Rubber toughening of poly(ether imide) by modification with poly(butylene terephthalate)

Rubber toughening of poly(ether imide) (PEI) has been elusive up to now due to the high processing temperature of PEI, which leads to degradation of the rubber. In this study, by profiting from the miscibility between PEI and poly(butylene terephthalate) (PBT), and the low T_g of PBT, we prepared a blend by melt extrusion with 20 wt% PBT in an attempt to render it toughenable by decreasing its T_g and processing temperature. The PEI-rich blend was subsequently mixed with maleic anhydride (0.9 wt%) grafted poly(ethylene-octene) copolymer (mPEO) up to 30 wt%. The decrease in T_g and processing temperature resulted in no observable degradation of the mPEO, and to the formation of a homogeneous morphology of rubber particles with a fine particle size, indicating that compatibilization was achieved. Upon rubber addition, stiffness decreased, while a very large toughness increase occurred with only 15% mPEO (impact strength more than 10-fold that of the PEI-PBT matrix). Upon observation of the fracture surface, the increase in impact strength was attributed partially to the cavitation and debonding of the rubber particles, and mostly to the deformation and yielding of the PEI-PBT matrix.     

Supertoughness and critical interparticle distance dependence in poly(butylene terephthalate) and poly(ethylene‐co‐glycidyl methacrylate) blends

Supertough poly(butylene terephthalate) (PBT)‐based blends were obtained by the melt blending of PBT with 0–30 wt % poly(ethylene‐co‐glycidyl methacrylate) (EGMA). The reaction between PBT and EGMA was detected by torque measurements. The particle size was almost constant with increasing EGMA content, and this indicated that compatibilization occurred. The minimum EGMA content for achieving supertoughness (i.e., an impact strength 16 times greater than that of PBT) was 20 wt %. The interparticle distance was the parameter controlling toughness in these PBT/EGMA blends. The dependence of the critical interparticle distance (τ_c) on the modulus of the dispersed phase appeared only at low τ_c values, and the primary dependence of τ_c on the ratio of the modulus of the matrix to the modulus of the rubbery dispersed phase was proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2236–2247, 2003     

Crystallization behavior and hydrophilicity of poly (vinylidene fluoride) (PVDF)/poly (styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) blends

Poly (styrene-co-acrylonitrile) (SAN) is a hydrophilic non-crystalline copolymer, which is initially used in this paper to improve the hydrophilicity of poly (vinylidene fluoride) (PVDF). Investigation of the crystallization behavior of PVDF/SAN blends showed that the samples presented only α phase regardless of SAN content as cooling from the melt. A double-melting phenomenon was related to the perfection or crystal size of PVDF crystals. As the SAN content is increasing, crystallization of PVDF was limited, leading to a decreased crystallinity and lamellar growth. Besides, the hydrophilicity of PVDF was improved by blending with SAN. The sample containing 70 wt.% SAN performed a similar surface property of the neat SAN owing to the besieging of the PVDF phase by SAN. Observed from the cross section of the blends, PVDF/SAN blends were partially miscible with less than 50 wt.% SAN addition. As the SAN content was more than 50 wt.%, the crystalline PVDF particles clearly dispersed in the amorphous matrix.     

Effect of reactive compatibilization on the properties of poly(butylene terephthalate)/acrylonitrile–ethylene–propylene–diene–styrene blends

Blends of poly(butylene terephthalate) (PBT) with 30 wt % acrylonitrile–ethylene–propylene–diene–styrene (AES) were prepared with methyl methacrylate (MMA)/glycidyl methacrylate (GMA)/ethyl acrylate (EA) terpolymers (MGEs) as compatibilizing agents. These acrylic terpolymers were miscible with the styrene–acrylonitrile (SAN) phase of AES, whereas the epoxide groups of GMA could react with the PBT end groups; this could lead to the formation of grafted copolymers (PBT‐g‐MGE) at the PBT/AES interface during the melt processing of the blends if at least a fraction of this interface was formed between the PBT and SAN phases. This study found evidence of the aforementioned interfacial structure through the effectiveness of the MGE terpolymers in promoting the compatibilization, as evaluated by dynamical mechanical analysis, through the increase in the viscosity of the blends, and through the reduction of the AES particle size dispersed in the PBT matrix. These effects became more intense with an increase in the overall concentration of GMA in the blends and with a reduction of the molecular weight of MGE. Another effect promoted by the compatibilization was a remarkable reduction of the brittle–ductile transition temperatures of the blends, which was correlated with the reduction of the AES particle size. However, this correlation between the brittle–ductile transition temperatures and particle size did not hold for the blend with the lowest AES particle size, which showed a high ductile–brittle transition temperature. These mechanical behaviors were examined on the basis of the current theory of the toughening of thermoplastics, which takes into account the importance of the rubber interparticle distance and the cavitation process of these particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1244–1259, 2005     

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002     

Mechanical and fracture behavior of polypropylene/poly(ethylene-co-vinyl alcohol) blends compatibilized with ionomer Na

In this work the deformation and fracture behavior of PP/EVOH blends compatibilized with ionomer Na⁺ at room and low temperature was studied. Uniaxial tensile tests on dumb-bell samples and fracture tests on single-edge notched bending (SENB) specimens were performed for 10 wt.% and 20 wt.% EVOH blends with different ionomer content at 23 °C and −20 °C. The incorporation of EVOH to PP led to less ductile materials in tension as judged by the lower values of the ultimate tensile strain displayed by all PP/EVOH blends in comparison to neat PP. In contrast, the ionomer Na⁺ addition partially counteracted this effect. The compatibilizing effect of ionomer Na⁺ was also evident in fracture results since higher values of the fracture parameter were obtained for the ternary blends. SEM observations also confirmed this effect. On the other hand, PP/EVOH blends exhibited different fracture behavior with test temperature. All blends showed “pseudo stable” behavior at room temperature characterized by apparently stable crack growth that could not be externally controlled. On the contrary, blends behaved as semi-brittle at −20 °C with some amount of stable crack growth preceding unstable brittle fracture. Finally, irrespectively of the temperature or the ionomer content all PP/EVOH blends exhibited more ductile fracture behavior with a higher tendency to stable crack propagation than neat polypropylene.     

Polymer toughening using residue of recycled windshields: PVB film as impact modifier

In this work, poly(vinyl butyral) (PVB) film originated from the mechanical separation of windshields was tested as an impact modifier of Polyamide-6 (PA-6). The changes undergone by PVB film during the recycling process and the blend manufacturing were evaluated by thermal analyses, infrared spectroscopy and loss on ignition. Blends of PA-6/original PVB film and PA-6/recovered PVB film were obtained in concentrations ranging from 90/10 to 60/40. The mechanical properties of the blends were investigated and explained in light of the blends morphologies, which in turns were correlated to the changes undergone by the PVB film during the recycling process. The original film presented a plasticizer content of 33 wt.%, which decreased to as low as 20 wt.% after the recycling and blend preparation processes. The PA-6/PVB film blends presented lower values of tensile strength and Young’s modulus than Polyamide-6, but all blends presented a dramatic increase in their toughness, with a special feature for the 40 wt.% blend, which resulted in a super toughened material (impact strength exceeding 500 J/m). Similar results were obtained with recovered PVB film and super tough blends were also obtained. The use of recovered PVB resulted in a smaller improvement of the impact strength due to the loss of plasticizer undergone during the recycling process. The morphological observations showed that if the interparticle distance is smaller than around 0.2 μm (critical value), the notched Izod impact strength values increase considerably and the fracture surface of blends exhibit characteristics of tough failure.     

相容剂对PP/POE共混体系脆韧转变行为的影响

采用熔融挤出法制备了不同相容剂含量的PP/POE共混体系,测试了不同体系的脆韧转变温度、热性能和力学性能.结果表明,乙烯-丙烯多嵌段共聚物相容剂的加入降低了PP/POE共混物的脆韧转变温度,提高了共混物的韧性.AFM和STEM照片显示相容剂的加入减小了橡胶分散相的临界粒子间距,PP和POE在两相界面结合处相互扩散或渗透,实现了POE弹性体在PP树脂中合适的尺度分布以及良好的形态分散.当相容剂含量达到10％时,POE分散相尺寸细小均匀,分散相粒子粒径为0.54μm,粒子间距为0.1 μm,PP结晶链段更多地插入到弹性体内部,弹性体POE分散相形成明显的“硬核-软壳”结构.DSC曲线中结晶峰和熔融峰的变化说明适量的相容剂对于材料结晶度的提高具有一定的促进作用.力学性能测试结果可以看出相容剂的加入在提高材料韧性,降低其脆韧转变温度的同时也保持了材料的刚性性能.     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.     

碳酸钙粒子增韧高密度聚乙烯的脆韧转变-Wu氏增韧理论聚合物共混物脆韧转变判据的适用条件

采用不同尺寸的碳酸钙粒子增韧高密度聚乙烯,研究了不同温度下共混体系的临界粒子间距与碳酸钙粒子尺寸和含量之间的关系,确定了温度是Wu氏增韧理论临界粒子间判据适用性的重要影响因素。 结果表明,在17 ℃下,临界粒子间距与碳酸钙粒子的尺寸和含量无关,该条件下Wu氏增韧理论临界粒子间距判据是适用的;而随着温度的升高,发现临界粒子间距依赖于碳酸钙粒子的尺寸,表明高温条件下,Wu氏增韧理论临界粒子间距判据不再适用。     

Compatibilization level effects on the structure and mechanical properties of rubber‐modified polyamide‐6/clay nanocomposites

Exfoliated polyamide‐6 (PA6)/organically modified montmorillonite clay (OMMT) nanocomposites (PNs) were modified with partially maleinized styrene–ethylene/butadiene–styrene triblock copolymers (SEBS) at three maleinization levels in an attempt to link in these materials high toughness with appropriate small‐strain and fracture tensile properties. OMMT stayed only in the PA6 matrix, and no preferential location in the matrix/rubber interphase was observed. The increased dispersed phase size upon the addition of OMMT was attributed to interactions between maleic anhydride (MA) functionalized SEBS and the surfactant of OMMT. The rubber particle size generally decreased when the MA content of SEBS increased, and this indicated compatibilization. The subsequent good adhesion led to tough nanocomposites across a wide range of both strain rates and fracture modes. As the critical interparticle distance (τ_c) decreased with the MA content, and the other parameters that could influence the surface‐to‐surface mean interparticle distance did not change, it is proposed that in these PNs higher adhesion leads to a smaller τ_c value. Finally, the presence in the matrix of a nanostructured clay makes the rubber content necessary for the toughness jump to increase and τ_c to decrease. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3611–3620, 2005     

Fractionated crystallization of compatibilized LDPE/PA6 blends

The paper presents differential scanning calorimetry and electron microscopy of the fractionated crystallization and polydispersity of the dispersed PA6 phase in compatibilized LDPE/PA6 75/25 w/w blends. The compatibilizers used were (i) an acrylic acid functionalized polyethylene, Escor 5001 (EAA); (ii) an ethylene-glycidylmethacrylate copolymer, Lotader GMA AX8840 (EGMA); (iii) a polystyrene-poly(ethylene-butylene)-polystyrene triblock copolymer comprising 2 wt.% maleic anhydride grafts, Kraton FG 1901X (SEBS-g-MA). The compatibilizer SEBS-g-MA has the strongest reduction effect upon the size of PA-6 droplets. Its implementation provides the best fractionated crystallization. The fractionated crystallization has not been observed for the blend compatibilized with EGMA. The results show that the degree of compatibilization could be evaluated qualitatively by the progress of the fractionated crystallization. So, the three compatibilizers could be rated according to their effectiveness as follows: SEBS-g-MA > EAA > EGMA. The self-nucleation experiments have demonstrated that the lack of active nuclei in the finely dispersed PA6 droplets is the determining factor for the fractionated crystallization at high supercooling, and not the considered absolute particle size. The measurement of the Vickers microhardness of the compatibilized blends confirms that the compatibilizing activity of SEBS-g-MA and EAA is stronger than that of EGMA.     

Sub-micrometer thermoplastic vulcanizates obtained by reaction-induced phase separation of miscible mixtures of poly(ethylene) and alkyl methacrylates

Sub-micrometer (μm) thermoplastic vulcanizates (TPVs) with cross-linked rubber particles with sizes ranging from 70 to 400 nm were prepared by reaction-induced phase separation (RIPS) of initially miscible blends of poly(ethylene) (PE), lauryl methacrylate (LMA) and divinylbenzene (DVB). Cross-linking under static conditions led to (partial) connectivity of the rubber particles via chemical bridging of grafted PE chains. Dynamic preparation conditions caused the connected structure to break-up, which led to a significant enhancement of the mechanical properties and the melt processability. The addition of 25-80 wt% extender oil resulted in a reduced complex viscosity and yield stress in the melt, without deteriorating the mechanical properties. The relatively good elastic recovery and excellent ultimate properties of these high hardness TPVs may be explained by the sub-μm rubber dispersions.     

Poly(ethylene-co-vinyl alcohol) and poly(methyl methacrylate) blends: Phase behavior and morphology

In this work blends of poly(ethylene-co-vinyl alcohol) (EVOH) with different ethylene contents (27, 32, 38 and 44 mol%) and poly(methyl methacrylate) (PMMA) were prepared by mechanical mixing in the melted state. The miscibility and melting behavior as a function of blend composition and the ethylene content in EVOH copolymers were investigated by means of differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The morphology of the cryofractured surfaces was examined by scanning electron microscopy (SEM). DSC and DMTA data show that EVOH/PMMA blends are immiscible, independent of EVOH and blend composition. The SEM analysis in agreement with DMTA analysis indicates that the morphology of phases depends on the blend composition, with phase inversion occurring as the concentration of one or other polymer component increases. However, the copolymer composition apparently does not affect the domain size distribution for blends containing 20 wt% of EVOH or 20 wt% of PMMA. A better phase adhesion is observed mainly for blends with 50 wt% of each polymer component.     

Crystallization behavior and hydrophilicity of poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA)/poly(styrene-<Emphasis Type="Italic">co</Emphasis>-acrylonitrile) (SAN) ternary blends

Compatibilization of the partially miscible poly(vinylidene fluoride) (PVDF)/poly(styrene-co-acrylonitrile) (SAN) pair by a third homopolymer, i.e., poly(methyl methacrylate) (PMMA), was investigated in relation to cross section morphology, crystallization behaviors and hydrophilicity of the polyblends. Scanning electron microscopy showed a more regular and homogeneous morphology when more than 15 wt.% PMMA was incorporated. The samples presented only α phase regardless of PMMA content in the blend. As the PMMA content increased in the blends, the interactions between each component were enhanced, and the crystallization of PVDF was limited, leading to a decreasing of the crystallinity and the crystallite thickness. Besides, the hydrophilicity of PVDF was further improved by PMMA addition. The sample containing 15 wt.% PMMA showed a more hydrophilic property due to the more polar part of surface tension induced by PMMA addition. Observed from the cross section of the blends, the miscibility of partially miscible PVDF/SAN blends were efficiently improved by PMMA incorporation.     

Effect of nanoscale fully vulcanized acrylic rubber powders on crystallization of poly(butylene terephthalate): Isothermal crystallization

Poly(butylene terephthalate) (PBT) was blended with nanoscale fully vulcanized acrylic rubber (FVAR) powders in a twin extruder, and the FVAR powders were dispersed well in PBT from scanning electron microscopy (SEM) and transmission electron microscope (TEM) investigation. The isothermal crystallization kinetics of PBT/FVAR blends were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. Equilibrium melting temperature was estimated by the nonlinear Hoffman-Weeks relation. The active energy (ΔE) and nucleation parameters (K_g) increased with the addition of FVAR, suggesting that FVAR particles hindered the crystallization; however more content FVAR had a lower ΔE and K_g because FVAR powders acted as heterogeneous nuclei in the nucleation of crystallization and facilitated the crystallization of PBT. The crystallization ability followed the order: PBT > PBT/FVAR6 > PBT/FVAR3 > PBT/FVAR1 when undercooling was considered.     

Properties of fluoroelastomer/semicrystalline perfluoropolymer nano-blends

Properties of blends of semicrystalline perfluoropolymers in fluoroelastomers strongly depend on the size of the dispersed phase and are at the best when dispersed phase dimension is well below 0.1 μm, i.e. in the nano-scale region. This fine dispersion is obtained with an innovative mixing technology based on microemulsion polymerization. Further increase of properties can be obtained by generating chemical links between fluoroelastomer and semicrystalline fluoropolymer. Nano-blends combine the performing properties of fluoroelastomers with those of semicrystalline perfluoropolymers. For example, these nano-blends have at the same time the sealing and mechanical properties of fluoroelastomers and the exceptional thermal and chemical resistance, low permeability and low friction coefficient of semicrystalline perfluoropolymers. In addition, as dispersed phase size is below visible light wavelength, finished items made with these nano-blends are optically transparent even when they contain as much as 40 wt.% of semicrystalline perfluoropolymer.     

Morphology and properties of isotactic polypropylene/poly(ethylene terephthalate) in situ microfibrillar reinforced blends: Influence of viscosity ratio

In situ microfibrillar reinforced blends based on blends of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET) were successfully prepared by a “slit extrusion-hot stretching-quenching” process. Four types of iPP with different apparent viscosity were utilized to investigate the effect of viscosity ratio on the morphology and mechanical properties of PET/iPP microfibrillar blend. The morphological observation shows that the viscosity ratio is closely associated to the size of dispersed phase droplets in the original blends, and accordingly greatly affects the microfibrillation of PET. Lower viscosity ratio is favorable to formation of smaller and more uniform dispersed phase particles, thus leading to finer microfibrils with narrower diameter distribution. Addition of a compatibilizer, poly propylene-grafted-glycidyl methacrylate (PP-g-GMA), can increase the viscosity ratio and decrease the interfacial tension between PET and iPP, which tends to decrease the size of PET phase in the unstretched blends. After stretched, the aspect ratio of PET microfibrils in the compatibilized blends is considerably reduced compared to the uncompatibilized ones. The lower viscosity ratio brought out higher mechanical properties of the microfibrillar blends. Compared to the uncompatibilized microfibrillar blends, the tensile, flexural strength and impact toughness of the compatibilized ones are all improved.     

环氧化三元乙丙橡胶增韧聚对苯二甲酸丁二酯的脆韧转变

环氧化的三元乙丙橡胶(eEPDM)与聚对苯二甲酸丁二酯(PBT)共混可以使PBT共混体的缺口冲击强度获得很大的提高.当eEPDM橡胶浓度为24wt%时,PBTeEPDM共混体的缺口冲击强度是纯PBT的12倍.随着eEPDM含量的增加,在室温下PBTeEPDM共混体出现了明显的脆韧转变,其脆韧转变的临界粒子间距为0.49μm.橡胶的加入及含量的增加使PBT体系的脆韧转变温度(TBD)向低温移动,且PBTuEPDM与PBTeEPDM共混体脆韧转变温度的差随橡胶含量的增加而逐渐增大.扫描电镜照片表明,在橡胶组成相同的情况下,PBT基体中分散的eEPDM粒子明显小于未环氧化的EPDM粒子.且eEPDM橡胶的粒子间距(ID)也明显地低于uEPDM橡胶粒子的ID,这导致PBTeEPDM共混体系在室温下出现脆韧转变.     

Confocal microscopy studies of shear‐induced coalescence in blends of poly(butyl methacrylate) and poly(2‐ethylhexyl methacrylate)

This article reports the results of confocal fluorescence microscopy studies of shear‐induced coalescence in binary blends of poly(2‐ethylhexyl methacrylate) (PEHMA; 90 wt %) and poly(butyl methacrylate) (PBMA; 10 wt %). We prepared the blends by casting a mixture of latex dispersions of the components onto a substrate and allowing the film to dry under ambient conditions. The initial morphology of the film was a dispersion of 120‐nm PBMA spheres in a continuous PEHMA matrix. One‐fifth of the PBMA particles were labeled with anthracene, the emission of which we observed with confocal microscopy. The blends were sheared in a parallel‐plate rheometer at 80 and 100 °C for 1 and 10 h. Careful image analysis allowed us to estimate the mean size of the dispersed phase and the width of the size distribution. The results were compared with the theoretical limits of Wu and Taylor. After 10 h of shearing, the mean particle size decreased and the particle distribution became narrower in comparison with the results obtained after 1 h of shearing. We explain this result by inferring that before the sample reached steady‐state morphology, its rate of coalescence was greater than the rate of particle breakup. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2317–2332, 2001