Preparation of polypropylene/ethylene‐propylene‐diene terpolymer/nitrile rubber ternary thermoplastics vulcanizates with good mechanical properties and oil resistance by core‐shell dynamic vulcanization

As the most successful commercialized thermoplastic vulcanizates (TPVs), polypropylene (PP)/ethylene propylene rubber (EPDM) TPVs exhibit poor oil resistance. In this work, we prepared PP/EPDM/butadiene acrylonitrile rubber (NBR) ternary TPVs with good oil resistance using core‐shell dynamic vulcanization. According to the theoretical analysis of the spreading coefficient and the transmission electron microscopy results, the rubber phases exhibited a special core‐shell structure, in which the cross‐linkedNBR‐core was encapsulated by the EPDM‐shell. The core‐shell structure effectively improved the interfacial compatibility between PP and NBR phase as the EPDM‐shell could avoid the direct contact of them, thus improving the mechanical properties of the TPVs. For example, the PP/EPDM/NBR (40/30/30) ternary TPV showed enhanced tensile strength of 12.57 MPa, compared with 10.71 MPa of PP/EPDM (40/60) TPV and 11.11 MPa of PP/NBR (40/60) TPV, respectively. Moreover, the oil resistance of the TPVs was also improved. Compared with PP/EPDM TPV, the change rates in mass, volume, tensile strength and elongation at break of PP/EPDM/NBR TPV after oil immersion decreased by 42.18%, 48.69%, 52.68% and 28.77%, respectively.     

Prediction models for the key mechanical properties of EPDM/PP blends as affected by processing parameters and their correlation with stress relaxation and phase morphologies

The optimum condition of processing parameters (mixing temperature, rotor speed, fill factor, and blend ratio) and prediction models for the best key mechanical properties of ethylene propylene diene terpolymer/polypropylene thermoplastic vulcanizates (EPDM/PP TPVs) was investigated by using the Taguchi's optimization technique and data analysis. The results reveal that all of the processing parameters affected significantly the mechanical properties of the EPDM/PP TPVs, but specifically the blend ratio contributed more than 90% in effect size on tensile strength and tension set. There were three main factors, the mixing temperature, the fill factor, and the blend ratio, influencing the elongation at break. Furthermore, the mathematic models were effective and reliable in predicting the properties of TPVs. The correlation of mechanical properties, stress relaxation, and phase morphologies of the TPVs prepared from the predicted models was also investigated. It can be summarized that the morphological structure and stress relaxation of the TPVs were strongly governed by the EPDM content in the blend ratio. That is, the higher the EPDM content, the better phase morphology having smaller size of the vulcanized EPDM particles distributed in the PP matrix and the higher rate of stress relaxation. Moreover, these two properties were then principally pushing the mechanical characteristics of the EPDM/PP TPVs. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and flammability of EPDM/PP/Mg(OH)2 dynamic vulcanizates

Magnesium hydroxide (MH) flame retardant dynamic vulcanized ethylene‐propylene‐diene terpolymer (EPDM)/polypropylene (PP) thermoplastic vulcanizates (TPVs) were prepared by a twin‐screw extruder. Influences of MH on their morphology, mechanical properties, flammability, and crystallization behavior have been investigated. Static tensile measurements exhibited that TPVs have higher mechanical properties than un‐vulcanized EPDM/PP/MH blends (UVBs). Scanning electron microscopy (SEM) studies showed that the formation of the larger‐size “micro‐encapsulated structure” where the MH aggregates were covered with a cross‐linked rubber phase improved the interaction between MH and polymer matrix. Results of limiting oxygen index (LOI) and microscale combustion calorimetry (MCC) confirmed that TPVs had superior fire‐resistant properties to UVBs. SEM images showed that more uniform and compact charred layers were generated in TPVs. The differential scanning calorimetry (DSC) results indicated that the crystallization behavior of the flame retardant TPVs changed marginally with increase in MH content. Copyright © 2009 John Wiley & Sons, Ltd.     

Mechanical and Rheological Behavior of Unvulcanized and Dynamically Vulcanized i-PP/EPDM Blends

The mechanical and rheological behavior of dynamically vulcanized PP/EPDM blends is examined and compared with those of unvulcanized blends. The effect of blend ratio and dynamic vulcanization of EPDM rubber on tensile properties and flow are investigated. The mechanical properties of the blends are strongly influenced by the blend ratio. With the increasing of EPDM content the value of yield stress in a solid state decreases with the elastomer volume fractions less than 0.45 for the unvulcanized blends. For the dynamically vulcanized blends the interval of EPDM content, at which the yield peak is seen, is rather limited below 0.25 elastomer volume fractions. It is shown that dynamic vulcanization changes the deformational behavior of PP/EPDM blends. The rheological properties of dynamically vulcanized blends depending on the ratio of the components may be similar to the properties of polymer composites containing the highly disperse structuring filler. The distinction between the rheological behavior of unvulcanized and dynamically vulcanized blends is related to differences of their structures and viscoelastic characteristics of unvulcanized and vulcanized EPDM phase.     

The effects of reprocessing cycles on the structure and properties of isotactic polypropylene/cloisite 15A nanocomposites

The effects of reprocessing cycles on the structure and properties of isotactic polypropylene (PP)/Cloisite 15A (OMMT) (5 wt. %) nanocomposites was studied in presence of maleic anhydride-grafted-polypropylene (PP-g-MA) (20 wt. %) used as the compatibiliser to improve the clay dispersion in the polymer matrix. The various nanocomposite samples were prepared by direct melt intercalation in an internal mixer, and further they were subjected to 4 reprocessing cycles. For comparative purposes, the neat PP was also processed under the same conditions. The nanocomposite structure and the clay dispersion have been characterized by wide angle X-ray scattering (WAXS), transmission electron microscopy (TEM) and rheological measurements. Other characterization techniques such as Fourier transform infrared spectroscopy (FT-IR), tensile measurements, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) have also been used to evaluate the property changes induced by reprocessing. The study showed through XRD patterns that the repetitive reprocessing cycles modified the initial morphology of PP/OMMT nanocomposites by improving the formation of intercalated structure, especially after the fourth cycle. Further, the addition of PP-g-MA promoted the development of intercalated/exfoliated silicate layers in the PP matrix after the second cycle. These results are in agreement with TEM observations indicating an improved silicate dispersion in the polymer matrix with reprocessing cycles displaying a morphology with both intercalated/exfoliated structures. The initial storage modulus (G′) of the nanocomposites, which was highly improved in presence of PP-g-MA seems to be less affected by reprocessing cycles at very low frequencies exhibiting a quasi-plateau compared to pristine PP/OMMT and PP. In contrast, the complex viscosity was found to decrease for the whole samples indicating that the main effect of reprocessing was a decrease in the molecular weight. Moreover, the thermal and mechanical properties of the nanocomposites were significantly reduced after the first cycle; nevertheless they remained almost unchanged during recycling. No change in the chemical structure was observed in the FT-IR spectra for both the nanocomposites and neat PP samples after 4 cycles.     

Mechanical properties and morphological structures of short glass fiber reinforced PP/EPDM composite

The mechanical properties and crystal morphological structures of short glass fiber (SGF) reinforced dynamically photo-irradiated polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) composites were studied by mechanical tests, wide-angle X-ray diffraction (WAXD), optical microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analyzer (TGA). The mechanical properties of PP/EPDM composites, especially the tensile strength were greatly strengthened by dynamically photo-irradiation and the incorporation of SGF. The results from the WAXD, SEM, DSC, and TGA measurements reveal: (i) the formation of β-type crystal of PP in the PP/EPDM/SGF composite; (ii) the fiber length in dynamically photo-irradiated PP/EPDM/SGF composites are general longer than that in corresponding unirradiated samples. The size of EPDM phase in the photo-irradiated composites reduces obviously whereas the droplet number increases; (iii) photo-irradiation improves the interface adhesion between SGF and polymer matrix; (iv) the melting and crystallization temperatures of the photo-irradiated composites are not affected greatly by increasing the SGF content; (v) the thermal analysis results show that the incorporation of SGF into PP/EPDM plays an important role for increasing its thermal stability.     

Rheology and phase structure of PP/EPDM/SiO2 ternary composites

In this article, the rheological properties of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM)/silicon dioxide (SiO₂) ternary composites were systematically investigated. Two kinds of nano-SiO₂ particles (with hydrophobic (denoted as A-SiO₂) or hydrophilic (denoted as B-SiO₂)) as well as two processing methods (one-step or two-step) were first employed to prepare PP/EPDM/SiO₂ ternary composites. Then the deep mixing and morphology evolution of polymer composite with mixing time were assessed by rheological method, on the focus of formation of filler-network, and compared with scanning electron microscopy (SEM) observations. Linear viscoelastic behavior was observed for PP/EPDM and PP/SiO₂ binary system, showing no evidence of the formation of filler-network structure. However, a solid-like rheological behavior, which was attributed to the formation of the filler-network structure as confirmed by SEM observation, could be observed in some PP/EPDM/SiO₂ ternary systems, depending on the SiO₂ surface property, processing method and EPDM content. It seemed that SiO₂ with hydrophilic surface was necessary for the formation of filler-network in PP/EPDM/SiO₂ ternary system. Besides, two-step processing method made the solid-like behavior occurred at an earlier stage compared with that of a one-step processing method, also, the higher elastomer content facilitated the formation of the filler-network structure. The results were in good agreement with those reported in our previous publications [Yang H, Zhang Q, Guo M, Wang C, Du R, Fu Q. Polymer 2006;47:2106] [Yang H, Zhang X, Qu C, Li B, Zhang L, Zhang Q, et al. Polymer 2007;48:860].     

Dynamically Photocrosslinking of Polypropylene／EPDM Blends as a Thermoplastic Elastomer

The mechanical properties and the crystal morphological structures of the dynamically photocrosslinked polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) blends have been studied by means of mechanical tests, wide-angle X-ray diffraction(WAXD), and differential scanning calorimetry(DSC). The dynamically photocrosslinking of the PP/EPDM blends can improve the mechanical properties considerably, especially the notched Izod impact strength at low temperatures. The data obtained from the mechanical tests show that the notched Izod impact strength of the dynamically photocrosslinked sample with 30% EPDM at -20℃ is about six times that of the uncrosslinked sample with the same EPDM component. The results from the gel content, the results of WAXD, and the DSC measurements reveal the enhanced mechanism of the impact strength for the dynamically photocrosslinked PP/EPDM blends as follows: (1) There exists the crosslinking of the EPDM phase in the photocrosslinked PP/EPDM blends ; (2) The β-type crystal structureof PP is formed and the content of α-type crystal decreases with increasing the EPDM component; (3) The graft copolymer of PP-g-EPDM is formed at the interface between the PP and EPDM components. All the above changes of the crystal morphological structures are favorable for increasing the compatibility and enhancing the toughness of the PP/EPDM blends at low temperatures.     

Effects of cooling rates on crystallization behavior and melting characteristics of isotactic polypropylene as neat and in the TPVs EPDM/PP and EOC/PP

Non-isothermal crystallization behavior and melting characteristics of polypropylene (PP) in EPDM/PP and EOC/PP TPVs were studied at various cooling rates using differential scanning calorimetry (DSC). The results revealed that the crystallization of PP in the TPVs occurs at a lower degree of undercooling, relative to neat PP, with smaller size PP crystals. The vulcanized EPDM and EOC particles could accelerate the crystallization of the PP phase either by providing nucleation or by promoting interfacial crystallization. The crystallization exotherm and melting endotherm peaks of the TPVs were broad, and they shifted towards lower temperatures as the cooling rate was increased. The analysis of non-isothermal crystallization kinetics indicates that the crystallization of the PP in the TPVs is heterogeneous nucleation, with two or three-dimensional growth during primary and secondary crystallization. Furthermore, the vulcanized EPDM and EOC particles promote the initial crystallization activation energy of the PP in TPVs to exceed that of the neat PP. The developed mathematical models show an approximately power-law dependence on the cooling rate for the crystallization behavior and the melting characteristics of PP in the TPVs.     

Study on Dynamic Vulcanized EPDM/PP Thermoplastic Elastomer

Based upon the THE,HAAK RHEOCORD 90 and Wx-ray observation,a study was made on the structure and property of ethylene-propylene-ethlidene norborene (EPDM)/polyprolene (PP) blending systems ,and the experimental results were fully explained. (1) The effect of Mooney viscosity (ML)of EPDM、 melt flow rate(MFR) of peroxide(DCP) and mixing steps on mechanical properties of EPDM/PP blends was studied. The results showed that the mechanical and process properties of EPDM?PP thermoplastic elastomers were better using EPDM with the ML of 60 and PP with MFR of 7.5g/10min as matrix,DCP with the content of 1.2 per cent with the help of twostep curing process at the temperature of 170-175 ℃.     

PP/EPDM/CaCO3三元复合材料的相结构及力学性能研究

采用以化学键合方式在CaCO3表面包覆上聚丙烯蜡和将改性后的CaCO3先与EPDM复合、再与PP复合的工艺,制备PP/EPDM/CaCO3三元复合材料,以期在PP基体材料中得到EPDM包裹CaCO3的相结构.通过测量三元复合体系中各组分的表面张力,计算各可能组分对之间的界面张力和黏结功,分析三元复合体系中可能的相结构.热力学计算结果表明,三元复合体系中既存在以EPDM为壳、CaCO3为核的"核壳结构",又存在CaCO3与EPDM各自独立分散在PP基体中的结构.电镜照片进一步揭示,在PP/EPDM/改性CaCO3三元复合体系与PP/EPDM/未改性CaCO3三元复合体系中,这两种相结构的比例是不同的,在前者中以核壳结构为主.CaCO3表面性质的不同是产生这一差别的原因.由于这一结构差别的存在,PP/EPDM/改性CaCO3三元复合体系比PP/EPDM/未改性CaCO3三元复合体系具有更好的力学性能.当EPDM用量为8 phr、改性CaCO3用量为15 phr时,三元复合体系的冲击强度达14.25 kJ/m2,是纯PP的3.17倍.     

Effect of β-phase on the fracture behavior of dynamically vulcanized PP/EPDM blends studied by the essential work of fracture approach

The effect of β phase polypropylene (PP), induced by β-nucleating agent (β-NA), on the fracture behavior in dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend was studied. Differential Scanning Calorimetry (DSC) and Wide-angle X-ray diffraction (WAXD) were employed to study the melting behavior and crystalline structures, and the results indicated that the β-NA induced β phase of PP effectively in TPVs. With the increasing dosage of the β-NA incorporated in, the content of β phase increased while the total crystallinity of the blend kept constant. The fracture behavior of the TPVs with different β phase content was studied with double edge notched tensile loaded specimens (DENT) using the essential work of fracture (EWF) approach. The specific essential work of fracture (w_e) increased with the increasing of β phase content, indicating that the presence of β phase could effectively enhance the fracture toughness of TPVs.     

Synergistic effects of cerium phosphate and intumescent flame retardant on EPDM/PP composites

An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd.     

COMPATIBILIZERS FOR LOW DENSITY POLYETHYLENE/POLYPROPYLENE BLENDS

The role of polyolefin elastomers as compatibilizers in Low Density Polyethylene/Polypropylene (LDPE/PP) blends, in the presence of di-cumyl peroxide (DCP) has been studied. Mixtures of 90/10 LDPE/PP ratio, were prepared in a Brabender plasticorder and tested for their mechanical properties and calorimetric response. Then the elastomers ethylene-propylene-diene copolymer (EPDM) and polybutadiene (BR) were added, alone or together with 0.2% DCP at concentrations up to 2%. The mixing torque and gel content of the above products were recorded as a function of the blend consistency. Also, the mechanical properties of specimens were measured as an additional evidence to explore the capabilities of these additives to promote compatibility of the blend components. It was found that EPDM and BR can be easily incorporated into polyolefin blends and appear suitable as potential compatibilizers for those materials, probably acting within the PP phase. Both elastomers result in an increase of strength and modulus, the BR having more enhanced effect. The latter gives low elongation, which allows its use in applications where high tensile properties are desired and flexural behavior is not critical.     

Shape memory properties of dynamically vulcanized poly(lactic acid)/nitrile butadiene rubber (PLA/NBR) thermoplastic vulcanizates: The effect of ACN content in NBR

Morphology structure and interfacial interaction are crucial factors for shape memory thermoplastic vulcanizates. In this study, shape memory thermoplastic vulcanizates based on poly(lactic acid) (PLA) and nitrile butadiene rubber (NBR) were prepared through dynamic vulcanization. The influence of acrylonitrile (ACN) content on the morphology, compatibility, shape memory property, and mechanical property was investigated. A co‐continuous structure was observed. The interfacial compatibilization between PLA and NBR phases occurred, resulting in a significantly improved interface adhesion and interfacial interaction, which was confirmed by Fourier transform infrared spectroscopy. With such a novel structure, the PLA/NBR TPVs owned an excellent shape memory property and further improved with increasing ACN content of NBR, which could be explained that the cross‐linked continuous NBR phase provided a stronger recovery driving force. In the meantime, tensile strength and elongation at break of TPVs increased with increase in ACN content. It is concluded that the preparation of dynamically vulcanized thermoplastic vulcanizate with co‐continuous structure and strong interfacial adhesion is beneficial to obtain outstanding shape memory effect.     

Novel fluorosilicone thermoplastic vulcanizates prepared via core‐shell dynamic vulcanization: Effect of fluororubber/silicone rubber ratio on morphology,crystallization behavior,and mechanical properties

Recently, we have reported a novel core‐shell dynamic vulcanization method to prepare poly(vinylidene fluoride) (PVDF)/fluororubber (FKM)/silicone rubber (SR) thermoplastic vulcanizates (TPVs) with cross‐linked rubber core‐shell particles. However, the shell thickness on the properties has not been studied in detail. Herein, these PVDF‐based TPVs different FKM‐shell thickness were prepared by changing FKM/SR ratios. The effect of FKM‐shell/SR‐core ratio on morphology, crystallization, and mechanical properties of the ternary TPVs was studied. The results showed that the FKM shell had more positive effect on interfacial‐induced crystallization behavior than the SR core due to its better compatibility with PVDF. When the FKM/SR ratio was <1, FKM was not enough to encapsulate SR completely, which resulted in the formation of imperfect core‐shell structure. However, when the FKM/SR ratio was >1, perfect core‐shell structure was formed. Therefore, the mechanical properties improved with increasing FKM content; especially, a remarkable improvement was observed when FKM/SR ratio was >1. This study could provide more information for the design of TPVs with core‐shell structure.     

Study on mechanical properties and phase morphology of polypropylene/polyolefin elastomer/magnesium hydroxide ternary composites

In this work, elastomer‐toughened polypropylene (PP)/magnesium hydroxide (MH) composites with ethylene–octene copolymer (POE) were prepared in a twin‐screw extruder and then injection‐molded. The structure, mechanical properties, phase morphology, and rheological behaviors of PP/POE/MH ternary composites were studied. The mechanical properties and fracture behaviors of PP/POE/MH ternary composites are strongly influenced by the incorporation of POE copolymer. The addition of POE causes a significant improvement in the impact strength of the composites, from 3.6 kJ/m² in untoughened composites to 47.4 kJ/m² in PP composites containing 30 phr POE. This indicates that POE is very effective in converting brittle PP composites into tough composites. Conversely, the tensile strength and the Young's modulus of the composites decrease with respect to the PP composites, as the weight fraction of POE is increased to 40 phr. Scanning electron microscopy (SEM) study shows a two‐phase morphology where POE, as droplets, is dispersed finely and uniformly in the PP matrix. The rheological behaviors show that the interfacial interaction in the composites is enhanced with increase in POE content. Interparticle interactions give rise to the formation of interparticle network. Copyright © 2009 John Wiley & Sons, Ltd.     

Recent Developments for EPDM-Based Thermoplastic Vulcanisates

An overview will be given on thermoplastic vulcanisates (TPVs). Like other thermoplastic elastomers, TPVs combine the elastic and mechanical properties of thermoset cross-linked rubbers with the melt processability of thermoplastics. Emphasis will be on general-purpose TPVs, based on resol-cross-linked EPDM/PP/oil blends. The following recent scientific developments will be discussed in detail: resol cross-linking chemistry, extruder dynamic vulcanisation, TPV morphology, oil distribution, TPV elasticity model and TPV rheology. A series of scientific questions and technological problems, which are challenging future TPV developments, will be put forward at the end.     

PP/EPDM共混物热氧稳定性研究

通过热氧加速老化的方法研究了不同的EPDM含量和抗氧剂对聚丙烯和三元乙丙橡胶共混物(PP/EPDM)热氧稳定性的影响.通过对老化前后试样的力学性能变化分析,热失重(TG)分析和扫描电镜(SEM)分析,结果表明:在热氧加速老化的初期,PP/EPDM共混物的拉伸强度随着时间的增长呈逐渐上升的趋势;在老化中期,共混物的拉伸强度变化不大;在老化后期,共混物的拉伸强度逐渐下降.在整个老化过程中,断裂伸长率都呈逐渐下降的趋势.而随着EPDM含量的增加,相应共混物的拉伸强度和断裂伸长率的下降减缓;相应共混物的分解温度得到较大的提高;抗氧剂的加入,能进一步提高共混物的热氧稳定性.     

Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites

Microscopic, mechanical, rheological and thermal tests were carried out in order to determine the recycling behaviour of PP/vegetal fibre composites. Different composites using hemp and sisal were characterized. All results were compared with PP-g-MA/hemp composites and PP/glass fibre composites.The results prove that mechanical properties are well conserved with the reprocessing of PP/vegetal fibre composites but that there is poor adhesion between the fibres and PP without any treatment. The addition of PP-g-MA shows an improvement of the bonding evidenced by MEB pictures. Vegetal fibres induce an increase in the percentage of crystallinity χ_c and in the crystallization temperature T_c which can be explained by the nucleating ability of the fibres improving crystallization of PP. The Newtonian viscosity η₀ decreases with cycles, indicating a decrease in molecular weight and chain scissions induced by reprocessing. The decrease of fibre length with reprocessing could be another reason for viscosity decrease.