Gance Dai

Influence of functionalized polyolefin on interfacial adhesion of glass fiber-reinforced polypropylene

Several types of functionalized polyolefins, grafted with maleic anhydride, were synthesized and used to modify the surface of fiberglass in reinforced polypropylene composites. The influence of maleated polyolefin, matrix, and compounding conditions on the interfacial bonding strength of composite were studied by measuring interfacial shear strength. The results showed that strong interactions, e.g., chemical bonding, were formed between maleated polyolefin and fiber surface. When the modified fibers were compounded with polypropylene, firm entanglements of molecular chain were formed due to the segmental interdiffusion between maleated polyolefin and matrix polypropylene. As a result, the degree of fiber-matrix adhesion was improved. The extent of such improvement depended on the grafting degree, chain length of maleated polyolefin, and the compatibility between maleated polyolefin and matrix resin. At the same time, the compounding temperature and the cooling procedure affected the interfacial adhesion too.

Studies on Mechanical Properties of Discontinuous Glass Fiber/Continuous Glass Mat/Polypropylene Composite

The mechanical properties of discontinuous glass fiber/continuous glass fiber mat/polypropylene composites were investigated. The mechanical properties increased with increasing areal weight of the continuous glass mat, whereas the suitable content of discontinuous fiber was also depended on the mat areal weight. The impact strength of composites initially decreased due to the addition of discontinuous glass fiber, but increased when the content of discontinuous glass fiber further increased. Comparisons between the 4 mm discontinuous fiber length and the 12 mm fiber showed that the longer discontinuous glass fiber was advantageous to the mechanical properties of composite system. The modification of the interfacial adhesion between reinforcements and matrix resin by using functionalized polypropylene played a significant role in improving the mechanical properties of the composites. But the impact strength decreased above 5% of MA-g-PP level (with respect to matrix resin). It was also found that using a matrix resin with a high melt index was beneficial impregnation with the mechanical properties improving accordingly.

Polypropylene/Ethylene-Octene Copolymer/Organic-Montmorillonite Nanocomposites

Melt compounding was employed to prepare polypropylene (PP)/ethylene-octene copolymer (POE)/organic-montmorillonite (OMMT) nanocomposites. Polypropylene grafted with maleic anhydride (MPP) was added as a compatibilising agent. Analyses by wide-angle X-ray diffraction, transmission electron microscopy and scanning electron microscopy indicated that polymer chains intercalated into OMMT and that some of the OMMT delaminated into nano-layers dispersed in the PP matrix. Mechanical tests showed that the addition of POE increases the toughness of PP, but it decreases the stiffness. When OMMT and MPP were added, the toughness of PP increased greatly and the stiffness was not changed profoundly. Differential scanning calorimetry was used to study the melt and crystallization behavior of the composites. The results indicate that OMMT and MPP act as effective nucleating agents.

Effect of flexible polymer coating on interfacial adhesion of glass fibre reinforced polypropylene

Polymer coatings were obtained by using two rubbers, cis-polybutadiene rubber and ethylene-propylene diene monomer and two block copolymer: polystyrene-block-polybutadiene-block-polyvinyltriethoxysilane and polystyrene -block-polyvinyltrietho xysilane. They were used to coat glass fibre surfaces. The effects of the coatings on the interfacial adhesion and thermal cycling resistance of composites were studied by a single-filament fragmentation technique designed to measure the interfacial shear strength of glass fibre reinforced polypropylene. The interfacial shear strength was improved by the rubber coatings, which could graft to silane coupling agents coated onto the fibre surfaces, and could undergo crosslinking under peroxide initiation. The interfacial bond strength was determined by the nature and thickness of the rubber coatings. The interfacial adhesion was also improved when using block copolymers to treat glass fibres. The rubbers and those copolymers having flexible blocks in their chain structures both produced coatings that could relieve the thermal stresses at the composite interface during temperature cycling. The interface between the composites and the flexible polymer coatings had good thermal cycling fatigue resistance.