Microstructure and mechanical properties of ternary phase polypropylene/elastomer/magnesium hydroxide fire-retardant compositions

Fire-retardant polypropylene (PP) composites were prepared by combining this polymer with uncoated and surface treated forms of magnesium hydroxide filler and various elastomeric modifiers, with and without maleic anhydride functionalization. Mechanical properties of binary and ternary phase compositions differed significantly and are discussed in terms of their microstructures (determined principally by SEM and FTIR) and the relative interaction of the components. Impact strength, in particular, was strongly influenced by the presence of filler surface treatment and the degree of rubbery phase dispersion. FTIR showed that functionalized ethylene–propylene rubber (F-EPR) reacted with the surface of uncoated magnesium hydroxide leading to extensive rubber encapsulation and an improvement in toughness relative to unmodified EPR, which was present in the matrix only as phase dispersed droplets. However, by blending F-EPR with filler surface treated with magnesium stearate, encapsulation was inhibited and the rubber was preferentially dispersed in the PP matrix. This formulation resulted in both improved filler–matrix interaction and enhanced matrix toughening leading to a further increase in impact strength. The effects of material composition on melt flow behavior and UL94 flammability rating, are also reported. © 1996 John Wiley & Sons, Inc.     

A comparative study on different rubbery modifiers: Effect on morphologies,mechanical, and thermal properties of PLA blends

To improve the impact toughness of poly(lactic acid) (PLA), four kinds of rubbery modifiers, including ground tyre rubber (GTR), styrene‐butadiene‐styrene block copolymer (SBS), ethylene‐α‐octene copolymer (EOC) and glycidyl methacrylate grafted EOC (mEOC), were introduced for fabricating the PLA blends. The morphological structures, mechanical properties, thermal stability and thermal decomposition kinetics of pristine PLA and the blends were investigated. Results showed that representative droplet‐matrix structures were observed in the PLA blends, of which the PLA/SBS blend presented the smallest domains while PLA/EOC case had the largest elastomeric particle size. Accordingly, the highest impact toughness and elongation at break were achieved by PLA/SBS blend, whereas the tensile strength and elastic modulus for the blends were all lower than that of pristine PLA. Though the incorporation of rubbery modifiers barely altered the peak temperature of melting, the degrees of crystallinity for blends were declined sharply. The results of thermo gravimetric analysis indicated thermal degradation process of PLA phase was accelerated by rubbery modifiers and evidenced by the relative higher mass conversion at peak temperature. The reaction order of PLA phase for blends calculated by Carrasco method exhibited similar values when compared with control sample. However, the values of activation energy were rather lower than that of pure PLA. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43340.     

Mechanical behavior and structure of rubber modified vinyl ester resins

Vinyl esters are used widely as thermoset matrix materials for reinforced composites; however, they suffer from low‐impact resistance. Substantial enhancement of the toughness of brittle polymers may be achieved by dispersing elastomeric inclusions or rubber particles in the polymer matrix, inducing multiple crazing and shear yielding of the matrix. The main objectives of this work are morphological characterization of vinyl ester/reactive rubber systems and investigation of the mechanical and fracture behavior of these systems. Additional studies focused on rubber endcapped vinyl ester in the absence and presence of added reactive rubber. The initial compatibility of the liquid rubber with the liquid resin was studied. This is a key factor, along with cure conditions, in determination of the possible morphologies, namely, the degree of phase separation and particle size. The initial rubber/resin compatibility was found poor and all attempts to improve it by means of surfactants or ultrasonic treatment have not been successful. The flexure mechanical and fracture behavior of the cured resin/rubber systems was investigated. Three basic types of crack propagation behavior, stable, unstable, and stick‐slip, were observed. Fracture toughness of various resin/rubber systems was evaluated and was found to increase with increased content of rubbery second‐phase material. However, there is some payoff in stiffness and flexural strength of the cured resins. The addition of rubber does not affect the resin toughness at impact conditions. Analysis and interpretation of fractures morphology show that both multiple crazing and external cavitation play an important role in the fracture mechanism of the rubber modified specimens. No shear yielding is evident. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 647–657, 1999     

Toughening of unsaturated polyester and vinyl ester resins with liquid rubbers

A comprehensive study of toughening unsaturated polyster and vinyl ester resins by addition of liquid rubbers was carried out by considering the effects of cure temperature and gel time on final resin/rubber morphology. The objective was to produce a dispersed rubber phase consisting of particles less than 15 μm in diameter with the addition of limited amounts of rubber, so as not to seriously reduce the modulus and strength of the base resin. A variety of liquid rubbers was used including those based on poly(butadiene acrylonitrile), poly(epichlorohydrin), and two poly(acrylates). Fracture toughness of unmodified and rubber modified materials was measured using the compact tension (CT) test geometry. Significant improvements in fracture toughness were achieved with little to no change in Young's modulus or glass transition temperature. With modest rubber additions, the fracture toughness increased up to 62% for the polyester resin and up to 116% for the vinyl ester resin. In general, fracture toughness increases with increases in volume fraction of rubbery second-phase particles. However, results suggest that two-phase particles may be more effective tougheners than single-phase particles. The toughening mechanism appears to depend on the type of rubbery particle morphology present.     

Phase separation of some clear polyblends

By using variations of elution and precipitation techniques, a clear ABS resin is found to be a mixture of a styrene–butadiene rubbery copolymer, a methyl methacrylate–styrene–acrylonitrile copolymer, and a graft of the methyl methacrylate–styrene–acrylonitrile copolymer onto the styrene–butadiene rubber. A clear impact acrylic is separated into a methyl methacrylate–styrene–acrylonitrile copolymer and a methyl methacrylate–butadiene rubbery copolymer. Photomicrographs indicate that clarity in the clear ABS and impact acrylic is achieved by matching refractive indices of the continuous and dispersed polymer phases.     

Toughening polycarbonate with core–shell structured latex particles

The toughness as a function of temperature of polycarbonate modified by blending with core-shell structured latex particles was evalated. Comparisons were made among a commercial core-shell latex (MBS), other core-shell (CS) latexes that incorporated a single component rubbery core, and a new class of interpenetrating polymer network (IPN) core-shell latexes with two elastomers in the core. Notched tensile tests differentiated among the blends in terms of their toughness. The most effective modifier at low temperatures was the commercial MBS latex. The CS latexes produced blends that were only slightly less tough than the MBS blends despite better dispersion of MBS and better adhesion to the matrix. The IPN blends were the least tough at low temperatures; however, at 25°C, a blend with IPN had the highest impact strength. Differences between CS and MBS blends were attributed to differences in the percent of butadiene-containing rubber and the chemical nature of the shell. A comparison among the CS latexes showed that increasing the acrylonitrile content of the shell increased the toughness, and increasing the rubber content or the gel fraction of the core increased the toughness. © 1996 Wiley & Sons, Inc.     

The influence of the internal structure of core–shell particles on poly(vinyl chloride)/(methyl methacrylate–butadiene–styrene) blends

Methyl methacrylate–butadiene–styrene (MBS) core–shell particles were prepared by grafting styrene and methyl methacrylate onto polybutadiene seeds via emulsion polymerization. All the MBS particles were designed with the same chemical composition, similar grafting degree but different internal structures. The difference in internal structure was realized by controlling the ratio of ‘external grafting’ and ‘internal grafting’ of styrene. The work focused on the influence of the internal structure of MBS core–shell particles on the properties of poly(vinyl chloride)/MBS blends. From transmission electron microscopy, three different internal structures were observed: rare sub‐inclusions, a large number of small sub‐inclusions and large sub‐inclusions. The results of dynamic mechanical analysis illustrated that the different internal structures greatly affected the glass transition temperature T_g of the rubber phase and the storage modulus of the core–shell particles. The notched Izod impact test results showed that the MBS with large sub‐inclusions had the lowest brittle–ductile transition temperature, while the transparency test revealed that the presence of sub‐inclusions in the rubbery phase reduced the transparency of the blend. Copyright © 2012 Society of Chemical Industry     

The Influence of NBR-g-GMA Compatibilizer on the Morphology and Mechanical Properties of Poly (ethylene terephthalate)/Polycarbonate/NBR Ternary Blends

The work aims to study the role of NBR-g-GMA compatibilizer on the morphology and mechanical characteristics of PET/PC/NBR ternary blends. The compatibilizer content and amount of constitutive polymers are changed to correlate morphology development with mechanical properties. Various ternary samples are prepared using a twin-screw extruder whereat weight percent of rubbery dispersed phase (NBR+NBR-g-GMA) is changed. Analyzing the morphology of produced samples and interpretation of mechanical properties corroborated the role of the mentioned factors on the type of morphology and also the size of both individual and composite domains in these sorts of ternary blends. Based on this attempt, the mechanical properties of 50/50 blends of NBR/NBR-g-GMA, showed maximum toughness value compared to pure PET specimen. Also, the results revealed that by increasing the rubber content, the rodlike structures were disappeared; besides, toughness was increased. On the contrary, by increasing PC content, rodlike structures have seen by morphological study; however, core-shell droplets formed in the blend structure caused enhancing the impact strength and reducing Young's modulus. Ultimately, the ternary blend of 63/7/30 of PET/PC/ (NBR+NBR-g-GMA) revealed the best mechanical properties due to proper interaction between the PET matrix and rubbery domains in the presence of reactive compatibilizer.     

Surface modification effects of core–shell rubber particles on the toughening of poly(butylene terephthalate)

We toughened poly(butylene terephthalate) (PBT) by loading core–shell rubber (CSR) type impact modifiers, consisting of a rubbery poly(n‐butyl acrylate) core and a rigid poly(methyl methacrylate) shell. To optimize the dispersion of CSR particles into the PBT matrix during melt compounding, the shell surface was modified with different grafting ratios of glycidyl methacrylate (GMA) reactive with PBT chain ends. In PBT blends with a 20 wt % CSR loading, the dispersed rubbery phases showed discernible shapes depending on the grafted GMA content, from predetermined spheres with 0.25 ± 0.05 μm diameters to their aggregates in the 2–3 μm diameter range. As a result, the interparticle spacing (τ) could be controlled from 0.25 to 4.0 μm in the PBT blends containing the fixed rubber loading. The Izod impact strengths of these samples increased significantly below τ = 0.4 μm. Additional thermal and morphological analyses strongly supported the hypothesis that the marked increase in toughness of the blends was related to less ordered lamellar formation of the PBT matrix under the confined geometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synergistic effect of dual rubber system in toughening styrene maleic anhydride copolymers

Styrene maleic anhydride (SMA) copolymers were toughened by blending with two distinctly different rubber modifiers: styrene‐butadiene‐styrene (SBS) block copolymer and methacrylated butadiene‐styrene emulsion‐made graft copolymer (MBS). The modifiers were used both individually and in combination for the examination of their roles in toughening SMA. SMA was miscible with poly(methylmethacrylate) shell of MBS, whereas it was partially miscible with the polystyrene (PS) phase of SBS. When 40–50% of SBS was used in blends, the PS phase of SBS became immiscible with SMA. SBS did not improve the Izod impact strength of SMA appreciably. A prominent synergistic toughening effect was experimentally observed when SBS and MBS were used in combination in brittle SMA. This effect may be attributed to the fact that the large SBS particles initiate crazes and small MBS particles with good adhesion to SMA matrix improve the ligament thickness, which may play a critical role in craze growth and termination. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2260–2267, 2003     

Morphology and toughness characterization of epoxy resins modified with amine and carboxyl terminated rubbers

The morphology (dispersed phase composition, size distribution, and particle/matrix interface shapes) of epoxy resins modified with 5–15 parts by weight (pbw) of carboxyl (CTBN) and amine (ATBN) terminated butadiene acrylonitrile rubber have been characterized. The characterization techniques were transmission electron microscopy coupled with energy dispersive X-ray analysis, differential scanning calorimetry and proton and ¹³C nuclear magnetic resonance. ATBN modified epoxies have a diffuse-appearing interface between the dispersed rubber phase and the epoxy matrix, in contrast to the sharp boundaries of CTBN particle interfaces. Interface mixing of epoxy and rubber, hypothesized initially to explain the interface diffuseness in ATBN modified epoxy, was not found in either CTBN or ATBN modified epoxy. The difference in interface appearance is attributed to ATBN particles having highly irregular shapes compared to the nearly spherical CTBN particles. Bimodal particle size distributions are observed with both modifiers. Both rubber modifiers also produce essentially identical toughness values which do not increase with rubber content in the range 5–15 pbw despite a commensurate increase in the population of large particles.     

Comparison of some butadiene-based impact modifiers for polycarbonate

The relationship of blend morphology to deformation mechanisms and notched Izod impact strength was studied with three butadiene-based impact modifiers for polycarbonate (PC). The impact modifiers were a linear polybutadiene (PB), a styrene–butadiene–styrene block copolymer (SBS), and a structured latex particle having a PB core and methyl methacrylate/styrene shell (MBS). The particle-size distribution in the blends was determined from transmission electron micrographs (TEM). Fractographic analysis combined with TEM examination of thin sections from impacted specimens provided insight into the failure mechanisms. Good impact was achieved with PC/MBS blends when cavitation of the core–shell particles relieved triaxiality and enabled the matrix to fracture by the plane stress ductile tearing mode that is characteristic of thin PC. The best impact properties were obtained with PC/SBS blends when the modifier was dispersed as aggregates of small particles. Cavitation at the weak internal boundaries relieved triaxiality, but subsequent coalescence of cavitated particles during ductile drawing of the matrix created critical size voids and the resulting secondary cracks reduced the toughness of the blend. In general, PB did not significantly enhance the impact strength of PC. © 1994 John Wiley & Sons, Inc.     

Toughening of vinyl ester resin using butadiene-acrylonitrile rubber modifiers

A common method for toughening thermoset resins is the addition of butadiene-acrylonitrile based rubber modifiers. A difficulty experienced by diglycidyl ether of bisphenol-A (DGEBA) vinyl esters (VE) compared to other thermosets is the solubility of the butadiene-acrylonitrile modifier. In this study, a miscible system was prepared by reducing the VE monomer molecular weight to 540 g/mol from industrially used monomers possessing molecular weights greater than 700 g/mol. A main objective of this study was to toughen the vinyl ester while limiting plasticization by varying rubber reactivity and concentration. All modified samples experienced a significant increase in fracture toughness with some degree of plasticization, as shown by losses in modulus and glass transition temperature (T_g). Epoxy terminated rubber (ETBN) yielded a higher toughness than vinyl terminated rubber (VTBN) due to the difference in rubber particle formation and resulting morphology. Chemical linkage of VTBN to the vinyl ester matrix hindered complete phase separation, but helped the retention of mechanical properties when compared to ETBN.     

苯乙烯在MBS中的结合方式对PVC/MBS性能的影响

以乳液聚合法合成了化学组成恒定的具有核-壳结构的(甲基丙烯酸甲酯/丁二烯/苯乙烯)共聚物(MBS),通过改变原料及其配比,使苯乙烯(St)在MBS中以共聚或接枝方式结合,用动态力学热分析仪研究了MBS内耗与温度的关系。将MBS与聚氯乙烯(PVC)共混,研究了St结合方式对共混物冲击韧性及增韧机理的影响,结果表明,随着MBS核中St含量的增加,PVC/MBS共混物的脆-韧转变向高温移动;当St仅以接枝的方式结合时,橡胶粒子的空洞化及剪切屈服是主要的增韧机理,当St仅以共聚方式结合时,剪切屈服是主要的增韧机理。     

Rubber-modified epoxy resins containing high functionality acrylic elastomers

The effect of the functionality of n-butylacrylate/acrylic acid copolymers upon the impact resistance of epoxy resins modified with these rubbery copolymers as a second phase was investigated using a high speed tensile test and scanning electron microscopy. It was found that an optimum functionality of copolymer existed for maximum impact resistance. This optimum value was the result of the competition between the amount of rubber–matrix reaction, an increases in which tended to increase toughness, and solubility of the rubber in the epoxy matrix, which eventually decreased toughness.     

PVC抗冲改性机理和新型PVC冲击改性剂的设计

对PVC冲击改性剂——MBS、CPE和ACR的分子组成和分子结构进行了分析,研究了其抗冲改性机理及对PVC制品低温冲击强度、耐候性、维卡软化点、韧性的影响。从高分子热力学的角度分析了CPE和ACR在PVC中分散所形成的制品结构。指明了传统ACR和CPE在PVC改性中所存在的优缺点。在此基础上分析了理想冲击改性剂ACR应具有的结构特点,并设计和开发了新型冲击改性剂ACRHL-56和HL-58,通过试验对其性能与传统冲击改性剂ACR和CPE进行了比较,发现其性能远优于后者。     

核—壳共聚物对光盘级聚碳酸酯的增韧研究

研究了甲基丙烯酸甲酯－丁二烯－苯乙烯共聚物（MBS）对光盘级聚碳酸酯的增韧作用，结果表明，MBS对PC增韧效果显著，且MBS分散性越好，达到晚一韧转变时所需的MBS含量越少，求得达到脆－韧转变时的临界粒间距为50nm，对共混物损伤机制的研究表明，MBS增韧PC共混物的增韧机理为MBS粒子的空洞化引发基体的剪切屈服。     

Crystalline morphology of polypropylene and rubber-modified polypropylene

The crystalline morphology of injection-molded polypropylene (PP), its relationship with crazing, and the effects of various impact modifiers on the morphology, crystallization, and fusion of PP have been studied. The highly oriented skin layer of an injection-molded tensile bar after deformation was found to be free from crazing in contrast to the heavy craze density in the randomly oriented spherulitic core zone. Reasons for the difficulty in craze nucleation in a preoriented zone are given in light of Argon's theory of craze initiation. Addition of a rubbery phase results in an irregular texture of spherulite, smaller spherulitic diameter, and decrease in the degree of undercooling, but no appreciable change in heats of fusion and crystallization other than a trivial volume effect. The rubbery phase is not pushed by the melt–solid interface to relocate to the interspherulitic boundaries. Rather, it is engulfed by the growing melt–solid interface, leaving behind a random spatial distribution of rubber particles in the PP matrix.     

The toughness and morphology of (chlorinated poly[vinyl chloride])/(methyl methacrylate‐butadiene‐styrene) blends

A series of methyl methacrylate‐butadiene‐styrene (MBS) graft copolymers were synthesized via seeded emulsion polymerization techniques by grafting styrene and methyl methacrylate on poly(butadiene‐co‐styrene) (SBR) particles. The chlorinated poly(vinyl chloride) (CPVC)/MBS blends were obtained by melting MBS graft copolymers with CPVC resin, and the effect of the core/shell ratio of MBS graft copolymer and SBR content of CPVC/MBS blends on the mechanical properties and morphology of CPVC/MBS blends was studied. The results showed that, with the increase in the core/shell ratio, the impact strength of the blend increased and then decreased. It was found that, when the core/shell ratio was 50/50, the impact strength was about 155 J/m, and the tensile strength evidently increased. The toughness of the CPVC/MBS blend was closely related to the SBR content of the blend, and with the increasing of SBR content of blend, the impact strength of the blend increased. The morphology of CPVC/MBS blends was observed via scanning electron microscopy. Scanning electron microscopy indicated that the toughness of CPVC/MBS blend was consistence with the dispersion of MBS graft copolymers in the CPVC matrix. J. VINYL ADDIT. TECHNOL., 22:501–505, 2016. © 2015 Society of Plastics Engineers     

Impact reinforcement of poly(vinyl chloride)

Several theories have been advanced to explain the toughening of glassy plastics by rubbery modifiers. These have been based primarily on studies of high impact polystyrene or ABS systems, where the crazing mechanism has been shown to be most applicable. In the present study, the effects of MBS (methacrylate-butadiene-styrene) impact modifiers on PVC have been studied, utilizing both physical and microscopic techniques. Tensile test results indicate that a primary contribution of the modifier to increased toughness is a lowering of the yield stress of the PVC. Electron microscopic studies and density determinations on strained samples indicate no crazes in these MBS-modified PVC systems. These results suggest that the mechanism of impact reinforcement in PVC is based on the enhancement of localized yielding in the vicinity of the rubbery modifier particles.