No abstract

No abstract

No abstract

A linear low-density polyethylene (LLDPE) matrix was modified with an organic peroxide and by a reaction with maleic anhydride (MAn) and was simultaneously compounded with untreated wood flour in a twinscrew extruder. The thermal and mechanical properties of the modified LLDPE and the resulting composites were evaluated. The degree of crystallinity was reduced in the modified LLDPE, but it increased with the addition of wood flour for the formation of the composites. Significant improvements in the tensile strength, ductility, and creep resistance were obtained for the MAn-modified composites. This enhancement in the mechanical behavior could be attributed to an improvement in the compatibility between the filler and the matrix.

No abstract

No abstract

Viscoelastic properties of model poly(dimethylsiloxane) networks with pendant chains composed of linear molecules of known and uniform molecular weights are studied. It was found that the loss modulus (G‘‘) of these networks depends on the concentration and the molecular weight of the dangling chains. The dependency of the relaxation times of pendant chains on their molecular weights, proposed by de Gennes, was verified using the values of G‘‘ measured experimentally. Elastic properties of these networks decrease due to the presence of the pendant chains. This results in a reduction in the amount of elastically active chains. Low-frequency elastic moduli of the networks are coincident with equilibrium values predicted by the theory of rubber elasticity, provided that the contribution of trapped entanglements is taken into account. Values of elastic moduli obtained from swelling experiments also show excellent agreement with theoretical values.

A recursive approach is used to evaluate the resulting molecular structure of a networkforming system composed of a mixture of bifunctional and monofunctional prepolymer chains reacting with a polyfunctional cross-linker (Af + B2 + B1). This system can be used to find formulations for model networks with pendant chains composed of linear molecules of known and uniform molecular weight. Several important molecular parameters, such as the weight fraction of pendant chains, number-and weight-average molecular weights, and polydispersity of the pendant chains in the network, are calculated as a function of the weight fraction of monofunctional chains (B1) added to the reaction mixture. In a naive analysis of the system Af + B2 + B1, it may be wrongly assumed that networks obtained from the reaction of these components are formed by elastically active chains comprising B2 molecules and pendant chains comprising B1 molecules. A careful analysis shows that this hypothetical situation would take place only under certain formulation conditions. Either a defect or an excess of cross-linker leads to networks with branched pendant structures. Calculations also show that, even for stoichiometrically balanced, completely reacted networks, there exists a limiting amount of monofunctional chains that can be added to the reaction mixture to obtain model networks with linear pendant chains.