0000000000114238
AUTHOR
Witold Brostow
Transmission of mechanical energy through polymeric liquid crystals and their blends
Molecular composites, also called polymeric liquid crystals (PLC), are contrasted with the traditional composites; the name heterogeneous composites is proposed for the latter. Advantages of blending PLCs with ordinary engineering polymers are discussed. Results reported for blends of poly(ethylene terepthalate) (PET) with a PLC containing sequences of PET and p-hydroxybenzoic acid (PHB) include thermophysical properties, melt rheology, mechanical properties of solid blends, and scanning electron microscopy of fracture surfaces. A model called the island model was developed to explain the results: One assumes that the lines of force as well as propagating cracks tend to concentrate in the p…
Slow crack propagation in polyethylene: determination and prediction
Abstract A model is developed connecting the stress intensity factor KI with the propagation rate d h d t of slow cracks. The model is based on the concept of the chain relaxation capability. Experimental KIversus d h d t data are reported for polyethylenes of varying molecular mass M, density ϱ, initial notch length h0 and at different stress levels σ. Predictions of the theory concerning the effect of each of these parameters on crack propagation are confirmed by the experimental results. In particular, the equation for KI as a function of d h d t does not contain h0 nor σ. Experimental plots of KIversus d h d t for common M but different h0 values coincide into a single curve. Also plots…
Mechanical And Thermophysical Properties Of Polymers And Chemical Structure: From Computer Simulations To Experimental Data
Chemical structure is related to properties on the basis of results of computer modelling of mechanical behavior. An equation for the shift factor aT,c dependent on temperature T and concentration c is provided, connection to the chain relaxation capability noted, and potential application range of the approach discussed. Constituents of free volume are defined, and effects of individual constituents on mechanical properties.
Time–temperature correspondence prediction of stress relaxation of polymeric materials from a minimum of data
Abstract We have determined the stress relaxation of a longitudinal polymer liquid crystal (PLC), polypropylene and their blends containing 10 and 20% of the PLC at the constant strain of 0.5%. The results for nine temperature levels in the range between 20 and 100 °C were used to create master curves for T ref =20 ° C . The temperature shift factors aT were calculated using a general formula derived by one of us and based on free volume vf and the chain relaxation capability model. The predicted values agree with the experimental ones for all materials studied within limits of the experimental accuracy. Moreover, the relation between the shift factor aT and the reduced volume ṽ has been us…
Prediction of long-term service performance of polymeric materials from short-term tests: Creep and prediction of the stress shift factor of a longitudinal polymer liquid crystal
The material studied is a longitudinal polymer liquid crystal (PLC). The creep behavior of the PLC is examined in the region of nonlinear viscoelasticity. The creep compliance D curves at nine different stress (T levels, from 10 to 50 J.cm3 at a constant temperature are determined and shifted along the log time axis for uRf = 10 J . to produce the D versus t/a, master curve. A fairly general formula for stress shift factor a,, based on free volume vf and the chain relaxation capability (CRC) derived by one of the authors is applied. The formula predicts values that agree with the experimental ones within the limits of the experimental accuracy. Thus, experiments at several stress levels can…