Influence of sample thickness on fracture behaviour of a polyketone and a polyketone-rubber blend

The influence of sample thickness on the fracture behaviour of an aliphatic polyketone and a blend of this polymer and 10 wt% core-shell rubber was studied. The sample thickness was varied from 0.1 to 8 mm. The skin morphology was studied by SEM. The fracture behaviour was studied on single edge notch specimen at a high strain rate (30 s⁻¹) in the temperature range of −40 to 120 °C. The fracture stress, fracture strain and fracture energies were determined. The temperature development in the notch area was followed with an Infra Red camera. The cavitation of the rubber particles was studied on tensile bars with a laser setup.With decreasing specimen thickness the fracture energies increased strongly and the brittle-ductile transition shifted to lower temperatures this both for the aliphatic polyketone and the polyketone-rubber blend. The deformation in these materials in accompanied with a strong temperature increase in the deformation zone. The addition of rubber particles decreases the sensitivity towards the thickness. However, in very thin samples the cavitation of the rubber particles is more difficult and the rubber toughening effect decreases. The strong thickness effects on the fracture toughness indicate for both the homo polymer and the blend indicate that data from a standard test with 4 mm thick samples are not representative for thin walled applications.     

Rigid particle toughening of aliphatic polyketone

The influence of precipitated calcium carbonate particles on the toughening behaviour of aliphatic polyketone has been studied. The calcium carbonate particles had a particle size of 0.7 μm and a stearic acid coating (1%). Composites of 0-31.5 vol% CaCO₃ content have been compounded and injection moulded. Studied are the morphology of the composites, the modulus, yield strength, the notch Izod impact strength and the temperature development in the deformation zone by infrared thermography.The thermal properties of the matrix remained unchanged upon addition of CaCO₃. With increasing particle content the modulus increased and the yield strength decreased. This decrease in yield strength is due to the debonding of the particles and was similar as with rubber particles. With increasing particle content the notched impact resistance increased strongly. The notched impact energy at room temperature was increased from 10 to 80 kJ/m² and the brittle-to-ductile transition temperature was lowered to 80 °C. At calcium carbonate contents higher that 16 vol% no further impact improvement was observed. The calcium carbonate particles seemed to debond quite well despite the expected thermal contraction of the matrix polymer. The temperature development in the deformation zone was strong, as strong as with rubber particles. The toughening mechanism with these rigid particles is discussed.     

Deformation mechanisms in rubber toughened semicrystalline polyethylene terephthalate

The deformation mechanisms of rubber toughened polyethylene terephthalate (PET) are studied with fractography of impact fractured samples and tensile dilatometry. The dispersed phase consists of a mixture of an ethylene-co-propylene rubber (EPR) and a compatibilising agent (E-GMA8: copolymer of ethylene and 8 wt% of glycidyl methacrylate). It is found that the ductile fracture behaviour, above the brittle-ductile transition temperature (T_bd), consists of a high degree of rubber cavitation and extensive matrix shear yielding, both in the fracture plane and the stress whitened zone surrounding the crack. A steep increase in the volume strain upon tensile loading confirms the presence of the rubber voiding mechanism in the PET/(EPR/E-GMA8) blend system. It is seen that the stress whitened zone below the impact fracture surface consists of different zones, depending on the test temperature. Below T_bd, a layer of a highly deformed structure is followed by a cavitation layer containing only a limited number of cavitaties. Increasing the temperature, causes the deformation layer to be replaced by a zone lacking structure. It is believed that part of the fracture energy has been dissipated in the form of heat inducing a relaxation in the structure. Dynamical mechanical analysis under superimposed axial stresses reveals that the dispersed rubber particles internally cavitate in the presence of volume strain. At increased volume strains, the biaxial stress state in the cavitated particle is disturbed, resulting in the rupture of the rubber chains closest to the void by a tearing mechanism; revealing that the rubber particle is damaged upon cavitation.     

Influence of copolymerisation on fracture behaviour of aliphatic polyketones

High strain rate tensile impact properties of aliphatic polyketone terpolymers were investigated and related to the polymer chain structure. Aliphatic polyketones were used as a model system, by changing the termonomer content and type. Aliphatic polyketone is a perfectly alternating copolymer and the structure was changed with the addition of a few mol% of termonomer: propylene, hexylene and dodecene. Studied were the thermal properties with DSC and DMTA, tensile behaviour, notched tensile impact behaviour, notched Izod properties and the temperature development during deformation. The perfectly alternating copolymer had a melting point of 257 °C, a T_g at 15 °C, a high crystallinity (48%), a high yield stress (77 MPa) and yield strain (31%) but a relatively low fracture strain (85%) and an impact strength (notched Izod) of 13 kJ/m². Increasing the propylene content to 6%, lowered the melting temperature to 224 °C, without changing the T_g. The modulus and yield stress were lowered but the impact strength improved. Increasing the length of the termonomer while keeping the T_m at 224 °C lowered the T_g, the modulus, the yield stress but strongly improved the impact resistance. The longer termonomers, with a lower yield stress, reduced the necking behaviour. The temperature increase in front of the notch was about 85 °C. By adding termonomers to aliphatic ketones, the notched impact behaviour improved significantly at the cost of modulus and yield stress.     

Structure-property relations of 55 nm particle-toughened epoxy

55-nm rubber particles significantly toughened two epoxy systems without loss of Young’s modulus, tensile strength and glass transition temperature. Transmission Electron Microscopy (TEM) showed that the nanoparticles are uniformly dispersed in matrix and have blurred interface with epoxy. 5 wt% rubber nanoparticles increased the critical strain energy release rate (G_1c) of Jeffamine D230 (J230)-cured epoxy from 175 J/m² to 1710 J/m², while the 10 wt% increased G_1c of diaminodiphenyl sulfone (DDS)-cured epoxy from 73 J/m² to 696 J/m². This is explained by comparing the surface-surface interparticle distance and total particle surface of nanocomposites with those of composites. The higher the matrix stiffness, the more nanoparticles needed for toughening. Although the 10 wt% J230-cured nanocomposite showed a 50% larger size of stress-whitened zone than the 5 wt% J230-cured nanocomposite, the 5 wt% nanocomposite showed a higher toughness. These nanoparticles were found to pose barriers to the vibration of crosslinked matrix molecules, leading to higher glass transition temperatures. While the matrix shear banding caused by nanoparticle expansion and growth is the major toughening mechanism for the J230-cured nanocomposites, the matrix plastic void growth and deformation are most probably the major mechanisms for the DDS-cured system. Under tensile loading, the nanoparticles in the DDS-cured epoxy created fibrils of 100-200 nm in diameter and 3-5 μm in length. TEM analysis in front of a subcritically propagated crack tip showed a number of voids of 30-500 nm in diameter in the vicinity of the crack, implying that rubber nanoparticles expanded, grew and deformed under loading. Unlike conventional epoxy/rubber composites in which all of the rubber particles in the crack front cavitated under loading, only a portion of the nanoparticles in this study expanded to create voids. Huang and Kinloch’s model developed from composites was found not fit well into these nanocomposites.     

Cavitation during tensile deformation of high-density polyethylene

Cavitation process of high-density polyethylene during tensile deformation was studied. It has been shown that the crystallinity and perfection of HDPE crystals govern whether plastic deformation of the polymer is associated with cavitation or deformation occurs without cavitation. The strength of crystals may be controlled by crystallization conditions during preparation of a polymer. If the crystals are thin and the degree of crystallinity is low then the plastic deformation of crystals occurs before reaching the level of stress that initiates cavitation. On the other hand, if the crystals are thick, more perfect, and crystallinity is high, then the cavitation in an amorphous phase is initiated first, and later followed by the deformation of crystals. The cavitation process is usually initiated at the stress level close to the yield point. However, the level of stress necessary for cavitation may be decreased substantially by the orientation of crystalline lamellae, as it was observed in the skin layers of injection-molded material. Voids formed in the skin layer do not influence the yielding process. Typically, cavitation was initiated in volume at the stress of 29-30 MPa, but in the skin of injected samples voids were observed even at the macroscopic stresses of 2 MPa only. The development of voids with deformation was studied both for skin and volume of injection-molded HDPE sample. The shape of voids is strictly connected with deformation of crystalline phase around them.     

Phase separation and mechanical responses of polyurethane nanocomposites

Nanocomposites of a diamine-cured polyurethane with nanofillers of different kinds, sizes, and surfaces were studied. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, tensile tests, and dynamic mechanical thermal analysis were employed in the experiments. Experimental results suggest that mechanical properties are strongly correlated to polymer phase separation, which depends on the nature of the interface between the polymer and the nanoparticles. Two stages of phase separation were observed: the first stage involves the self-assembly of the hard segments into small hard phases of about 10 nm in width; the second stage involves the assembly of the 10 nm wide hard phases into larger domains of about 40-100 nm in width. In the case of polyurethane/ZnO nanocomposites with 5 wt% (less than 1 vol%) 33 nm ZnO nanoparticles, the covalent bonds that were formed between the polymer and ZnO surface hydroxyl groups constrain both stages of phase separation in polyurethane, resulting in approximately 40% decrease in the Young's modulus, 80% decrease in the strain at fracture, and 11 °C increase in the glass transition temperature of the soft segments. In the case of polyurethane/Al₂O₃ nanocomposites with 5 wt% 15 nm Al₂O₃ nanoparticles, hydrogen bonds between the particles and the polymer mainly constrain the second step of the phase separation, resulting in about 30% decrease in the Young's modulus and 12 °C increase in the glass transition temperature, but only a moderate decrease in the strain at fracture. The most striking results come from polyurethane/clay composites, where only van der Waals type interactions exist between polyurethane and the organically modified clay (Cloisite 20A). With the addition of 5 wt% surface modified clay (Cloisite 20A), both the Young's modulus and the strain at fracture decrease more than 80%, but the glass transition temperature increases by about 13 °C. Adding 10 wt% Cloisite 20A into polyurethane almost totally disrupts the phase separation, resulting in a very soft composite that resembles a “viscous liquid” rather than a solid.     

Shrinkage and mechanical properties of unsaturated polyester reinforced with clay and core–shell rubber

Glassy unsaturated polyester (UP) resin was reinforced using an organically modified montmorillonite (OMMT) and toughened with core?Cshell rubber (CSR) particles. The nanostructure, morphology, and deformation mechanism of composite specimens were studied by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and reflected optical microscopy (ROM). An intercalated nanostructure with partial exfoliation was observed in the UP reinforced by various amounts of OMMT. Locally clustered but globally good CSR particle dispersion in the UP matrix was evident in UP toughened with 5 and 10 wt% CSR particles. Simultaneous presence of OMMT and CSR particles in UP/OMMT/CSR hybrid composites was found to cause partial phase separation with bigger rubber particle agglomerates and lower clay-intergallery height increase. The effects of OMMT and CSR contents on volume shrinkage, impact fracture energy, fracture toughness, and compressive yield strength of UP were investigated. The introduction of OMMT of up to 3?wt% into the UP matrix lowered volume shrinkage to some extent, while further addition increased the shrinkage slightly. In the hybrid nanocomposites, the volume shrinkage decreased to a minimum level of 5.2?% with increases in OMMT level. The impact fracture energy of UP improved with increasing the OMMT level of up to 3?wt%, whereas its further addition decreased the impact fracture energy slightly due to the clay particle agglomeration. The hybrid composites with OMMT level below 3?wt% showed higher impact fracture energy compared to the reinforced UP specimens with the same OMMT levels. Interestingly, a synergism in the fracture toughness (K _IC) was observed in the hybrid composite containing 1?wt% OMMT and 10?wt% CSR particles. The presence of OMMT as reinforcement in the hybrid composites could compensate the lowering of the compressive yield strength caused by low-modulus CSR particles. The clay?Crubber particle interaction in the hybrid systems seems to increase the threshold of shear deformation of the UP matrix to some extent.     

Influence of molecular weight on the fracture properties of aliphatic polyketone terpolymers

The influence of polymer molecular weight on the mechanical properties of aliphatic polyketones was investigated. The molecular weight varied from 100,000 to 300,000 g mol⁻¹. The crystallinity was found to be independent of polymer molecular weight, as was the glass transition temperature. The yield strength and stiffness of the aliphatic polyketone terpolymers were also found to be independent of molecular weight. The post yield behaviour showed strong dependency on polymer chain length. The draw stress was increased significantly with higher molecular weight material. The impact resistance was increased with molecular weight, resulting in ductile fractures with large energy consumption upon fracture. The brittle-to-ductile transition temperature was lowered with increasing chain length. The difference in material deformation was linked to the higher mechanical connectivity and more stable post yield behaviour of the polymers with an increased molecular weight.     

Uniaxial deformation of an elastomer nanocomposite containing modified carbon nanofibers by in situ synchrotron X-ray diffraction

Structure and property of a nanocomposite consisting of modified carbon nanofibers (MCNFs), homogenously dispersed in an elastomeric ethylene/propylene (EP) random copolymer (84.3 wt% P) matrix, were studied by in situ synchrotron X-ray diffraction during uniaxial deformation. The MCNF acted as a nucleating agent for crystallization of the α-form of isotactic polypropylene (iPP) in the matrix. During deformation at room temperature, strain-induced crystallization took place, while the transformation from the γ phase to α phase also occurred for both unfilled and 10 wt% MCNF-filled samples. The tensile strength of the filled material was consistently higher than that of pure copolymer. However, when compared with pure copolymer, the highly stretched nanocomposite exhibited a higher amount of unoriented crystals, a lower degree of crystal orientation and a higher amount of γ crystals. This behavior indicated that polymer crystals in the filled nanocomposite experienced a reduced load, suggesting an effective load transfer from the matrix to MCNFs. At elevated temperatures, the presence of MCNFs resulted in a thermally stable physically cross-linked network, which facilitated strain-induced crystallization and led to a remarkable improvement in the mechanical properties. For example, the toughness of the 10 wt% nanocomposite was found to increase by a factor of 150 times at 55 °C.     

Polycarbonate and co-continuous polycarbonate/ABS blends: influence of specimen thickness

The influence of specimen thickness on the fracture behaviour of polycarbonate (PC) and co-continuous PC/ABS (50/50) blends was studied in single edge notch tensile tests at 1 m/s and different temperatures (−80 to 130 °C). Specimen thickness ranged from 0.1 to 8 mm. In the co-continuous PC/ABS blends the rubber concentration in the ABS was 0, 15 and 30 wt%. The change in fracture toughness was typified by the change in brittle-to-ductile transition temperature (T_bd).T_bd of pure PC depended strongly on specimen thickness, leading to very low transition temperatures for thin PC specimens. PC/ABS 0%, a 50/50 blend of PC and SAN (i.e. ABS without polybutadiene (PB)), was a brittle blend and showed a very high T_bd close to the T_g of SAN. T_bd did not seem to be influenced by specimen thickness. PC/ABS blends with 15 and 30% PB in ABS showed improved T_bd compared to PC/SAN and PC, indicating effective rubber toughening. T_bd decreased with decreasing thickness for PC/ABS specimens thicker than 1.5 mm. However, T_bd increased with decreasing thickness for specimens below 1.5 mm thickness. In thin specimens, the rubber-filled blend is less effective rubber toughening. The plane strain stress condition needed for rubber cavitation is apparently not present in thin specimens.     

Filler/matrix-debonding and micro-mechanisms of deformation in particulate filled polypropylene composites under tension

Volume strain measurements of particulate filled polypropylene (PP) composites containing different glass beads and talc as filler were carried out in tension as a function of temperature and strain rate to determine the micro-mechanisms of deformation. While local cavitation mechanisms (micro-voiding, crazing, and micro-cracking) and subsequent debonding of the particles dominated as failure mechanisms at high strain rates and at room temperature, a more significant contribution of local shear yielding was observed with a reduced contribution of cavitational mechanisms at low strain rates or at 80 °C. This change in the dominating micro-mechanisms of deformation resulted in smaller volume strains during the tensile loading of the composites than for the respective neat matrix. Moreover, a novel approach is introduced for the detection of debonding using volume strain measurements, which takes into account the dilatational and deviatoric behavior of the neat matrix polymer and the composite. The results are supported by acoustic emission measurements carried out simultaneously on the same specimens.     

Effect of loading-rate on fracture micromechanism of methylmethacrylate-butadiene-styrene polymer blend

Methylmethacrylate-butadiene-styrene (MBS) polymer blends having two different types of rubber particle distribution, monomodal and bimodal, were prepared, and their fracture properties and fracture mechanisms were investigated under quasi-static and impact loading. A fracture property, maximum J-integral J_max, was evaluated at both loading-rates, and it was shown that J_max values of the bimodal MBSs are much greater than that of the monomodal with small particles, and slightly better than that of the monomodal with large particles. Thick damage zones were observed in the crack-tip regions in the bimodal and monomodal with large particles, indicating larger energy dissipation during fracture initiation than in the monomodal with small particles in which damage zone is much thinner. TEM micrographs exhibit that extensive plastic deformation under quasi-static rate and multiple craze formation under impact loading rate are the primary toughening mechanisms in the bimodal MBS blends. By assessing both fracture properties and transparency, the bimodal blend with blend ratio: 2.5/7.5 (=140 nm/2.35 μm; total rubber particle content is 10 wt%) was proved to show the best performance as MBS polymer blend with satisfiable transparency and high fracture resistance.     

A constitutive model for the nonlinear viscoplastic behavior of thermoplastic olefin

A tangent constitutive model was developed in this article to address the nonlinear viscoplastic behavior of compound grade thermoplastic olefin (TPO). The TPO was commonly blends of polypropylene matrix, rubber, and inorganic filler. The constitutive model for TPO was obtained from the combination of the mechanical behavior of the matrix and fillers. In a multiphase material, the rate‐dependent behavior of polypropylene matrix was presented by a physically based constitutive model for large strain deformation, while the deformation behavior of rubber and talc were captured by Hooke's law. The average strain of each phase, as well as the strain of the voids caused by cavitation of rubber and debonding of talc, was determined by the Mori‐Tanaka method, in conjunction with a tangent modulus approach. To test the applicability of the developed model, it was applied to calculate the rate dependent stress‐strain relations of TPO. The model was predictive of the initial rate‐dependent stiffness, yield, and strain hardening response in large strain deformation. The constitutive model was incorporated into a finite element code to predict the large strain deformation behavior of TPO. The initiation of necking and neck propagation were obtained and confirmed by experimental observation. POLYM COMPOS., 2010. © 2009 Society of Plastics Engineers     

Plane stress fracture toughness of physically aged plasticized PETG as assessed by the essential work of fracture (EWF) method

The plane stress fracture toughness of amorphous copolyester (PETG) sheets plasticized by various amount of neopentylglycol dibenzoate (NPGDB in 0, 5, 10 and 20 wt%) was studied in as-received (AR) and rejuvenated (RJ) states by adopting the essential work of fracture (EWF) method. EWF tests were performed on deeply double-edge notched tensile loaded (DDEN-T) specimens at various deformation rates (2,10 and 100 mm/min) at room temperature. It was established that physical aging strongly affected the EWF terms. The specific yielding-related EWF increased with increasing deformation rate and decreased with increasing plasticizer content. The specific non-essential work and its necking-related constituent, which changed parallel to each other, remained constant up to 10 wt% NPGDB content and decreased afterwards. The plastic zone in the DDEN-T specimens was formed by cold drawing which is governed by the entanglement structure. This was demonstrated by the shape recovery of the plastic zone in the broken DDEN-T specimens after heating them above the T_g of the related PETG compound.     

Microstructural design and high temperature tensile deformation behaviour of 8 mol% yttria stabilized cubic zirconia (8YCSZ) with SiO2 additions

In the present study, the microstructural evolution and high temperature deformation behaviours of 8 mol% Y₂O₃ stabilized cubic zirconia (8YCSZ) containing up to 10 wt% SiO₂ is investigated. The experimental results show that the SiO₂ doped specimens sintered at 1400 °C contain only the cubic crystalline phase and SiO₂ has the very limited solubility of 0.3 wt% in cubic zirconia. This suggests that only small part of the SiO₂ dissolves in the cubic zirconia and the rest of SiO₂ segregates at grain boundaries and multiple junctions as amorphous (glassy) phase. This glassy phase prevents the grain growth by minimizing grain boundary energy and mobility, which results from solute segregation at the grain boundary and its drag. The deformation of the undoped 8YCSZ is characterized by large strain hardening with limited elongation. This is mainly due to severe grain growth during high temperature deformation. The addition of the SiO₂ results in a decrease in strain hardening and enhanced tensile elongation. These effects have been further improved with the increase of the SiO₂ addition reaching the elongation to failure of 152% for 10 wt% SiO₂ doped specimen in tension at a temperature of 1400 °C and strain rate of 1.3 × 10⁻⁴ s⁻¹. The decreased strain hardening and increased ductility in the SiO₂ doped specimens are due to the segregation of amorphous glassy phase to the grain boundaries, thus hindering grain growth and facilitating grain boundary sliding, which is the primary mechanism of deformation in fine grained materials at high temperatures.     

Effect of inorganic nanoparticles on mechanical property, fracture toughness and toughening mechanism of two epoxy systems

We investigated the effect of silica nanoparticles on the mechanical property and fracture toughness of two epoxy systems cured by Jeffamine D230 (denoted J230) and 4,4′-diaminodiphenyl sulfone (denoted DDS), respectively. Toughening mechanisms were identified by a tailor-loaded compact tension method which quantitatively recorded the deformation of a damage zone in the vicinity of a sub-critically propagated sharp crack tip. 20 wt% silica nanoparticles' fraction provided 40% improvement in Young's modulus for both systems; it improved the toughness of J230-cured epoxy from 0.73 to 1.68 MPa m^1/2, and for the other system improved from 0.51 to 0.82 MPa m^1/2. The nanoparticles not only stiffen, strengthen and toughen epoxy, but reduce the effect of flaws on mechanical performance as well. In both systems, nanosilica particle deformation, internal cavitation and interface debonding were not found, different to previous reports. This could be due to the various hardeners used or different identification techniques employed. The toughening mechanisms of the J230-cured nanocomposite were attributed to the formation and development of a thin dilatation zone and nanovoids, both of which were induced, constrained and thwarted by the stress fields of the silica nanoparticles. Regarding 10 wt% silica-toughen epoxy cured by J230, a thicker and shorter dilatation zone was found, where neither nanoparticles nor nanovoids were observed. With regard to the DDS-cured system, much less dilatation and voids were found due to the hardener used, leading to moderately improved toughness.     

Comparison of fracture behavior of nylon 6 versus an amorphous polyamide toughened with maleated poly(ethylene-1-octene) elastomers

The fracture behavior of an amorphous polyamide (Zytel 330 from DuPont), a-PA, and nylon 6 toughened by maleated poly(ethylene-1-octene) elastomers are reported. The deformation mechanisms during fracture were verified by examining an arrested crack tip and the surrounding regions using transmission electron microscopy analysis. a-PA blends show higher levels of impact strength and lower ductile-brittle transition temperatures than nylon 6 blends. Fracture toughness, characterized by both linear elastic fracture mechanics techniques in terms of the critical strain energy release rate, G_IC, and the essential work of fracture methodology, i.e. the limiting specific fracture energy, u_o, and the dissipative energy density, u_d, using thick (6.35 mm) samples with sharp notches, depends on ligament length, rubber content, rubber particle size and test temperature. In general, a-PA blends show larger values of u_d than do nylon 6 blends while the opposite is seen for u_o. The amorphous polyamide shows a similar critical upper limit on rubber particle size, or interparticle distance, for toughening as the semi-crystalline nylon 6; thus, it is clear that the crystal morphology around the rubber particles must not be the dominant cause of this critical size scale. The deformation mechanisms involved include cavitation of rubber particles followed by some crazing and then massive shear yielding of the matrix.     

The effects of thermomechanical history and strain rate on antiplasticization of PVC

Antiplasticization is mechanically characterized by an increase in the polymer stiffness and/or yield strength upon the incorporation of a small amount of a low-molecular weight diluent. It is attributed to hindrance of the local β-relaxation motions of the polymer. Here, we have studied the effects of thermal treatment, plastic deformation, and strain rate on the antiplasticization of the yield stress of a 95 wt% poly(vinyl chloride)/5 wt% dioctyl phthalate (PVC/5 wt% DOP) compound. Two thermal treatments were applied to the materials - cooling to room temperature from above T_g by a quench or by a slow oven-cool anneal. When compressed at low to moderate strain rates, antiplasticization was observed in the annealed (physically aged) PVC/5 wt% DOP but not in the quenched (unaged) PVC/5 wt% DOP. Load-unload-reload compression cycles revealed that antiplasticization can be erased by plastic strain; the anomalously high yield stress of PVC/5 wt% DOP observed in the first load cycle softens to a value lower than that of the neat PVC in subsequent cycles. The results indicate that disordered, high free volume microstructural states, obtained either from thermal quenching or from plastic straining, liberate the beta motions of the PVC molecule which, in turn, erase antiplasticization of the yield stress. Earlier work on the rate-dependence of yield has demonstrated that beta motions must be stress-activated in order to yield neat PVC when deformed at high strain rates (>100/s). Hence, we have characterized the rate-dependence of the antiplasticization of the yield stress by testing the annealed materials in uniaxial compression over a wide range of strain rates (10⁻⁴/s-3000/s). Antiplasticization was observed in PVC/5 wt% DOP in the low strain rate regime where beta motions are free in neat PVC but hindered in PVC/5 wt% DOP; however, the antiplasticization (elevation of yield stress) gradually diminished with increasing strain rate.     

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 (ID_c) of the blends was. This was why the ID_c (0.15 μm) of the polypropylene (PP)/rubber blends was smaller than that (0.30 μm) of the nylon 66/rubber blends, and the ID_c of the nylon 66/rubber blends was smaller than that (0.60 μm) of the high density polyethylene (HDPE)/rubber blends.