THE PREPARATION AND CHARACTERIZATION OF SBR／PS CORE-SHELL PARTICLES BY GAMMA IRRADIATION

A kind of core(SBR)-shell(PS) particles was synthesized by using SBR latex and grafting with St under gamma irradiation. The influences of absorbed dose and dose rate on the grafting yield of PS on SBR seed latex have been investigated. Results show there was a transition layer which contained the SBR/PS graft copolymer between the SBR core and PS shell. Dynamic laser scattering (DLS) and differential scanning calorimetry (DSC) results confirm the existence of grafted polystyrene, and transmission electron microscope (TEM) observation verifies the core-shell structure of SBR-g-PS latex. Such SBR/PS core-shell latex could be processed easily to ultrafine rubber powders by using spray drying and expected to be used as an impact modifier for PS.     

Positron annihilation study of high impact polystyrene

Positron lifetime spectra for general purpose polystyrene (GPPS), polybutadiene rubber (PBR), and their copolymers, styrenebutadiene rubber (SBR) and high impact polystyrene (HIPS) have been measured. It has been found that the free volumes in the copolymers are smaller than the average over the individual polymers, due to the interfacial interaction between the styrene and rubber phases. A long-lived component with a mean lifetime of about 123 ns was observed in the spectrum for deformed HIPS, showing the existence of ortho-positronium (o-Ps) in the deformation induced crazes.     

Impact modification of thermoplastics by methyl methacrylate and styrene-grafted natural rubber latexes

The preparation and characterization of polymer blends with structured natural rubber (NR)-based latex particles are presented. By a semicontinuous emulsion polymerization process, a natural rubber latex (prevulcanized or not) was coated with a shell of crosslinked polymethylmethacrylate (PMMA) or polystyrene (PS). Furthermore, core–shell latexes based on a natural rubber/crosslinked PS latex semi-interpenetrating network were synthesized in a batch process. These structured particles were incorporated as impact modifiers into a brittle polymer matrix using a Werner & Pfleiderer twin screw extruder. The mechanical properties of PS and PMMA blends with a series of the prepared latexes were investigated. In the case of PMMA blends, relatively simple core (NR)–shell (crosslinked PMMA) particles improved the mechanical properties of PMMA most effectively. An intermediate PS layer between the core and the shell or a natural rubber core with PS subinclusions allowed the E-modulus to be adjusted. The situation was different with the PS blends. Only core–shell particles based on NR-crosslinked PS latex semi-interpenetrating networks could effectively toughen PS. It appears that microdomains in the rubber phase allowed a modification of the crazing behavior. These inclusions were observed inside the NR particles by transmission electron microscopy. Transmission electron photomicrographs of PS and PMMA blends also revealed intact and well-dispersed particles. Scanning electron microscopy of fracture surfaces allowed us to distinguish PS blends reinforced with latex semi-interpenetrating network-based particles from blends with all other types of particles.     

Structured latex particles as impact modifiers for poly(styrene–co-acrylonitrile) blends

This work was focused on the influence of the morphology of composite natural rubber (NR)-based particles on the toughness of poly(styrene–co-acrylonitrile) (PSAN) blends. In order to be suitable for the reinforcement of PSAN blends, the NR-based particles were coated with a shell of crosslinked poly(methylmethacrylate) (PMMA). Furthermore, polystyrene (PS) subinclusions were introduced into the NR rubber core. PSAN blends were prepared by adding the wet latex directly into a twin screw-extruder. This new method allowed even tacky pure rubber particles to be dispersed as shown by transmission electron photomicrographs which confirmed the integrity of the soft particles after mixing. Solid NR particles or NR-based latex particles containing rigid PS subinclusions and no hard shell did not offer any impact improvement to PSAN. Only NR-based core–shell particles containing at least 25% PMMA in the shell toughened the brittle matrix. Prevulcanized NR-based latex particles which do not cavitate easily were less effective. Core–shell particles containing PS subinclusions within a natural rubber core allowed more effective use of the rubber phase. From the fracture surface morphology the failure mechanisms of PSAN blends containing the different composite NR particles could be deduced. Monodisperse poly(n-butylacrylate)-based core–shell particles were too small to toughen PSAN. However, a similar dependence of the fracture mechanisms on the morphology of the incorporated toughening agent could be established by scanning electron microscopy.     

Influence of the structural characteristic of pyrolysis products on thermal stability of styrene-butadiene rubber composites reinforced by different particle sized kaolinites

A series of rubber composites were prepared by blending styrene-butadiene rubber (SBR) latex and the different particle sized kaolinites. The thermal stabilities of the rubber composites were characterized using thermogravimetry, digital photography, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Kaolinite SBR composites showed much greater thermal stability when compared with that of the pure SBR. With the increase of kaolinite particle size, the pyrolysis products became much looser; the char layer and crystalline carbon content gradually decreased in the pyrolysis residues. The pyrolysis residues of the SBR composites filled with the different particle sized kaolinites showed some remarkable changes in structural characteristics. The increase of kaolinite particle size was not beneficial to form the compact and stable crystalline carbon in the pyrolysis process, and resulted in a negative influence in improving the thermal stability of kaolinite/SBR composites.     

Ion-Free latex films as dual-phase electrolytes: Styrene–butadiene rubber and nitrile–butadiene rubber synthesized by emulsion polymerization with poly-(vinyl pyrrolidone) stabilizer

Ion-free latices of styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR) were synthesized by emulsion polymerization with use of poly (vinyl pyrrolidone) (PVP) stabilizer. The goal was to prepare ion-free latex films, possessing dual-phase latex particle morphology, and swell the films with liquid electrolyte to yield dual-phase polymer electrolytes (DPE). SBR/PVP latex was prepared readily, but NBR/PVP latex was sensitive to coagulation. Differential scanning calorimetric (DSC) and scanning electron microscopic (SEM) analyses of latex films provided morphological evidence concerning particle structure and phase separation. Blends of NBR/PVP and PB/PVP latices (PB = polybutadiene) were also investigated, but particle structure was not present in the blended latex film, even though particle structure was present in the individual NBR/PVP and PB/PVP latex films. After extensive swelling of SBR/PVP latex films, PVP was extracted from the films, and ionic conductivities greater than 10^?3 S/cm were achieved. © 1994-John Wiley & Sons, Inc.     

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex

The sensitizing effect of acrylates on radiation vulcanization of natural rubber latex was studied. The results indicate that Gc value of crosslinking (Gc) will be higher at the same radiation dose when a sensitizer exists, and Gc value decreases with the increase of radiation dose (D) conforming to the formula Gc=KD^-α, where K and α are constants depending on sensitizers. The more sensitizers added, the greater the Gc value. However, the viscosity of the natural rubber latex also increases rapidly along with the increase of sensitizers added.Some sensitizers, such as TMPTA, can decrease the optimum dose from about 200 kGy to approximately 20 kGy according to our experiment. The tensile strength of the film can reach round 20 MPa. Other physical properties are comparable to those of unsensitized.     

Poly(2-acetoxyethyl methacrylate)/polystyrene latex interpenetrating polymer networks with well-defined phase-separated structure

A series of poly(2-acetoxyethyl methacrylate)/polystyrene(PAEMA/PS) latex interpenetrating polymer networks(LIPNs) were prepared by seeded soap-free emulsion polymerization of styrene on the crosslinked PAEMA seed particles using an oil-soluble initiator.These PAEMA/PS LIPNs showed a well-defined phase-separated structure with PS phase dispersing in continuous PAEMA phase.The domain size of PS phase was found to depend on the crosslinking degree of PAEMA seed particles and the amount of second-stage styrene monomer.     

Morphology,structure, and properties of in situ compatibilized linear low‐density polyethylene/polystyrene and linear low‐density polyethylene/high‐impact polystyrene blends

Blends of linear low‐density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high‐impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl₃), was adopted to initiate the Friedel–Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl₃ blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel–Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE‐g‐PS and LLDPE‐g‐HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m². Scanning electron microscopy micrographs showed that the size of the domains decreased from 4–5 to less than 1 μm, depending on the content of added AlCl₃. The crystallization behavior of the LLDPE/PS blend was investigated with differential scanning calorimetry. Fractionated crystallization phenomena were noticed because of the reduction in the size of the LLDPE droplets. The melt‐flow rate of the blending system depended on the competition of the grafting reaction of LLDPE with PS and the degradation of the blending components. The degradation of PS only happened during the alkylation reaction between LLDPE and PS. Gel permeation chromatography showed that the alkylation reaction increased the molecular weight of the blend polymer. The low molecular weight part disappeared with reactive blending. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1837–1849, 2003     

Physicochemical Characteristics of Styrene-Butadiene Latex- modified Mortar Composite vis-à-vis Preferential Interactions

The interaction between styrene-butadiene rubber (SBR) film and the ions from C₂S and C₃S hydration of Portland cement mortar composites has been evaluated by Fourier Transform Infrared Spectroscopy (FTIR), and the morphology of the composites characterized with scanning electron microscopy (SEM). The specimen used was cured for 28 days. FTIR spectrum supports the interaction of SBR with cement in the composite. Compressive strength, bulk density and water absorption properties of the cured composites were tested. Addition of SBR latex in Portland cement mortar increases the compressive strength and decreases the water absorption. Bulk density study revels interface formation in the composite. The role of the interface in relation to compressive strength of the composite has been discussed. A simple Matrix System model is shown to account composition dependence of bulk density.     

Changes in the microstructure and morphology of high-impact polystyrene subjected to multiple processing and thermo-oxidative degradation

Multiple processing and thermo-oxidation have been employed to simulate the degradative processes to which high-impact polystyrene (HIPS) is subjected during processing, service life, and mechanical recycling. A curve-fitting procedure has been proposed for the analysis of the individual bands corresponding to polybutadiene microstructure resulting from Raman spectroscopy. The analysis of the glass transition relaxations associated with the polybutadiene (PB) and polystyrene (PS) phases has been performed according to the free-volume theory. Both reprocessing and thermo-oxidative degradation are responsible for complex physical and chemical effects on the microstructure and morphology of PB and polystyrene PS phases, which ultimately affect the macroscopic performance of HIPS. Multiple processing affects PB microstructure and the free-volume parameter associated with the PS phase. Physical ageing of the PS phase predominates for shorter exposure to thermo-oxidation; after prolonged exposure, however, the chemical effects on the PB phase become significant and strongly influence the overall structure.     

Modification of Rubber by Cardanol-Formaldehyde Resins and Epoxidized Cardanol

Abstract

Cardanol-formaldehyde resin (CF) and cardanol glycidylether (CGE) have been synthesized for reinforcing natural rubber (NR), a blend of NR and styrene-butadiene rubber (SBR), and nitrile-butadiene rubber (NBR). The novolac CF resin reinforced the NR, SBR, and NBR. The resolic CF is not only a reinforcing agent but also a hardener (crosslinking agent) for NBR by means of the methylol groups of CF with the CN- group of NBR. The CGE resin was synthesized by the epoxidation of cardanol by epichlorohydrin; it could be used as a reinforcing agent for NR and for crosslinking maleinized NR. The results of estimates of the physical properties of the vulcanisate, their DSC diagrams, and SEM showed the enhanced properties of the final products.     

高抗冲聚苯乙烯中银纹的引发与终止

银纹是由孔穴和断裂面间相联结的原纤维组成的微小裂纹,其中原纤维的体积分数可达40%.银纹的体积分数与材料的韧性成正比.银纹化是高抗冲聚苯乙烯(ＨＩＰＳ)在脆化温度以下,抵抗破坏而消耗外界能量的主要方式.银纹的产生与材料内部不均一性所导致的应力集中有关.ＨＩＰＳ中的橡胶粒子能够控制银纹在本体中均匀地发展,这是ＨＩＰＳ高韧性的原因[1].ＨＩＰＳ的分散相是由聚丁二烯(ＰＢ)为连续相,ＰＳ为分散相构成的细胞结构粒子.通常ＨＩＰＳ中ＰＢ的含量为7%～8%,而细胞结构粒子的体积分数可高达23%,可见细胞结构粒子内部ＰＳ的含量为ＰＢ的…     

Studies on the rubber phase stability in gamma irradiated polystyrene-SBR blends by using FT-IR and Raman spectroscopy

Improvement in the impact properties of polystyrene-SBR blends produced by different concentrations and types of styrene-butadiene rubber (SBR) was studied. The samples were gamma irradiated at different doses to achieve good adhesion, and consequently good stability, between the rubbery phase and the polystyrene matrix, producing an improvement in the impact properties. The results show that the best Izod impact was obtained for a blend with 10% SBR and with a dose of 100 kGy. Several samples with 0%, 3%, 5% and 10% of SBR were prepared and characterized by FT-IR and FT-Raman spectroscopies.     

Exfoliated high-impact polystyrene/MMT nanocomposites prepared using anchored cationic radical initiator-MMT hybrid

High-impact polystyrene (HIPS)/montmorillonite (MMT) nanocomposites were prepared via in-situ polymerization of styrene in the presence of polybutadiene, using intercalated cationic radical initiator-MMT hybrid. Incomplete exfoliation of the silicate layers in the HIPS nanocomposites was observed when a bulk polymerization was employed. On the other hand, the silicate layers were efficiently exfoliated in the PS matrix during a solution polymerization, due to the low extra-gallery viscosity, which can facilitate the diffusion of styrene monomers into the clay layers. The resulting exfoliated HIPS/MMT nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, particle size analysis, gel permeation chromatography, and dynamic mechanical analysis. The nanocomposites exhibited significant improvement in thermal and mechanical properties. For example, about 50% improvement in Young’s modulus was achieved with 5 wt% of clay, compared to the unmodified polymer counterpart.     

Modification of aqueous polyurethanes by forming latex interpenetrating polymer networks with polystyrene

A series of latex particles with interpenetrating polymer network structure have been synthesized from waterborne polyurethane (PU) and polystyrene (PS). The effect of PU/PS composition, cross-linking density in the PS domain as well as in PU have been studied in terms of dispersion size, transmission electron microscopy morphology, mechanical and dynamic mechanical properties in addition to swellability in water and toluene of the dispersion cast film. It was found that inverted core (PS)–shell (PU) morphology was well defined and that the domain size as well as the film properties were well controlled by the latex composition and cross-linking density of both phases. Received: 15 March 2000 Accepted: 21 February 2001     

Morphology and grafting reactions in core/shell latexes

The particle morphology and percent grafting were investigated as a function of the crosslink density of the seed latex in two systems of core/shell latexes of polybutadiene/polymethyl methacrylate (PB/PMMA) and styrene–butadiene rubber/polymethyl methacrylate (SBR/PMMA) prepared by seeded emulsion polymerization at 50°C. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to characterize the grafting efficiency of the core/shell latexes. The percent grafting of the shell polymer was found to decrease with increasing the crosslink density of the core material. The particle morphology and precent grafting were also investigated as a function of composition and structure of the core material in four core/shell latex systems: polybutadiene/styrene–acrylonitrile copolymer (PB/SAN), (styrene-butadiene) random copolymer/styrene acrylonitrile copolymer (S:B/SAN), polystyrene : polybutadiene/styrene-acrylonitrile copolymer (PS:PB/SAN) and Kraton/styrene-acrylonitrile copolymer (Kraton/SAN), which were prepared by direct emulsification for the seed followed by emulsion polymerization at 70°C for the shell polymer. Grafting and crosslinking of the core material were found to be competitive reactions depending on the microstructure of the seed latex.     

Morphology and mechanical and viscoelastic properties of natural rubber and styrene butadiene rubber latex blends

The morphology and mechanical and viscoelastic properties of a series of blends of natural rubber (NR) and styrene butadiene rubber (SBR) latex blends were studied in the uncrosslinked and crosslinked state. The morphology of the NR/SBR blends was analyzed using a scanning electron microscope. The morphology of the blends indicated a two phase structure in which SBR is dispersed as domains in the continuous NR matrix when its content is less than 50%. A cocontinuous morphology was obtained at a 50/50 NR/SBR ratio and phase inversion was seen beyond 50% SBR when NR formed the dispersed phase. The mechanical properties of the blends were studied with special reference to the effect of the blend ratio, surface active agents, vulcanizing system, and time for prevulcanization. As the NR content and time of prevulcanization increased, the mechanical properties such as the tensile strength, modulus, elongation at break, and hardness increased. This was due to the increased degree of crosslinking that leads to the strengthening of the 3‐dimensional network. In most cases the tear strength values increased as the prevulcanization time increased. The mechanical data were compared with theoretical predictions. The effects of the blend ratio and prevulcanization on the dynamic mechanical properties of the blends were investigated at different temperatures and frequencies. All the blends showed two distinct glass‐transition temperatures, indicating that the system is immiscible. It was also found that the glass‐transition temperatures of vulcanized blends are higher than those of unvulcanized blends. The time–temperature superposition and Cole–Cole analysis were made to understand the phase behavior of the blends. The tensile and tear fracture surfaces were examined by a scanning electron microscope to gain an insight into the failure mechanism. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2189–2211, 2000     

Radiation effects on the immiscible polymer blend of nylon1010 and high-impact strength polystyrene (II): mechanical properties and morphology

The paper studies the morphology and mechanical properties of immiscible binary blends of the nylon 1010 and HIPS through the radiation crosslinking method. In this blend, the HIPS particles were the dispersed phases in the nylon1010 matrix. With increasing of dose, the elastic modulus increased. However, the tensile strength, elongation at break and the energy of fracture increased to a maximum at a dose of 0.34 MGy, then reduced with the increasing of dose. SEM photographs show that the hole sizes are not changed obviously at low dose and at high dose, remnants that cannot be dissolved in formic acid and THF can be observed in the holes and on the surface. TEM photographs showed that radiation destroys the rubber phases in the polymer blend.     

Effects of vulcanization accelerator functionalized graphene on the co-vulcanization kinetics and mechanical strength of NR/SBR blends

Rubber blends are widely used for combining the advantages of individual rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process are still a challenge. Herein, high resolution pyrolysis gas chromatography-mass spectrometry (PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene-butadiene rubber (SBR) in their blends filled with graphene. It is shown that the crosslinking rate of NR chains (k_NR) was much lower than that of SBR chains (k_SBR) in the unfilled blends and blends with untreated graphene. Interestingly, the gap between k_SBR and k_NR was narrowed effectively in the blends with vulcanization accelerator grafted graphene, showing a better co-vulcanization of NR and SBR. In addition, the vulcanization accelerator grafted graphene was uniformly dispersed in rubber matrix and endowed rubber blends with higher mechanical strength and thermal conductivity did the untreated graphene.