Polystyrene Low-density Polyethylene Research Articles

Discrimination of adhesion and viscoelasticity from nanoscale maps of polymer surfaces using bimodal atomic force microscopy.

The simultaneous excitation and measurement of two eigenmodes in bimodal atomic force microscopy (AFM) during sub-micron scale surface imaging augments the number of observables at each pixel of the image compared to the normal tapping mode. However, a comprehensive connection between the bimodal AFM observables and the surface adhesive and viscoelastic properties of polymer samples remains elusive. To address this gap, we first propose an algorithm that systematically accommodates surface forces and linearly viscoelastic three-dimensional deformation computed via Attard's model into the bimodal AFM framework. The proposed algorithm simultaneously satisfies the amplitude reduction formulas for both resonant eigenmodes and enables the rigorous prediction and interpretation of bimodal AFM observables with a first-principles approach. We used the proposed algorithm to predict the dependence of bimodal AFM observables on local adhesion and standard linear solid (SLS) constitutive parameters as well as operating conditions. Secondly, we present an inverse method to quantitatively predict the local adhesion and SLS viscoelastic parameters from bimodal AFM data acquired on a heterogeneous sample. We demonstrate the method experimentally using bimodal AFM on polystyrene-low density polyethylene (PS-LDPE) polymer blend. This inverse method enables the quantitative discrimination of adhesion and viscoelastic properties from bimodal AFM maps of such samples and opens the door for advanced computational interaction models to be used to quantify local nanomechanical properties of adhesive, viscoelastic materials using bimodal AFM.

The effect of the architecture and concentration of styrene–butadiene compatibilizers on the morphology of polystyrene/low‐density polyethylene blends

AbstractThe effect of styrene–butadiene block copolymers (SB) with varying number of blocks and length of styrene blocks on the morphology, rheology, and impact strength of 4/1 polystyrene/low‐density polyethylene (PS/LDPE) blends was studied. The scanning and transmission electron microscopy and X‐ray scattering were used for determination of the size of LDPE particles and the localization and structure of SB copolymers in blends. It is shown that the dependence of the LDPE particle size on the amount of added SB and localization of SB copolymers in blends is predominantly controlled by the length of their styrene blocks. It follows from thermodynamic considerations that the reason is the difference in composition asymmetry between SB with short and long styrene blocks. Coalescence of particles of SB having short styrene blocks at the surface of LDPE droplets and movement of SB with long styrene blocks to the PS–LDPE interface were observed during annealing of PS/LDPE/SB blends. Pronounced migration of SB copolymer during annealing shows that their localizations in blends in steady state on long steady mixing and at thermodynamic equilibrium are different. The values of tensile impact strength of PS/LDPE/SB blends correlate well with the size of LDPE particles and the amount of SB at the interface. Viscosity of PS/LDPE/SB depends on molecular structure of SB copolymers by a manner different from that of tensile impact strength. The results of this study and literature data lead to the conclusion that the compatibilization efficiency of SB copolymers for a certain polystyrene‐polyolefin pair is a function of not only molecular parameters of SB but also of the polystyrene/polyolefin ratio, the amount of SB in a blend, and mixing and processing conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2803–2816, 2006

Morphology and deformation of compatibilized polystyrene low density polyethylene blends

This investigation deals with the morphology and tensile behavior of polystyrene/low density polyethylene blends compatibilized by hydrogenated styrene-b-butadiene-b-styrene triblock copoly- mer. The stress-strain measurements indicate that blends with excellent toughness were achieved, due to the compatibilizing role of the triblock copolymer in the system. The morphology of the blends was observed by scanning electron microscopy (SEM), and the results show that the state of polystyrene changes from continuous phase to dispersed phase with increasing LDPE content. The correlation between mechanical properties and morphology is discussed. The morphologies of the tensile bars were also examined by SEM, and the deformation mechanisms of the blend were further analysed according to fractography. # 1999 Society of Chemical Industry

The effect of interfacial interactions on the rheo-optical behaviour of compatibilized polystyrene/low-density polyethylene/styrene-ethylene-butylene-styrene copolymer blends

The influence of styrene-ethylene-butylene-styrene (SEBS) triblock copolymers on the interfacial interactions in heterogeneous polystyrene/low-density polyethylene (PS/LDPE) blends was studied by simultaneous Fourier transform infra-red (FTi.r.) spectroscopic and stress-strain (rheo-optical) measurements. Values of the dichroic ratio (DR) for a specific absorption band of the dispersed LDPE phase were determined from the polarized spectra as a function of extension (λ), and were taken as a measure of the molecular orientation of the LDPE. A linear relationship between DR and ln λ was found, and the slope was interpreted as a reflection of the interfacial interactions in the heterogeneous blends. The slope increased with the amount of a low-molecular-mass SEBS which was added, but was less affected by the addition of a high-molecular-mass SEBS. The difference was explained by a lower concentration of the high-molecular-mass copolymer at the interphase.

Influence of electron beam irradiation on the microrheology of incompatible polymer blends: Thread break‐up and coalescence

The microrheology of polymer blends as influenced by crosslinks induced in the dispersed phase via electron beam irradiation, is systematically investigated for the model system polystyrene/low density polyethylene (PS/LDPE). Both break‐up of threads and coalescence of particles are delayed to a large extent, but are not inhibited completely and occur faster than would be expected for a nonirradiated material with a comparable viscosity. Small amplitude, dynamic rheological measurements indicated that in the irradiated materials a yield stress could exist. In contrast, direct microrheological measurements showed that this yield stress, which would prevent both break‐up and coalescence, could not be realized by EB irradiation. Apparently, the direct study of the microrheology of a blend system is important for the prediction of the development of its morphology and it is not possible to rely only on rheological data obtained via other methods.

The constant stress behaviour 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.