Structural Parameters that Control Mechanical Properties

Structural Parameters that Control Mechanical Properties... 

Most properties of linear polymers are controlled by two different factors. The chemical constitution of the monomers determines the interaction strength between the chains, the interactions of the polymer with host molecules or with interfaces. The monomer structure also determines the possible local conformations of the polymer chain. This relationship between the molecular structure and any interaction with surrounding molecules is similar to that found for low-molecular-weight compounds. The second important parameter that controls polymer properties is the molecular weight. Contraiy to the situation for low-molecular-weight compounds, it plays a fundamental role in polymer behaviour. It determines the slow-mode dynamics and the viscosity of polymers in solutions and in the melt. These properties are of utmost importance in polymer rheology and condition their processability. The mechanical properties, solubility and miscibility of different polymers also depend on their molecular weights. 

With respect to the research in this field, all-polypropylene (PP) composites have been extensively studied. Hine et al. investigated the influence of fabrication parameters that control the hot-compaction behavior of woven-oriented PP [23,24], The results indicated that molecular weight, crystallinity, reinforcement shape and the weave style are important for controlling the composites performance. Alcock et al. created unidirectional all-PP composite laminates from co-extruded three layer tape of PP (with a copolymer homopolymer copolymer structure) via filament winding [12]. The specific mechanical properties were comparable to those reported for a commercial unidirectional glass fiber reinforced PP. 

The branching theories In their present state can treat a number of complex branching reactions of Industrial importance. It is to be stressed, however, that there does not exist any universal approach to all systems. The understanding of the reaction mechanism and kinetics is a necessary prerequisite for adaptation of the proper theory to give relations for structural parameters. Further progress in the network formation theory seems highly desirable particularly in the field of cycllzatlon and diffusion control and in understanding the network structure-properties relations. 

The process of growing a pure crystal is sensitive to a host of process parameters that impact the incorporation of impurities in the crystal, the quality of the crystal structure, and the mechanical properties of the crystal rod. For example, the crystal-pulling mechanism controls the pull rate of the crystallization, which affects the incorporation of impurities in the crystal, and the crystal rotation, which affects the crystal structure. 

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