Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends. Correlation between Poisson ratio and adhesion

The deformation behavior of blends contg. polystyrene (I) [9003-53-6], low-d. polyethylene (II) [9002-88-4], and a hydrogenated butadiene-styrene diblock copolymer (III) was examd. by tensile testing with simultaneous vol. measurements. Assuming that shearing causes no vol. changes, crazing, after yielding, was the only deformation mechanism in blends with low I and III contents. Shearing became important in blends with high I concns. due to formation of a semicontinuous low modulus phase. The decrease in the Poisson ratio with increasing II content in I-II blends, as opposed to an increase in the presence of III, shows the Poisson ratio to be very sensitive to adhesion between the components. The toughness of I-II blends is discussed in terms of concns. of craze nuclei. Too few craze nuclei give rise to brittle failure because the resulting low no. of crazes cannot accommodate much deformation of the matrix whereas too many craze nuclei also cause brittle failure because of the high probability of combination of the crazes to form a crack. The concn. of craze nuclei depends on the no. of dispersed particles and their adhesion to the matrix. [on SciFinder (R)

The constant stress behavior of polystyrene-low density polyethylene blends

The constant-stress behaviour of low-density polyethylene toughened polystyrene has been analysed. It was found that the initial strain-time behaviour during constant-stress tensile tests is well described by a simple model that predicts a proportionality between strain and the square of time, provided a correction for craze formation during the application of stress is made. By analysing strain-time curves at different stresses it has been determined that the product of the rates of craze initiation and of craze growth is exponentially dependent on stress. The attainment of a constant strain rate during constant-stress experiments and the attainment of a constant-stress level during constant strain-rate experiments result from a strong decrease in the rate of craze initiation. This effect allowed the determination of the stress and temperature dependences of the rate of craze growth. This rate was found to be well described by the Eyring equation, which is in agreement with earlier results obtained from constant stress- and strain-rate experiments

A model for the stress-strain behavior of toughened polystyrene. Part 1

A model was developed to detn. the rates of craze initiation and craze growth in opaque materials that deform by crazing, such as toughened polystyrene [9003-53-6], and to predict their stress-strain behavior. Crazed polystyrene toughened with low-d. polyethylene [9002-88-4] can be regarded as a series of linearly elastic crazes and toughened polystyrene. This implies that the amt. of craze material, stress, and strain are related in a simple fashion. As the amt. of craze material can be calcd. from the rates of craze initiation and craze growth, stress-time behavior can be calcd. if strain-time behavior is known, and vice vers

Modeling stress-strain behavior of polyethylene-toughened polystyrene

A stress-strain relation was derived for polymers that deform by crazing, and good agreement was obtained with exptl. values. By analyzing const. strain and stress rate expts., the relation can be used to det. the stress dependence of the rates of craze initiation and craze growth. The results from these analyses were applied to solve the relation for const. stress and strain rate expt

Morphology and mechanical interaction at polymer-polymer interface in block copolymer modified blends

A review with 8 refs. on morphol. and mech. properties of polystyrene (I) [9003-53-6] blends with low-d. polyethylene (II) [9002-88-4] contg. block ethylene-styrene copolymer [25068-12-6] at the I-II interface

A mathematical relation between volume strain, elongational strain and stress in homogeneous deformation

A model is presented for the vol. strain of a two-phase blend which elongates homogeneously in a tensile test app. In the case when only elastic deformation and crazing take place, the vol. strain vs. elongation curve can be constructed and calcd. from the data of the stress-strain curve alone. When, as well as crazing and elastic deformation, shearing takes place, the data of the stress vs. elongation curve and the vol. strain vs. elongation curve can be used to calc. the sep. contributions of the three deformation mechanisms at any elongation. In principle, the model can be also used for any homogeneous system which deforms without necking and where one or more deformation mechanism is present. [on SciFinder (R)

Strain-rate dependence of the yield stress of toughened polystyrene

A simplified version of the authors' earlier equation (1982) predicts the stress-strain behavior of toughened polystyrene [9003-53-6] with reasonable accuracy. The sum of the activation enthalpies of craze initiation and growth was calcd. to be 144 kJ/mol, compared to 149 kJ/mol calcd. using the nonsimplified stress-strain equatio