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Polylactic acid (PLA)/polybutylene succinate (PBS) and the PLA/PBS/montmorillonite (MMT) composites were prepared by melt extrusion. The morphology structure, mechanical, thermal, and dynamic rheological properties of the composites were characterized, as well as foaming extrusion behavior of the composites was also studied. The results showed that MMT particles were intercalated into the PLA/PBS matrix forming an ‘intercalation’ structure. The toughness of PLA could be improved by blending with PBS. The comprehensive evaluation of mechanical properties of PLA/PBS was further improved by adding MMT. MMT could play the role of heterogeneous nucleation to improve the crystallization effect of PLA/PBS composite. The melt strength of PLA could be significantly increased by the synergies of MMT and PBS. Meanwhile, MMT could act as a compatibilizer to enhance the interfacial interaction between PLA and PBS. The synergies of PBS and MMT effectively reduced the density of PLA blend foam products, and increased their cell density, uniformity of cell size, and shape distribution.

Chain extension was an effective method for increasing the molecular weight, the melt strength and the foaming property of linear polymer. In this paper, pyromellitic dianhydride (PMDA) was used as chain extender to improve these properties of linear poly (ethylene terephthalate) (PET). The intrinsic viscosity, rheological and thermal characterizations of various PET samples was investigated. The results demonstrated that the increasement of the viscoelasticity at low frequencies was correlated to the raise of the intrinsic viscosity and the formation of long chain branching. These structural changes resulted in the decreasement of the crystallization temperature and melt temperature as well as the increase in the cold crystallization values with the increasing content of PMDA. The cellular morphology and expansion ratio of CEPET foams were also obviously improved by the introduction of PMDA. The expansion ratio of CEPET foam with the PMDA content of 1.0 phr would reach 31.78. In addition, the effect of the chain extension reaction time on the intrinsic viscosity, the rheological behavior, and foaming properties of PET were also studied. The results showed that the intrinsic viscosity, the rheological behavior, and the foamability of CEPET also decreased gradually with increasing chain extension reaction time, which should be attributed to the occurrence of more and more intense thermal degradation.

Strain hardening and crystallization behaviors, crystal structure and morphology of linear/long-chain-branching polypropylene blends (LPP/LCBPP) was studied by means of Rheotens, DSC, XRD, and POM. Upon incorporation of LCBPP into LPP, the melt strength and the strain rate durability of the latter were obviously enhanced, the nucleation and overall crystallization rates were increased and crystallization temperature elevated. At some middle fraction of LCBPP, the most remarkably effects were observed. The content of the branched architecture and the entanglement density were considered responsible for these influences.KEY WORDS: Long Chain Branching Polypropylene / Linear Polypropylene / Crystallization Behavior / Crystal Morphology / Commodity isotactic PP possesses many desirable physical properties such as good resistance to chemicals, high stiffness, high rigidity, high service temperature, and good temperature stability compared to other polyolefines. However, the lack of melt elasticity strain hardening behavior has limited its applications in extrusion foaming, extrusion coating, blow molding, and thermoforming, where the extensional flow dominates. [1][2][3][4] In order to improve the melt strength of linear isotactic PP (LPP), many efforts were made aiming at enhancing the strain hardening of LPP melt in extensional flow. Crosslinking, broading the molecular weight distribution, blending with other polyolefin were tried in the early researches. [5][6][7] Since 1990s, the introduction of long chain branching onto the backbone of LPP has been considered an effective approach to achieve the high melt strength. 8,9 A wide variety of methods were employed to achieve the grafting of long-chain side chains onto LPP, including electron-beam irradiation 10-13 and reactive extrusion with a multifunctional monomer and peroxide. 4,[14][15][16][17][18] Several commercial long chain branching polypropylene (LCBPP) grades were also developed. 19 However, LCBPP is more expensive than LPP, for this reason, to blend LPP with LCBPP constituted a practical way to generate a PP material with higher melt strength. The LCBPP introduced not only branching points and long side chains, but also more free volumes into the system. How such factors influence the crystallization and melting behavior and the properties of the melt remained interesting problems. In this work, blends of commercial LPP and LCBPP were prepared and the aforementioned effects were explored. EXPERIMENTAL MaterialsLinear PP (T36F) was obtained from Qilu Petrochemical Co. Ltd. Long chain branching PP (PF814) was purchased from Basell Co. Ltd. The molecular weight and polydispersity of the PPs were shown in Table I. Antioxidant Irganox B225 was provided by Ciba Specialty Chemicals. Preparation of the BlendsSeven blends of T36F/PF814 (LPP/LCBPP) with weight ratios of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 0/100 were melt extruded and pelletized using a co-rotating twin screw extruder (WP-30, former WP company, Germany) at 100 rpm. The blends were stabilized ...

A methodology for the preparation of chain extended poly (ethylene terephthalate) (PET) and its foams by autoclave batching foaming method was proposed. First, PET was mixed with tetraglycidyl diamino diphenyl methane (TGDDM) as chain extender to generate the branching/crosslinking molecular structure and improve the viscoelasticity of PET. Then, PET foams were prepared using supercritical CO2 as physical blowing agent. The molecular structures of various PET samples were characterized by the nuclear magnetic resonance, gelation degree and crosslinking density test. The results showed that with the introduction of TGDDM, the branching/crosslinking structure of PET appeared. The influences of various molecular structures on the thermal property and rheology of PET were also studied. The results showed that the crystallization temperature, crystallization rate, and crystallinity of various PET samples decreased with the content of TGDDM, but the modified PET had higher melt elasticity than that of pure PET. PET foam with the addition of 0.4% TGDDM had finer cellular morphology and the highest expansion ratio.