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A functionalized high-density polyethylene (HDPE) with maleic anhydride (MAH) was prepared using a reactive extruding method. This copolymer was used as a compatibilizer of blends of polyamide 6 (PA6) and ultrahigh molecular weight polyethylene (UHMWPE). Morphologies were examined by a scanning electron microscope. It was found that the dimension of UHMWPE and HDPE domains in the PA6 matrix decreased dramatically, compared with that of the uncompatibilized blending system. The size of the UHMWPE domains was reduced from 35 m (PA6/UHMWPE, 80/20) to less than 4 m (PA6/UHMWPE/HDPE-g-MAH, 80/20/20). The tensile strength and Izod impact strength of PA6/UHMWPE/HDPE-g-MAH (80/20/20) were 1.5 and 1.6 times as high as those of PA6/UHMWPE (80/20), respectively. This behavior could be attributed to chemical reactions between the anhydride groups of HDPE-g-MAH and the terminal amino groups of PA6 in PA6/UHMWPE/HDPE-g-MAH blends. Thermal analysis was performed to confirm that the above chemical reactions took place during the blending process.

Blends of linear low-density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high-impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl 3 ), was adopted to initiate the Friedel-Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl 3 blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel-Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE-g-PS and LLDPE-g-HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m 2 . Scanning electron microscopy micrographs showed that the size of the domains decreased from 4 -5 to less than 1 m, depending on the content of added AlCl 3 . The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt-flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending.

Grafting of acrylic acid and glycidyl methacrylate onto low density polyethylene (LDPE) was performed by using a corotating twin-screw extruder. The effects of residence time and concentration of initiator and monomers on degree of grafting and gel content of grafting LDPE were studied systematically. Paraffin, styrene, p-benzoquinone, triphenyl phosphite, tetrachloromethane, and oleic acid were added to try to decrease the extent of crosslinking of LDPE. 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy (4-hydroxyl-TEMPO) and dipentamethylenethiuram tetrasulfide were also tried to inhibit crosslinking reaction of LDPE during its extruding grafting process. It was found that p-benzoquinone, triphenyl phosphite and tetrachloromethane were good inhibitors for crosslinking of LDPE.

The PP/PP-g-PS/SEBS blends are prepared by melt extrusion in order to improve both insulating properties and toughness of PP. SEBS is used to reduce the rigidity of PP, while the insulating properties are improved by adding PP-g-PS without decreasing mechanical properties. The microstructure of PP blends is carefully investigated by SEM, DMA, XRD, and DSC. It is interesting to find that a core–shell dispersion phase formed in the blend with the adding of PP-g-PS, and the size of core is decreased while the thickness of shell is increased with further increasing volume of PP-g-PS. Due to this special structure, the nucleation ability of SEBS is decreased. Meanwhile, the rigid segments and compatibilization effect of PP-g-PS not only increased the glass transition temperature of both PP and SEBS, but also enhanced their adhesion. Therefore, the electrical properties were increased without decreasing the mechanical properties of the blends. Consequently, an insulation material with excellent mechanical properties was obtained.

ABSTRACT:The chain structure, spherulite morphology, and rheological property of LL-DPE-g-AA were studied by using electronspray mass spectroscopy, 13 C-NMR, and rheometer. Experimental evidence proved that AA monomers grafted onto the LLDPE backbone formed multiunit AA branch chains. It was found that AA branch chains could hinder movement of the LLDPE main chain during crystallization. Spherulites of LLDPE became more anomalous because of the presence of AA branch chains. Rheological behavior showed that AA branch chains could act as an inner plasticizer at the temperature range of 170-200°C, which made LLDPE-g-AA easy to further process.

The voltage stabilizers can effectively improve DC breakdown strength of polyolefin, but its precipitation from polymer matrix inhibits its application. To address this problem, we prepared a reactive voltage stabilizer 4-acryloxy acetophenone (AAP) and employed a simple strategy of grafting it onto the LLDPE backbone to maintain polyolefin at a high DC breakdown strength level for a long time. The DC breakdown strength of thermal-treated samples at 60 °C for different periods was measured. It was found that the grafting samples performed much higher DC breakdown strength than that of neat LLDPE and blending samples after accelerated migration at 60 °C. SEM images demonstrated lower AAP precipitation on the surface of grafting samples. The purified grafting samples also exhibited high DC breakdown strength, which means the AAP can be maintained via grafting onto strategy. Meanwhile, the rheological results showed good processability of the grafting samples.

A solvent-assisted diffusion method is developed here to prepare thermally conductive epoxy composites (EP) after hexagonal boron nitride (h-BN) was modified via poly (vinyl benzal) (PVB) noncovalent bond coating. The h-BN@ PVB with different PVB coating contents was prepared and verified by FT-IR, SEM, and TGA. Then, EPs loaded with 20 wt % filler were prepared by using these different PVB-coated particles to find the optimum value for PVB content. Finally, when introduced dimethyl sulfoxide solvent to the dissolve PVB shell after the dispersion of h-BN@PVB into epoxy resin, the thermal conductivities were similar to that of h-BN/EP at low filler levels, but larger at high filler loading because of the formation of flower-like thermal conduction paths. The thermal conductivity can reach 0.89 W m −1 •K −1 at 40 wt % h-BN@PVB loading by using the solvent-assisted diffusion method, which is 4 times higher than that of native epoxy resin.