and impact strength of the blends were significantly improved. Scanning electron micrograph analysis revealed large numbers of cavities in the fracture surface of the blends, and the size of the cavities increased along with the increase of GPOE content in the PLA/GPOE blends. Furthermore, the overall crystallization rates were faster in the PLA/GPOE blends than that in neat PLA. However, the crystallization mechanism and crystal structure of these blends remained unchanged despite the presence of GPOE. The addition of GPOE decreased the degree of crystallinity of PLA. The toughened PLA could be of great use and importance for wider practical applications.

The effect of MDI on the structure and mechanical properties of poly(lactic acid) and poly(butylene adipate-co-butylene terephthalate) blends

In this work, poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT 50/50) were melt-blended in the presence of 4,4′-methylene diphenyl diisocyanate (MDI) which acted as a reactive chain extender. The mechanical properties, phase morphology, thermal behavior and crystalline structure of the blends were investigated. Fourier transform infrared measurements revealed that some remarkable chemical interaction had taken place between the two polymers and MDI. Upon increasing the content of MDI, the blends showed increased tensile strength and elongation at break. With the addition of 0–2 wt% MDI, the impact strength of PLA/PBAT-MDI blends increased from 7.0 kJ m−2 to 70.0 kJ m−2. A large shift towards each other in terms of the glass transition temperature was observed by DMA and DSC analysis. SEM micrographs showed not only a reduction in the PBAT phase size but also a significant increase in interfacial adhesion between the PLA and PBAT phases with increasing of MDI. Furthermore, the toughening mechanism of the oriented samples was confirmed by wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) images; it was possible for the smaller crystallites of blends to form during the course of chain extension.

Effect of crystallinity on the thermal conductivity of poly(3-hydroxybutyrate)/BN composites

In this research, boron nitride (BN) acting as both nucleating agent and thermally conductive filler was melt-mixed with poly(3-hydroxybutyrate) (PHB). It was assumed that the introduction of BN not only formed thermally conductive pathways to increase the thermal conductivity of PHB, but also reduced the interfacial thermal resistance due to the interaction between BN and PHB. The assumption was confirmed by density test, morphological observation, and rheological tests. Besides, the introduction of BN improved the thermal stability of PHB, as well. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3,4HB) was introduced as a comparison with PHB to illustrate the effect of crystallinity on the thermal conductivity of PHB/BN composites. According to the DSC tests, BN was proved to be a good nucleating agent for both PHB and P3,4HB. As the wide-angle X-ray diffraction analysis results showed that the crystal structure of PHB/BN and P3,4HB/BN composites was the same, the reason that the thermal conductivity of PHB/BN composites was higher than that of P3,4HB/BN composites at all BN levels was mainly because of the difference of the degree of crystallinity.

High-performance biodegradable polylactide composites fabricated using a novel plasticizer and functionalized eggshell powder

A novel polyester poly(diethylene glycol succinate) (PDEGS) was synthesized and evaluated as a plasticizer for polylactide (PLA) in this study. Meanwhile, an effective sustainable filler, functionalized eggshell powder (FES) with a surface layer of calcium phenyphosphonate was also prepared. Then, PLA biocomposites were prepared from FES and PDEGS using a facile melt blending process. The addition of 15 wt% PDEGS as plasticizer showed good miscibility with PLA macromolecules and increased the chain mobility of PLA. The crystallization kinetics of PLA composites revealed that the highly effective nucleating FES significantly improved the crystallization ability of PLA at both of non-isothermal and isothermal conditions. In addition, the effective plasticizer and well-dispersed FES increased the elongation at break from 6% of pure PLA to over 200% for all of the plasticized PLA composites. These biodegradable PLA biocomposites, coupled with excellent crystallization ability and tunable mechanical properties, demonstrate their potential as alternatives to traditional commodity plastics.

Porous poly(l-lactic acid) sheet prepared by stretching with starch particles as filler for tissue engineering

Porous poly(L-lactic acid) (PLLA) sheets were prepared by uniaxial stretching PLLA sheets containing starch filler. Here, the starch filler content, stretching ratio, stretching rate and stretching temperature are important factors to influence the structure of the porous PLLA sheets, therefore, they have been investigated in detail. The pore size distribution and tortuosity were characterized by Mercury Intrusion Porosimetry. The results revealed that the porosity and pore size enlarged with the increase of the starch filler content and stretching ratio, while shrank with the rise of stretching temperature. On the other hand, the pore structure almost had no changes with the stretching rate ranging between 5 and 40 mm/min. In order to test and verify that the porous PLLA sheet was suitable for the tissue engineering, the starch particles were removed by selective enzymatic degradation and its in vitro biocompatibility to osteoblast-like MC3T3-E1 cells was investigated.