IntroductionThere are a variety of ways that can be used for crosslinking of polyolefins. These include radiation crosslinking, peroxide crosslinking, and silane-water crosslinking. Among those, peroxide crosslinking is the most widely-used method, especially for crosslinking of polyethylene (PE). In the case of poly(propylene) (PP), it has been well established that PP mainly experiences chain scission reactions during peroxide modification, leading to a decrease in molecular weight and molecular weight distribution. Therefore, in order to perform crosslinking of PP, the silane-water crosslinking seems to be a promising technique.Silane-grafting and water-crosslinking of polyolefins have received much attention in recent years, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] not only for industrial applications but also in fundamental research, because of its various advantages, such as easy processing, low capital investment, and favorable properties in the processed materials. The properties of silane-crosslinked products were reported earlier to differ from those of peroxide crosslinked materials, in which the silane-crosslinked polymers were found to exhibit better thermal stability and higher energy storage capacity. [1] The usual procedure for silane-water crosslinking process is through the preparation of a silane-grafted polymer using a freeradical reaction of peroxides and vinyl alkoxysilane. After shaping into products, the silane-grafted polymer is crosslinked by exposure to a humid environment. The crosslinking reaction involves hydrolysation of the hydrolysable alkoxy groups with moisture, followed by condensation of the formed hydroxyl groups to form stable siloxane linkages, cf. Scheme 1.The vast majority of studies on silane-crosslinking technique are concerned with PE and ethylene copolySummary: The silane-grafting and water-crosslinking of poly(propylene) (PP) and its composites with calcium carbonate are described. Particular consideration is made on the properties and characterization of the grafted-and crosslinked-products. Silane-grafting of the polymers was performed in the melt by the use of vinyltrimethoxysilane and dicumyl peroxide. The results show that during the grafting process, PP chain-scission was accompanied as a side reaction. Peroxide concentration was found to be a major factor in determining the extents of grafting and PP degradation. After conducting a crosslinking reaction, the degree of crosslink determined from the direct measurement of gel content and indirect method by evaluating FTIR data was compared. The effects of silane crosslink on the thermal and mechanical properties of the PP composites were discussed. A combined effect of filler and silane crosslink network in enhancing composite modulus, tensile stress, heat distortion, and decomposition temperatures is evident.Formation of stable siloxane linkages.mers. [1][2][3][4][5][6][7][8][9][10][11][12] Not many studies concerning the crosslinking of PP have been reported. [13][14][15] This is most likely ...

Silane-crosslinkable polypropylene (PP) composites containing calcium carbonate (CaCO 3 ) as a filler have been investigated. The melt grafting of vinyl trimethoxysilane to PP with dicumyl peroxide (DCP) as a radical initiator is demonstrated. The thermal and mechanical properties of the crosslinkable products are also discussed. The results show that two reactions, that is, silane grafting and PP degradation, take place in parallel. The extents of silane grafting and PP degradation strongly depend on the reaction temperature, grafting formulation, and amount of the filler in the systems. Increasing the DCP concentration (up to 0.05 wt %) leads to an increase in the grafting degree. However, when the concentration of radicals is over a certain degree, the dominant reaction is PP chain scission. This results in a drastic decrease in the polymer viscosity. In systems containing both silane and CaCO 3 , the viscosity of the polymer is higher than that of a grafted sample without CaCO 3 addition; in other words, the effect of the filler on the polymer viscosity compensates for the effect caused by PP degradation. Differential scanning calorimetry results show that the crystallization starts earlier for grafted samples. The percentage of the crystallinity of grafted PP is higher than that of the pure polymer. The incorporated silane does not have a strong effect on the mobility of the PP chains, as revealed by dynamic mechanical analysis. In comparison with ungrafted composites, the silane-crosslinkable products show higher tensile stress and modulus.