Phase morphology and dynamic mechanical behavior for MIS toughened polyvinyl chloride

Graft copolymers of isoprene (Is), styrene (St), and methyl methacrylate (MMA) monomers (MIS) with typical core–shell structure were synthesized by seed emulsion polymerization and used as a toughening agent for preparation of polyvinyl chloride (PVC)/MIS blends. The St and MMA monomers were separately grafted on the cross‐linked poly‐isoprene rubber core. The toughness, sub‐micro‐morphology, and dynamic mechanical behavior of the blends were characterized by impact machine, scanning electron microscopy (SEM), and dynamic mechanical analyzer. The results showed that the impact strength of the blends was optimized when the content of MIS in PVC/MIS blends was kept at a constant value of 8 wt %, while the content of Is in MIS was 70 wt %. SEM morphologies of impact fractured surface showed that the PVC/MIS blends were typical ductile fracture because of the toughness effect of rubber particles, which correlated well with the mechanical properties. Under the same rubber content condition, the curves of the dynamic mechanical behavior of MIS toughened PVC blends appeared a more obvious rubber peak, indicating that the rubber content of MIS was higher than that of methyl methacrylate–butadiene–styrene (MBS), which explained the better toughening effect of MIS compared with MBS. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Toughening of polyvinylchloride by methyl methacrylate–butadiene–styrene core–shell rubber particles: Influence of rubber particle size

An analysis was made on the effects of rubber particle size on the mechanical properties and deformation mechanisms of transparent polyvinyl chloride (PVC) blends containing core–shell methyl methacrylate–butadiene–styrene (MBS) impact modifiers. The critical interparticle distance was found not to be the criterion for the brittle‐ductile transition in the blends. In tensile tests, the blends with larger (100–280 nm) rubber particles exhibited intense stress‐whitening, while one blend with small (83 nm) rubber particles showed only slight stress‐whitening. These differences were due to an increase in resistance to cavitation with decreasing rubber particle size. Transmission electron microscopy studies on blends with a bimodal distribution of particle sizes showed that in the whitened zone of Izod specimens the larger rubber particles cavitated and expanded on yielding, while the smaller particles remained intact. However, Izod test results showed that small MBS rubber particles can toughen the PVC matrix very effectively, especially at low temperatures and at low rubber concentrations. The deformation mechanisms responsible for these effects were discussed. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Epoxy networks toughened by core–Shell particles: Influence of the particle structure and size on the rheological and mechanical properties

The core–shell particles considered were poly(butyl acrylate) core/epoxy groups functionalizing the poly(methyl methacrylate) shell. Physical and thermomechanical properties of benzyl dimethylamine (BDMA)‐catalyzed diglycidyl ether of bisphenol A (DGEBA)/dicyandiamine epoxy networks toughened with core–shell particles were studied. The blends were prepared under well‐defined processing conditions. The resulting properties were found to depend on the state of the dispersion of the particles in the prepolymer matrix before crosslinking. These particles were dispersed at different volume fractions in order to vary the interparticle distance. The relationships between the size of the core–shell particles and the level of toughening are reported. Static mechanical tests were performed in tension and compression modes on these core–shell polyepoxy blends. A slight decrease in the Young's modulus and an increase in the ability to plastic deformation were observed. Using linear fracture mechanics (LEFM), an improvement of the fracture properties (K_IC) was measured. By varying the volume fraction of core–shell particles, an optimum toughness improvement was found for an interparticle distance equal to 400 nm (with an average particle size of 600 nm). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 849–858, 1999     

Toughening modification of PS with n‐BA/MMA/styrene core–shell structured copolymer from emulsifier‐free emulsion polymerization

Core–shell structured particles, which comprise the rubbery core and glassy layers, were prepared by emulsifier‐free emulsion polymerization of poly(n‐butyl acrylate/methyl methacrylate)/polystyrene [P(n‐BA/MMA)/PS]. The particle diameter was about 0.22 μm, and the rubbery core was uncrosslinked and lightly crosslinked, respectively. The smaller core–shell structured particle–toughened PS blends were investigated in detail. The dynamic mechanical behavior and observation by scanning electron microscopy of the modified blend system with core–shell structured particles indicated good compatibility between PS and the particles, which is the necessary qualification for an effective toughening modifier. Notched‐impact strength and related mechanical properties were measured for further evaluation of the toughening efficiency. The notched‐impact strength of the toughened PS blends with uncrosslinked particles reached almost sixfold higher than that of the untoughened PS when 15 phr of the core–shell structured particles was added. For the crosslinked particles the toughening effect for PS was not obvious. The toughening mechanism for these smaller particles also is discussed in this article. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1290–1297, 2003     

Effect of the composition of structured rubber particles on the toughness of poly(methylmethacrylate)

Composite natural rubber (NR) and monodisperse poly(n-butylacrylate) (PBuA) based latex particles were tested as possible impact modifiers for a poly(methylmethacrylate) (PMMA) matrix. A continuous extrusion process was used for the incorporation of wet latexes directly into a twin-screw extruder. All latexes had been coated by a PMMA shell. Furthermore, polystyrene (PS) subinclusions were introduced into the NR core. The impact resistance of the prepared PMMA blends can be most effectively improved by NR particles containing a large weight fraction of compatibilising PMMA in the shell. The degree of crosslinking of the shell polymer has to be restricted. PBuA based latex particles of 180 nm in size are ineffective to toughen the PMMA matrix. The degree of grafting of the NR phase in core–shell particles containing PS subinclusions is not crucial. Scanning electron microscopy was used to analyse the failure processes in composite rubber particle toughened PMMA blends at fast (impact conditions) and slow (tensile testing) deformation speeds.     

Core–shell particles designed for toughening poly(vinyl chloride)

A novel core–shell modifier (MOD) made up of polystyrene and poly(butyl acrylate) (PBA) grafted on a crosslinked styrene‐co‐butadiene core was synthesized by emulsion polymerization. This modifier was used for enhancing effectively the impact ductility of poly(vinyl chloride) (PVC) without losing its transparency. The effects of the MOD on the properties of PVC/MOD blends were explored. It was found that the butyl acrylate (BA) content of the MOD was an important factor affecting the properties of PVC/MOD blends. The Izod impact strength of these blends reached 1200 J m^?1 when the MOD contained 40 wt% BA. The dispersion morphology of the MOD in the PVC matrix was investigated using transmission electron microscopy, with a uniform dispersion of the MOD with higher BA content being obtained. The toughening mechanism of PVC/MOD blends was also investigated. The presence of BA in the MOD enhanced the ductility of the PVC blends due to the increased amount of soft phase (PBA). The dispersion morphology indicated that the interfacial interaction between MOD particles and PVC matrix was improved due to the presence of PBA graft chain in the MOD. TEM of impact fracture samples showed that shear yielding of the PVC matrix and debonding of MOD particles were the major toughening mechanisms for the PVC/MOD blends. Copyright © 2010 Society of Chemical Industry     

Effect of the core‐shell impact modifier shell thickness on toughening PVC

The shell thickness of a core/shell impact modifier is found to be the single most important factor in the toughening of rigid polyvinyl chloride (PVC). When the shell thickness is greater than a critical value of 15.8 nm, these core‐shell elastomeric particles are able to remain structurally intact and well dispersed within the PVC matrix after melt blending. However, too thick a shell thickness results in a hard core (high modulus) of these core/shell particles and loss of the rubbery nature required of an efficient impact modifier. Therefore, these over‐thick particles can act only as rigid fillers, not as efficient rubbery modifiers. On the other hand, when the shell thickness is less than the critical value of 4.9 nm, too thin a shell layer is simply unable to fully protect and cover the inner rubbery core during vigorous processing conditions, and these core‐shell particles tend to connect with one another through the partially exposed core to form a cellular‐like structure, thus resulting in poor toughening efficiency. Regardless of the particle size, as long as the shell thickness of these core/shell elastomers is between these two critical values (15.8 nm and 4.9 nm), they all display high efficiency in toughening rigid PVC. Polym. Eng. Sci. 44:1885–1889, 2004. © 2004 Society of Plastics Engineers.     

Blends containing core–shell impact modifiers. Part 3 – Effects of temperature on tensile impact behaviour

Abstract

The performances of two contrasting core–shell impact modifiers, in blends with polycarbonate (PC), poly (methyl methacrylate) (PMMA), and poly (styrene-co-acrylonitrile) (PSAN), have been evaluated using tensile impact tests at temperatures between -80 and +50°C. In both modifiers, each individual particle has a 10 nm thick outer shell of PMMA, which is grafted to the rubber phase. In the case of modifier PB, the core of the particle is a 200 nm diameter homogeneous sphere of polybutadiene, with a T _g of -86°C. Modifier PBA has a 260 nm core of PMMA, surrounded by a 20 nm inner shell of poly (butyl acrylate-co-styrene), which has a T _g of -17°C. Tensile impact tests show that the T _g of the rubber does not necessarily control the brittle–ductile transition temperature T _BD. Both the PC–PB and PC–PBA blends exhibit some ductility at -80°C, although neither blend is as tough as plain PC at any temperature. The blend of PB with PMMA shows a modest increase in toughness above -40°C and there is a similar but rather larger increase in the toughness of the PMMA–PBA above -20°C. In PSAN blends, the PBA modifier is the more effective toughening agent ahove 0°C. It is concluded that these differences originate from differences in the balance between shear yielding and crazing in the matrix polymer, and in the ability of cavitated rubber particles to prevent crazes from turning into cracks. In PMMA and PSAN blends, the PBA modifier is the more effective toughening agent at 23°C because of its rigid core, which enables stable rubber fibrils both to form and to contribute to local strain hardening, thereby stabilising the yield zone.     

Preparation and characterization of poly(butadiene-stat-styrene)/poly(styrene-stat-acrylonitrile) structured latex particles

In rubber toughening of thermoplastics, core/shell polymers have been used extensively. This work introduces the synthesis and characterization of polybutadiene based core/shell latex particles with controlled particle size and crosslinking density of the core. A lithium soap recipe was employed to prepare a series of poly(butadiene-stat-styrene) (90/10 by wt) core particles by conventional emulsion polymerization through a batch process. The shell polymer, poly(styrene-stat-acrylonitrile) (72/28 by wt), was polymerized by a semicontinuous process in the presence of the core particles to form a core/shell morphology. The effects of initiator concentration, monomer feeding rate, core/shell ratio, and gel-fraction of the core on the core/shell particle morphology were studied. The degree of grafting of the shell polymer on the core particles was determined as well. The morphology and glass transitions of these particles were characterized by transmission electron microscopy, differential scanning calorimetry, and dynamic mechanical spectroscopy. These latex particles can be used specifically in toughening polycarbonate. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1123–1134, 1997     

Damage zone in PVC and PVC/MBS blends. I. The effect of rubber content and temperature

The damage zone development in poly (vinyl chloride) (PVC) and its transparent blends with methyl methacrylate-butadiene-styrene (MBS) core/shell rubber was studied as a function of temperature and rubber content in a triaxial stress state under slow tensile loading. Failure at the semicircular notch occurred by shear yielding followed by stress whitening. In unmodified PVC, the shear yielded plastic zone size was not affected by temperature in the range between —40 and 40°. In the blends, the plastic zone preceding stress whitening increased in size with temperature and rubber content, shifting the stress-whitened zone further away from the notch root. Below 0°, stress whitening initiated at the notch root and the stress-whitened zones had a crescent shape similar to those of PVC/CPE blends studied previously. In unmodified PVC, stress whitening initiated from the growth of preexisting microvoids at the tip of the shear yielded zone containing two families of curving slip lines emanating from the notch root. In contrast, stress whitening in the blends was more intense and was initiated by the cavitation of the rubber particles.     

Toughening of polycarbonate: Effect of particle size and rubber phase contents of the core‐shell impact modifier

The toughening behavior of polycarbonate modified with core‐shell type particles was investigated. The alloys were found to exhibit maximum impact strength upon addition of a modifier with a poly(butyl acrylate) rubbery core of 0.25 μm diameter. The incorporation of particles with diameter greater than 0.25 μm resulted in decreased impact strength. The influence of rubber phase contents on toughness was also studied. It was observed that the alloys exhibited maximum impact strength upon addition of 4 wt % rubber phase. Further increase in the rubber phase content resulted in reduced impact strength. Fractography of the samples showed that, below 4 wt % rubber phase content, the fracture occurs mainly by internal crazing and, from 4 wt % onward, only by shear deformation. When the effect of dual particle size distribution was analyzed, it was found that there was only a moderate increase in toughness compared with alloys containing monosized particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 748–755, 2005     

一种新型交联剂对ACR增韧PVC的影响

采用二甲基丙烯酸乙二醇酯（EGDMA）作为一种新型交联剂,以种子乳液聚合方法合成了一系列不同交联剂含量的丙烯酸酯类核壳增韧改性剂（ACR）,用于对聚氯乙烯（PVC）树脂的增韧改性研究。通过改变交联剂的含量,测试了ACR的交联度、接枝度、接枝效率和玻璃化转变温度（Tg）。研究了ACR/PVC共混物的力学性能与交联剂含量之间的关系。数据显示：当交联剂含量增加时,ACR的交联度、接枝度、接枝效率和玻璃化转变温度都得到了升高。当交联剂含量为0.4%,ACR/PVC的质量比为8/100时,ACR/PVC共混物发生了脆韧转变,冲击强度为1145J/m,是纯PVC的39倍。     

Effects of core‐shell acrylate particles on impact properties of chlorinated polyethylene/polyvinyl chloride blends

The impact properties of core‐shell acrylate (CS‐ACR)/chlorinated polyethylene (CPE)/poly(vinyl chloride) (PVC) blends under different temperatures were investigated. The fracture surface morphologies of the blends were observed by scanning electron microscopy (SEM). The results show that there exists significant synergistic effect between CS‐ACR particles and CPE in toughening PVC, and the impact properties of the blends generally correlate well with SEM morphologies. Besides, with increasing CS‐ACR content, ductile–brittle transition point of the ternary blends remarkably shifts to a lower temperature. Dynamic mechanical analysis exhibited that intensity and area of low‐temperature tan δ peaks of the CPE/PVC blends increase obviously after the addition of CS‐ACR particles, which to some extent are just in line with the changes in impact strength and ductile–brittle transition point of the blends. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Influence of core–shell particles structure on the morphology and brittle‐ductile transition of PBT/ABS‐g‐GMA blends

The performance of glycidyl methacrylate (GMA) functionalized acrylonitrile‐butadiene‐styrene core–shell impact modifiers (R‐ABS) with varied GMA content, crosslinking degree of rubber phase, core–shell ratio, and initiator type in toughening of poly(butylene terephthalate) (PBT) was investigated. Results show that 1 wt% GMA is sufficient to induce a pronounced improvement of the impact strength of PBT and too much GMA induces the crosslinking of R‐ABS. Divinylbenzene improves the crosslinking degree of polybutadiene and decreases its cavitation ability. The brittle‐ductile transition shifts to higher R‐ABS content. When the core–shell ratio of R‐ABS is beyond 70/30, compatibilization reaction is not sufficient to retard the agglomeration of core–shell particles. R‐ABS particles with the core–shell ratio between 50/50 and 60/40 are suitable. Initiator type can influence the internal structure of R‐ABS. For R‐ABS prepared with azobisisobutyronitrile (AIBN) as initiator, big subinclusion structure decreases its toughening ability. R‐ABS prepared with redox initiator shows better toughening behavior. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Core-shell structured latex particles. III. Structure–properties relationship in toughening of polycarbonate with poly(n-butyl acrylate)/poly(benzyl methacrylate–styrene) structured latex particles

The performance of the designed structured core-shell latex particles in toughening polycarbonate (PC) matrix was examined. Izod impact testing of the PC-core-shell latex blends were used to evaluate the influence of parameters related to the core-shell latex particles on toughening polycarbonate. Among these parameters are the particle size and levels of crosslinking of the core rubber particles, composition and molecular weight of the shell polymer, and weight ratio of shell to core polymers as well as the particle morphology. In this work, core-shell structured latex particles with thinner shells of higher molecular weight polymers were found to improve the impact resistance of polycarbonate. The role of chain entanglements in increased adhesion between the discrete rubbery phase and the continuous glassy matrix and the importance of surface-to-surface interparticle distance for toughening at various temperatures are discussed. © 1995 John Wiley & Sons, Inc.     

The use of latex rubber-modified polystyrene as a model system for HIPS: Effect of particle size

The effect of particle size in high-impact polystyrene (HIPS) is difficult to determine because of a size polydispersity and changes in particle morphology during the HIPS synthesis process. In this study, poly(n-butyl acrylate) rubber core/polystyrene shell particles were made by emulsion polymerization methods such that the only difference was in particle diameter, which ranged from 0.4 to 6.2 μm. The latexes were subsequently incorporated into a polystyrene matrix to form a toughened composite that acted as a simple model for HIPS. Charpy impact energies (notched and unnotched) of the composites showed that there was no toughening for particle sizes less than 2μm in diameter. The optimal impact energy was obtained with particle diameters in the region of 2–3 μm at 8 wt % rubber loading. The results imply that craze stabilization is the most important aspect of the toughening process. A simple toughening model based on the crack opening displacement of craze breakdown between adjacent rubber particles is suggested, with interparticle distance as the most important variable. © 1993 John Wiley & Sons, Inc.     

Effects of core‐shell particle growth manners on morphologies and properties of poly(vinyl chloride)/(methyl methacrylate–butadiene–styrene) blends

A series of methyl methacrylate‐butadiene‐styrene (MBS) core‐shell particles were synthesized by seeded emulsion polymerization. All the MBS particles are designed with the same defined chemical composition, which is a prerequisite for producing transparent blends with poly(vinyl chloride) (PVC). Three different growth manners of core‐shell particles: agglomeration of small styrene‐butadiene rubbers (SBRs) followed by styrene (ST) and methyl methacrylate (MMA) monomers grafting, agglomeration of small MBS particles and traditional MBS with single SBR rubber core, and ST/MMA shells are used. The effects of growth manners of MBS on the properties and deformation mechanism of PVC/MBS blends are studied. It is found that all the MBS particles can toughen the PVC matrix effectively, but different deformation modes are observed: cavitation in large particles, debonding at the PVC/MBS interface, rubber cavitation, and clusters of voids, respectively. In addition, it is found that the stress‐whitening extent is associated with the deformation modes. J. VINYL ADDIT. TECHNOL., 22:37–42, 2016. © 2014 Society of Plastics Engineers     

Synthesis and characterization of poly(butyl acrylate‐co‐ethylhexyl acrylate)/ poly(vinyl chloride)[P(BA‐EHA)/PVC] novel core‐shell modifier and its impact modification for a poly(vinyl chloride)‐based blend

Synthesis of poly(butyl acrylate‐co‐ethylhexyl acrylate)‐core/poly(vinyl chloride)‐shell [P(BA‐EHA)/PVC] used as a modifying agent of PVC via semicontinuous seeded emulsion copolymerization is reported here. Diameter distributions and morphology of the composite latex particles were characterized with the aid of particle size analyzer and transmission electron microscopy (TEM). The grafting efficiency (GE) and grafting ratio (GR) of vinyl chloride (VC) grafted onto the P(BA‐EHA) with varying content of crosslinking agent and core‐shell ratios were investigated. TEM studies indicated that the P(BA‐EHA)/PVC latex particles have core‐shell structure, and the P(BA‐EHA) rubbery particles in blending materials were uniformly dispersed in PVC matrix. Dynamic mechanical analysis (DMA) results revealed that the compatibility between the P(BA‐EHA) and the PVC matrix was significantly improved due to the presence of the P(BA‐EHA)‐grafted‐VC copolymer. The notched impact strength of the blending material with 3 wt% of rubber content was seven times that of the PVC. Linear regressions of mechanical properties as loading of the modifier were made. The resulting data of notched impact strength and elongation at break for the blending materials deviated significantly from regression lines within 3–4.5 wt% of the P(BA‐EHA) content. The PVC blends modified by the modifier exhibited good toughness and easy processability. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Toughness,dynamic mechanical property,and morphology of polyvinylchloride/acrylonitrile‐styrene‐butyl acrylate blends

Acrylonitrile‐styrene‐butyl acrylate (ASA) graft copolymers with different acrylonitrile (AN) contents, the core‐shell ratio, and tert‐dodecyl mercaptan (TDDM) amounts were synthesized by seed emulsion polymerization. Polyvinylchloride (PVC)/ASA blends were prepared by melt blending ASA graft copolymers with PVC resin. Then the toughness, dynamic mechanical property, and morphology of the PVC/ASA blends were investigated. The results indicated that the impact strength of the PVC/ASA blends increased and then decreased with the increase of the AN content in poly(styrene‐co‐acrylonitrile (SAN) copolymer, and increased with the increase of the core‐shell ratio of ASA. It was shown that brittle‐ductile transition of PVC/ASA blends was dependent on poly(butyl acrylate) (PBA) rubber content in blends and independent of AN content in SAN copolymer. The introduction of TDDM made the toughness of PVC/ASA blends poor. Dynamic mechanical analysis (DMA) curves exhibited that PVC and SAN copolymers were immiscible over the entire AN composition range. From scanning electron microscopy (SEM), it was found that the dispersion of ASA in PVC/ASA blends was dependent on the AN content in SAN copolymer and TDDM amounts. J. VINYL ADDIT. TECHNOL., 22:43–50, 2016. © 2014 Society of Plastics Engineers     

Morphology and rheology relationships of epoxy/core‐shell particle blends

The morphological and rheological behaviors of toughened epoxy resins modified with core‐shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene‐co‐styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl‐functionalized groups (CSf), and second, particles containing no carboxyl‐functionalized groups (CSnf) in the PMMA‐shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near‐zero shear rate occurred in the DGEBA/CSf blend presenting non‐Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles‐particles and the particles‐matrix. The Williams‐Landel‐Ferry (WLF) shift procedure was used to construct modulus master curves G′ and G″ from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network‐type structure. The deviation between theoretical G′ (Paleirne's model) and experimental G′ values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.