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ABSTRACT:The reactive extrusion of maleic anhydride grafted polypropylene (PP-g-MAH) with ethylenediamine (EDA) as coupling agent is carried out in a corotating twin-screw extruder to produce long chain branched polypropylene (LCBPP). Part of PP-g-MAH is replaced by maleic anhydride grafted high-density polyethylene (HDPEg-MAH) or linear low-density polyethylene (LLDPE-g-MAH) to obtain hybrid long chain branched (LCB) polyolefins. Compared with the PP-g-MAH, PE-g-MAH, and their blends, the LCB polyolefins exhibit excellent dynamic shear and transient extensional rheological characteristics such as increased dynamic modulus, higher low-frequency complex viscosity, broader relaxation spectra, significantly enhanced melt strength and strain-hardening behaviors. The LCB polyolefins also have higher tensile strength, tensile modulus, impact strength and lower elongation at break than their blends. Furthermore, supercritical carbon dioxide (scCO 2 ) is constructively introduced in the reactive extrusion process. In the presence of scCO 2 , the motor current of the twin extruder is decreased and LCB polyolefins with lower melt flow rate (MFR), higher complex viscosity and increased tensile strength and modulus can be obtained. This indicates that the application of scCO 2 can reduce the viscosity of melt in extruder, enhance the diffusion of reactive species, and then facilitate the long chain branching reaction between anhydride group and primary amine group.

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Polybutadiene (PB) is used to fill an oil absorption resin as a physical crosslinker to construct a kind of 3-dimensional network with a high degree crosslinking and low crosslink density. A series of acrylic resin particles with various compositions are prepared by suspension polymerization, using benzoyl peroxide (BPO) as an initiator and ethylene glycol dimethacrylate (EGDMA) as a chemical crosslinker. The effects of the polymerization temperature, initiator concentration, monomer feed ratio, and chemical and physical crosslinker concentrations on the oil absorbency and gel fraction (degree of crosslinking) are studied. The recipe and operation conditions are optimized as follows: a mass ratio of 3:1 for styrene (St)/dodecyl methacrylate or St/butyl acrylate, 0.5 wt % BPO, and 80°C for 7-8 h. The effect of the physical crosslinker (PB) concentration is complex. The oil absorbency increases with increasing PB at lower EGDMA concentrations. However, under this same condition, particles cannot be formed if the PB concentration is higher than a certain value. By contrast, there is an optimum PB concentration when the EGDMA concentration is higher. The oil absorption speed is also investigated. The presence of PB can speed up absorption.

Poly(vinyl chloride)/layered double hydroxides (PVC/LDHs) composite resins were prepared by in situ suspension polymerization of vinyl chloride monomer in the presence of LDHs intercalated with dodecyl sulfate anions (LDH-DS), and were further processed to obtain PVC/ LDH-DS nanocomposites. It was found that the mean particle size of PVC composite resins decreased as LDH-DS was added in the polymerization system. The 5 and 10% weight loss temperatures of PVC resins significantly increased with the increase of LDH-DS weight fraction in the composite resins. The transmission electron microscopy images showed that LDH-DS particles were partially intercalated and partially exfoliated, and well distributed in the PVC nanocomposites. The storage modulus below the glass transition region and the glass temperature of the PVC/LDH-DS nanocomposites are greater than that of the pristine PVC. The mechanical properties of PVC/LDH-DS nanocomposites indicate that LDH-DS nanoparticles stiffen and toughen PVC. The tensile strength, Young's modulus, and Charpy notched impact strength of the PVC/LDH-DS nanocomposites are greater than those of the pristine PVC and PVC/ LDH-DS composites prepared by the melt blending.