| dc.description.abstract | The objective of the study is to improve the interfacial adhesion between the wood fibers and thermoplastic matrix. Efforts were also directed towards improving manufacturing processes so as to realize the full potential of wood fibers as reinforcing fillers. Chemical coupling plays an important role in improving interfacial bonding strength in wood-polymer composites. A novel compatibilizer with isocyanate functional group was synthesized by grafting m-Isopropenyl –α –α –dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene using reactive extrusion process. The compatibilizer was characterized with respect to its nature, concentration and location of functional group, and molecular weight.
There are two main process issues when blending polymers with incompatible filler: (1) creating and maintaining the target morphology, and (2) doing so with minimum degradation of fillers. A 28mm co-rotating intermeshing twin screw extrusion system was custom built and the design optimized for (1) blending biological fibers with thermoplastics, and (2) for melt phase fictionalization of thermoplastics by reactive extrusion.
To assess the effect of inclusion of wood fibers in polypropylene composites, a series of polypropylene wood fiber/wood flour filled composite materials having 10 to 50 wt % of wood content were prepared using the co-rotating twin screw extrusion system. m-TMI-g-PP and MAPP were used as coupling agents. Addition of wood fibers, at all levels, resulted in more rigid and tenacious composites. The continuous improvement in properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low modulus polypropylene matrix with the high modulus wood filler. Studies on were also undertaken to understand effect of particle morphology, type and concentration of coupling agent, and effect of process additives on mechanical properties. Composites prepared with m-TMI-grafted-PP were much superior to the composites prepared with conventionally used maleated polypropylene in all the cases.
Non-destructive evaluation of dynamic modulus of elasticity (MoE) and shear modulus of wood filled polypropylene composite at various filler contents was carried out from the vibration frequencies of disc shaped specimens. The vibration damping behaviour of the composite material was evaluated. MoE and shear modulus were found to increase whereas damping coefficient decreased with the increasing filler content.
Knowledge of moisture uptake and transport properties is useful in estimating moisture related effects such as fungal attack and loss of mechanical strength. Hence, a study was undertaken to asses the moisture absorption by wood filled
polypropylene composites. Composites prepared with coupling agents absorbed at least 30% less moisture than composites without compatibilizer. Thermo-gravimetric
measurements were also carried out to evaluate the thermal stability and to evaluate kinetic parameters associated with thermal degradation of wood fiber and wood flour filled polypropylene composites. The moisture absorption and thermal behaviour are described based on analytical models.
High efficiency filler-anchored catalyst system was prepared by substituting of hydroxyl groups present on the cellulosic filler. The process involves immobilizing the cocatalyst onto the cellulosic filler surface followed by addition of metallocene catalyst and then polymerization of ethylene using this filler supported catalyst. The polymerization and composite formation takes place simultaneously. All the polymerization reactions were carried out in a high-pressure stirred autoclave. Effect of temperature, ethylene pressure, and cocatalyst to catalyst ratios (Al/TM ratios) were also studied. Studies on kinetics of polymerization showed that, higher Al/Zr ratio and higher temperature lead to higher polymerization rates but lower the molecular weight. A model incorporating effect of reaction parameter on polymerization rates has been developed. | en |
