James L. Brewbaker

REINFORCEMENT OF POLYURETHANE ELASTOMERS WITH MICROFIBRES HAVING VARYING ASPECT RATIOS

A mathematical model has been used to predict the effect of fibre aspect ratio on the mechanical properties of flexible polyurethane elastomers reinforced with short, microscopic fibres. The study suggested that only a small fraction of the mechanical property improvement possible has been realized in previous attempts to reinforce polyurethane elastomers using microfibres of modest aspect ratios. It was predicted that the mechanical properties of flexible polyurethane elastomers could be improved significantly by reinforcement with small amounts of microscopic fibres having high aspect ratios. Samples were prepared and characterized to test these predictions. Good agreement was seen between the theoretically predicted property trends and those actually observed. It was observed that only 2 phr§ of microscopic bacterial cellulose fibres having high aspect ratios nearly doubled the Youngs modulus and tripled the strength of a flexible polyurethane elastomer. This reinforcement far surpassed that observed for microfibres having more modest aspect ratios.

Chain stiffness of liquid crystalline polyesters. 2. Radius of gyration and intrinsic viscosity

Abstract Continuing from the previous paper on novel liquid crystalline polymers containing the dihydroxy-α-methylstilbene (DHαMS) fragment, several conclusions were reached for random terpolymers of DHαMS terephthalate, DHαMS isophthalate and DHαMS 2,6-naphthoate; in mole fractions of 0.65, 0.10 and 0.25, respectively; by atomistic simulations and experimental work on effects of weight-average molecular weight ( M w ) on the radius of gyration ( R g ) and intrinsic viscosity [η]: I. The polydispersities of the samples are around 2.16, a typical value for condensation polymers. 2. The observed R gw , (weight-average R g ) and [η]values are both roughly proportional to M w 0.7 . 3. The calculated R g values are also ∼ M w 0.7 and comparable to the observed R gw , values. 4. The calculated [η]∼ M w 0.85 (and thus have a very similar exponent for the M w dependence), but are larger than the observed values of [η] by roughly a factor of 6 over the entire range of M w .