Zhizhong Su

Phase Structure of Compatibilized Poly(Lactic Acid)/Linear Low-Density Polyethylene Blends

Blends of PLA and linear low-density polyethylene (LLDPE) were compatibilized with glycidyl methacrylate (GMA)–grafted poly(ethylene-octene) copolymer (mPOE). Effects of compatilizer on phase structure of compatibilized PLA/LLDPE were studied by spreading coefficient calculation prediction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) analysis. The spreading coefficient calculations, based on experimental and calculated surface tension data, show that mPOE spreads on LLDPE extensively to encapsulate LLDPE completely, which is in good agreement with the results of DSC, SEM, and WAXD analysis. The chemical reaction between the end carboxyl groups or end hydroxyl groups of PLA and epoxy groups of mPOE, which is suggested as the driving force leading to an ideal interfacial adhesion between PLA and the dispersed phase, was confirmed by Fourier transform infrared ray (FT-IR) spectroscopy analysis.

Crystallization Behavior of Poly(Lactic Acid) Filled with Modified Carbon Black

A novel method was employed to modify the surface of carbon black (CB) by an organic small molecule in a Haake Rheomix mixer. The modified carbon black (MCB) was dispersed uniformly in poly(lactic acid; PLA). The crystallization behaviors of PLA, PLA/CB and PLA/MCB composites were investigated by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and polarizing optical microscopy. It is found that the addition of CB or MCB can influence the crystallization behavior of PLA. PLA/MCB has a faster crystallization rate and higher crystallization peak temperature than PLA/CB. For non-isothermal studies, Jeziorny and Mo equations were employed. The Mo equation can well describe the non-isothermal crystallization of the three samples. For PLA/CB and PLA/MCB composites containing 3wt% fillers, the nucleating activity for CB is about 0.32, and about 0.16 for MCB. All these results show that MCB is an effective nucleating agent. PLA/MCB has a higher nucleation rate than PLA/CB because of the finer dispersed particles size and improved interaction between MCB and PLA.

Reactive Compatibilization and Properties of Recycled Poly(ethylene terephthalate)/Poly(ethylene-octene) Blends

High toughness recycled poly(ethylene terephthalate) (R-PET)/poly(ethylene-octene) (POE) blends were prepa scanning electron microscopy red by adding glycidyl methacrylate grafted poly(ethylene-octene) (mPOE) as reactive compatibilizer. Evidence for reaction between the carboxyl or hydroxyl end groups of R-PET and the epoxy groups of mPOE under the conditions of processing to form graft copolymers (PET-g-mPOE) is presented. Effects of compatibilizer on morphology and mechanical and thermal properties of the blends were evaluated systematically. The results showed that dispersed phase particle size decreased with increasing mPOE content until the critical compatibilizer concentration (5 wt%) was reached. Notched Charpy impact strength and elongation at break were improved greatly by the addition of compatibilizer. Differential scanning calorimetry (DSC) analysis showed POE could act as a nucleating agent in the R-PET matrix to improve the crystallization temperature, while the graft copolymers formed in compatibilized R-PET/POE blends decreased the nucleation activity.

Nonisothermal Crystallization of Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl methacrylate grafted poly(ethylene octene) (mPOE). The nonisothermal crystallization behavior of r-PET, r-PET/POE, and r-PET/mPOE blends was investigated using differential scanning calorimetry (DSC). The crystallization peak temperatures (T p ) of the r-PET/POE and r-PET/mPOE blends were higher than that of r-PET at various cooling rates. Furthermore, the half-time for crystallization (t 1/2 ) decreased in the r-PET/POE and r-PET/mPOE blends, implying the nucleating role of POE and mPOE. The mPOE had lower nucleation activity than POE because the in situ formed copolymer PET-g-POE in the PET/mPOE blend restricted the movement of PET chains. Non-isothermal crystallization kinetics analysis was carried out based on the modified Avrami equation, the Ozawa equation, and the Mo method. It was found that the Mo method provided a better fit for the experimental data for all samples. The effective energy barriers for nonisothermal crystallization of r-PET and its blends were determined by the Kissinger method.

Morphology and Properties of Injection-Moulded Recycled Poly(Ethylene Terephthalate)/Poly(Ethylene Octene) Blends

Recycled poly(ethylene terephthalate) (r-PET) was blended with poly(ethylene octene) (POE) and glycidyl-methacrylate-grafted poly(ethylene octene) (mPOE). The morphology and thermal properties of injection-moulded blends through the thickness of impact specimens were investigated. A remarkable difference was found in the through-thickness morphology and thermal properties of the injection-moulded blends. The three-layered structure (namely the skin, subskin, and core layers) showed a hierarchical structure. Scanning electron microscopy showed that the orientation of the dispersed-phase particles in the skin and subskin layers was much higher than that in the core layer. Differential scanning calorimetry indicated that the skin and core layers had the same component content, but the core layer had a higher degree of crystallinity than the skin layer.