Deformation mechanism of polystyrene toughened with sub-micrometer monodisperse rubber particles

Core-shell polybutadiene-graft-polystyrene (PB-g-PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB-g-PS blends with a constant rubber content of 20 wt%. PB-g-PS particles with a lower PB/PS ratio (<= 570/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high-impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1-3 mu m rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub-micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress-whitening zone of blends with a PB/PS ratio of 70/30 in PB-g-PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation.

Study of the blends containing core-shell latex polymer

Polycarbonate (PC) and a core-shell latex polymer composed of poly(butyl acrylate) and poly(methyl methacrylate) (PBA-cs-PMMA) as core and shell, respectively, were mixed using a Brabender-like apparatus under different conditions. The mechanical properties, the morphology and the processability of the blends were investigated. Because of the good compatibility of PC and PMMA, even dispersion of PBA-cs-PMMA in PC matrix and good adhesion between the components have been achieved. PBA-cs-PMMA is thus a very good impact modifier for PC. The toughening mechanism is both cavitation and shear yielding, as indicated by SEM observation. (C) 1997 Elsevier Science Ltd.

Vulcanization of polybutadiene latex induced by Co-60 gamma radiation

Polybutadiene latex (PBL) vulcanization induced by Co-60 radiation and the influence of dose on crosslinking were investigated. Morphology and particle size distribution were examined by AFM and a particle size analyzer. The casting films were characterized for their swelling and mechanical properties as a function of dose.

Brittle-ductile transition of particle toughened polymers: influence of the matrix properties

It was theoretically pointed out that the product of the yield stress and yield strain of matrix polymer that determined the brittle-ductile transition (BDT) of particle toughened polymers. For given particle and test condition, the higher the product of the yield stress and the yield strain of the matrix polymer, the smaller the critical interparticle distance (IDc) of the blends was. This was why the IDc (0.15 mum) of the polypropylene (PP)/rubber blends was smaller than that (0.30 mum) of the nylon 66/rubber blends, and the IDc of the nylon 66/rubber blends was smaller than that (0.60 mum) of the high density polyethylene (HDPE)/rubber blends.

The influence of core-shell structured modifiers on the toughness of poly (vinyl chloride)

The core-shell structured grafted copolymer particles of polybutadiene grafted polymethyl methacrylate (PB-g-PMMA, MB) were prepared by emulsion polymerization. The MB particles were used to modify poly (vinyl chloride) (PVC) by melt blending. The mechanical properties of the PVC blends were investigated. The micro-morphology of the PVC blends was observed by scanning electron microscopy (SEM). The results indicated that the samples with the best impact strength could be obtained when the core-shell weight ratio of PB to PMMA is lower than 93:7, the mechanical properties correlated well with SEM morphologies, the addition of modifier with the ratio core to shell of 93:7 could reduce the domain size of the dispersed phase. Furthermore, the compatibility and properties of the blends were greatly enhanced and improved. The modifier particles could be well dispersed in the PVC matrix.

Dynamic mechanical studies of the sulfonated butyl rubber ionomers and their blends

Dynamic mechanical properties of sulfonated butyl rubber ionomers neutralized with different amine or metallic ion (zinc or barium) and their blends with polypropylene (PP), high-density polyethylene (HDPE), or styrene-butadiene-styrene (SBS) triblock copolymer were studied using viscoelastometry. The results showed that glass transition temperatures of ion pair-containing matrix and ionic domains (T-g1 and T-g2, respectively) of amine-neutralized ionomers were lower than those of ionomers neutralized with metallic ions, and the temperature range of the rubbery plateau on the storage modulus plot for amine-neutralized ionomers was narrower. The modulus of the rubbery plateau for amine-neutralized ionomers was lower than that of ionomers neutralized with zinc or barium ion. With increasing size of the amine, the temperature range for the rubbery plateau decreased, and the height of the loss peak at higher temperature increased. Dynamic mechanical properties of blends of the zinc ionomer with PP or HDPE showed that, with decreasing ionomer content, the T-m of PP or HDPE increased and T-g1 decreased, whereas T-g2 or the upper loss peak temperature changed only slightly. The T-g1 for the blend with SBS also decreased with decreasing ionomer content. The decrease of T-g1 is attributed to the enhanced compatibilization of the matrix of the ionomer-containing ion pairs with amorphous regions of PP or HDPE or the continuous phase of SBS due to the formation of thermoplastic interpenetrating polymer networks by ionic domains and crystalline or glassy domains.

Effects of rubber content and temperature on unstable fracture behavior in ABS materials with different particle sizes

The fracture behavior of ABS materials with a particle diameter of 110 nm and of 330 nm was studied using instrumented Charpy impact tests. The effects of rubber content and temperature on fracture behavior, deformation mode, stable crack extension, plastic zone size, J-integral value, and crack opening displacement were investigated. In the case of a particle size of 110 nm, the material was found to break in a brittle manner, and the dominant crack mechanism was unstable crack propagation. Fracture toughness increases with increasing rubber content. In the case of a particle size of 330 nm, brittle-to-tough transition was observed. The J-integral value first increases with rubber content, then levels off after the rubber content is greater than 16 wt %. The J-integral value of a particle diameter of 330 nm was found to be much greater than that of 110 nm. The J-integral value of both series first increased with increasing temperature until reaching the maximum value, after which it decreased with further increasing temperature. The conclusion is that a particle diameter of 330 nm is more efficient than that of 110 nm in toughening, but for both series the effectiveness of rubber modification decreases with increasing temperatures higher than 40 degreesC because of intrinsic craze formation in the SAN matrix at temperatures near the glass transition of SAN. (C) 2000 John Wiley & Sons, Inc.

Toughening of nylon with epoxidised ethylene propylene diene rubber

Blends of nylon-6 and epoxidised ethylene propylene diene (eEPDM) rubber were prepared through reactive mixing. It is found that the toughness of nylon-6 can be much improved by this method, and that the particle size of eEPDM is much smaller than that of unexpoxidised EPDM (uEPDM) rubber in a nylon-6 matrix. This indicates that the epoxy group in eEPDM could react with a nylon-6 end group to form a graft copolymer which could act as an interfacial compatibiliser between the nylon-6 and the eEPDM rubber dispersed phase. (C) 1998 Elsevier Science Ltd. All rights reserved.

Toughened blend of polycarbonate and epoxidized ethylene propylene diene rubber

A super-tough polycarbonate (PC) blend was obtained by using epoxidized ethylene propylene diene (eEPDM) rubber as modifier. The notched Izod impact strength of PC/eEPDM (96/4) blend shows a great improvement, with a value about 25 times of that of pure PC. Finely and homogeneously dispersed rubber particles (0.2-0.8 mu m) in the PC matrix indicated good adhesion between the eEPDM rubber phase and the PC matrix. (C) 1997 Elsevier Science Ltd.

Toughening of poly(butylene terephthalate) with epoxidized ethylene propylene diene rubber

In this paper, unepoxidized ethylene propylene diene rubber (uEPDM) was first epoxidized with formic acid and H2O2, and then the epoxidized ethylene propylene diene rubber (eEPDM) was melt-mixed with PET resin in a Brabender-like apparatus. Toughening of PET matrix was achieved by this method. The dispersion of rubber particles and phase structure of the blends were also observed by SEM. It has been suggested that the epoxy groups in the eEPDM could react with PET end groups to form a graft copolymer which could act as an interfacial compatibilizer between the PBT matrix and eEPDM rubber dispersed phase. This is beneficial to the improvement of the impact performance of PBT. (C) 1997 Elsevier Science Ltd.

Toughened poly(butylene terephthalate) by epoxided ethylene-propylene-diene-rubber

Blends of poly (butylene terephthalate) (PBT) and epoxided ethylene-propylene-diene terpolymer (EEPDM) were prepared. Their mechanical properties and morphology were studied by Izod impact test machine and scanning electronic microscope respectively, It was found that the notched Izod impact strength of blend PBT/EEPDM was as about 23 times as that of pure PET and about 10 times as that of blend PBT/EPDM at room temperature, The dispersed rubber particles were much smaller and the phase boundary was more blurred in blend PBT/EEPDM than in blend PBT/EPDM. The toughness of blend PBT/EEPDM was much more better than that of blend PET and PBT/EPDM, which was in good agreement with the difference between their morphologies.

Size-dependent inelastic behavior of particle-reinforced metal-matrix composites

The strengthening behavior of particle-reinforced metal-matrix composites (MMCp) is primarily attributed to the dislocation strengthening effect and the load-transfer effect. To account for these two effects in a unified way, a new hybrid approach is developed in this paper by incorporating the geometrically necessary dislocation strengthening effect into the incremental micromechanical scheme. By making use of this hybrid approach, the particle-size-dependent inelastic deformation behavior of MMCp is given. Some comparisons with the available experimental results demonstrate that the present approach is satisfactory.

An Amino Acid Substitution Matrix for Protein Conformation Identification

Amino acid substitution matrices play an essential role in protein sequence alignment, a fundamental task in bioinformatics. Most widely used matrices, such as PAM matrices derived from homologous sequences and BLOSUM matrices derived from aligned segments of PROSITE, did not integrate conformation information in their construction. There are a few structure-based matrices, which are derived from limited data of structure alignment. Using databases PDB_SELECT and DSSP, we create a database of sequence-conformation blocks which explicitly represent sequence-structure relationship. Members in a block are identical in conformation and are highly similar in sequence. From this block database, we derive a conformation-specific amino acid substitution matrix CBSM60. The matrix shows an improved performance in conformational segment search and homolog detection.

Flow Stress of Biomorphous Metal-Matrix Composites

For metal-matrix composites (MMCs), interfacial debonding between the ductile matrix and the reinforcing hard inclusions is an important failure mode. A fundamental approach to improving the properties of MMCs is to optimize their microstructure to achieve maximum strength and toughness. Here, we investigate the flow stress of a MMC with a nanoscale microstructure similar to that of bone. Such a 'biomorphous' MMC would be made of staggered hard and slender nanoparticles embedded in a ductile matrix. We show that the large aspect ratio and the nanometer size of inclusions in the biomorphous MMC lead to significantly improved properties with increased tolerance of interfacial damage. In this case, the partially debonded inclusions continue to carry mechanical load transferred via longitudinal shearing of the matrix material between neighboring inclusions. The larger the inclusion aspect ratio, the larger is the flow stress and work hardening rate for the composite. Increasing the volume concentration of inclusion also makes the biomorphous MMC more tolerant of interfacial damage.