Effect of process parameters on the adhesion strength in two‐component injection molding of thermoset rubbers and thermoplastics

Recently, a novel two‐component injection molding process has been developed for combining thermoplastics with thermoset rubbers. This process is of interest for example when thermoplastic parts include seals which are usually produced out of thermoset rubber. The present study evaluates the influence of different process parameters on the bond strength by means of a half factorial experimental design. The considered process parameters are the mold temperature at the interface, the injection temperature, the injection speed, the holding pressure, and the initial roughness of the thermoplastic part at the later interface. The study indicates a large influence of the mold temperature at the interface. Furthermore, the holding pressure only affects the adhesion strength when it is set too low or when the holding time is too short. The other process parameters have no significant effect on the adhesion strength. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46495.     

Wetting measurements as a tool to predict the thermoplastic/thermoset rubber compatibility in two‐component injection molding

Recently a novel two‐component injection molding process has been developed combining thermoplastics with thermoset rubbers. Since the adhesion strength between the two materials strongly depends on the combination of a specific thermoplastic and a thermoset rubber, there is a need to predict their compatibility, defined as the formation of a strong interface. In this study, the wetting behavior of molten thermoplastics on rubber substrates is used to predict their compatibility since wetting is an essential step in the formation of a strong interface. Contact angle measurements at high temperatures showed that the wetting of polypropylene and polyethylene is the best in combination with ethylene propylene diene monomer rubber while nitrile rubber is best wetted by polycarbonate. The subsequent two‐component injection molding tests confirm that it is possible to combine these materials. Material combinations with a poor wetting behavior on the other hand are not suitable for two‐component injection molding. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46046.     

Mechanical properties and morphological structures relationship of blends based on sulfated EPDM ionomer and polypropylene

The mechanical properties and morphological structures of blends based on Zn²⁺ neutralized low degree sulfated ethylene propylene diene monomer rubber (Zn–SEPDM) ionomer and polypropylene (PP) were studied. It was found that Zn²⁺ neutralized low degree sulfated EPDM ionomer and PP blends, which are new thermoplastic elastomeric materials, have better mechanical properties than those of PP/EPDM blend. Theoretical analysis of tensile data suggests that there is an increase of the extent of interaction between PP and EPDM in the presence of a low degree of Zn²⁺, which is also an indicator of better interfacial adhesion between PP and Zn–SEPDM than that between PP and EPDM. SEM results proved that the finer dispersed phase sizes and the shorter interparticle distances are the main reasons for the improved mechanical properties of the PP/EPDM blend. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1504–1510, 2004     

Effect of contact time and temperature on adhesion between components of rubber-polyethylene thermoplastic composites

—The effect of contact time and temperature on the adhesion between rubber and polyethylene has been studied. The degree of adhesion between natural rubber (NR) and polyethylene (PE) was varied by using physical (EPDM) and chemical interaction promoters (ENR/PE_m). It was observed that the peel strength increases with an increase in time of contact at a particular temperature. The adhesion strength varies with the square root of the contact time for all the systems with the exception of NR/PE/DCP at 75 and 100°C, EPDM/PE at 100°C, and NR/ENR/PE_m/PE at 100°C. With an increase in temperature, however, only EPDM-containing systems show higher values of adhesion between components. EPDM enhances the strength of the interface of the NR/PE joint, especially at longer contact times and higher temperatures. However, the chemical modifier is active only when the joining temperature is 150°C. On mastication of NR up to 15 min, the adhesion between natural rubber and polyethylene increases. The tack strength of NR-PE composites is increased with the introduction of physical and chemical modifiers.     

Adhesion between individual components and mechanical properties of natural rubber-polypropylene thermoplastic elastomeric blends

Adhesion between individual components and the mechanical properties of natural rubber (NR)-polypropylene (PP) thermoplastic elastomeric blends with reference to adhesion have been studied. The adhesion strength between the component phases was varied by incorporating a third component, namely ethylene propylene diene rubber (EPDM) or chlorinated polyethylene (CPE), and their effects on the mechanical properties were also studied. It was observed that the level of adhesion between NR and PP is improved by incorporating 20 parts of EPDM or CPE in NR. The mechanical properties of the blends are also improved for a particular composition. The enhancement in the strength properties and modulus of an NR:X:PP (where X is the third component) (70:10:30 or 70:20:30) blend is apparent when a correction due to the hard-phase contribution of the blend is made by taking the ratio of the strength of the composite to the strength of the hard phase or modulus of the blends. When the three-component blends were compared with a 90:30 blend of NR-PP, the role of adhesion played by EPDM or CPE in improving the strength and modulus could be demonstrated. In fact, there is a direct qualitative relationship between the adhesion and the mechanical properties in such composites. The stronger the adhesion, the greater the tensile strength and modulus. The higher adhesion strength is further reflected from the morphology of various blends. Separation of the phases during swelling and subsequent drying is restricted in the systems exhibiting higher adhesion strength between the components.     

Effect of dynamic crosslinking on impact strength and other mechanical properties of polypropylene/ethylene‐propylene‐diene rubber blends

The deformation and fracture behavior of several dynamic vulcanizate blends of isotactic polypropylene with ethylene‐propylene‐diene rubber (EPDM) was examined and compared with those of uncrosslinked blends of PP/EPDM. These blends were prepared by melt mixing in an internal mixer at 190°C in a composition range of 10–40 wt % EPDM rubber. The variation in yield stress, the strength of fibrils of the craze, and the number density of the EPDM rubber domains (morphology fixation) that are dominant factors for enhancing interfacial adhesion and toughness in dynamic vulcanizate blends were evaluated. The ductility and toughness of these materials were explained in light of the composition between crack formation and the degree of plastic deformation through crazing and shear yielding. The physicomechanical properties including the hardness, yield stress, Young's modulus, percentage elongation, impact strength, flexural strength, and flexural modulus of dynamic vulcanized blends were found to be consistent and displayed higher values compared with uncrosslinked blends. The nucleation effect of the crosslinked particles and the decrease of crystallinity of the EPDM rubber were also considered to contribute to the improvement in the impact strength. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2089–2103, 2000     

Evaluation of the role of devulcanized rubber on the thermomechanical properties of expanded ethylene-propylene diene monomers composites

Various amounts of both devulcanized (DR) and non-devulcanized (NDR) recycled rubber were melt compounded with a virgin ethylene-propylene diene monomer (EPDM) rubber. The resulting compounds were then expanded by using azodicarbonamide. The role played by the presence of DR or NDR on the thermomechanical properties of the obtained materials was evaluated. Electron scanning microscope micrographs highlighted that DR particles were better encapsulated within the EPDM matrix with respect to the corresponding NDR ones. Moreover, a better interfacial adhesion was observed with DR, probably due the re-vulcanization process in which the free crosslinking sites that typically characterize DR could form linkages with the EPDM matrix. Tensile impact behavior of expanded EPDM/recycled rubber blends highlighted a strong improvement of the normalized total absorbed energy, of the normalized impact strength and of the elongation at break with respect to the neat expanded EPDM for all the investigated compositions, and especially with a DR content of 20 wt%. The preparation of expanded EPDM containing considerable amounts of devulcanized rubber was, therefore, demonstrated to be a practical route to reduce the costs and improve the properties and the environmental sustainability of rubber products.     

Experimental and statistical study of the effects of material properties,curing agents,and process variables on the production of thermoplastic vulcanizates

A comprehensive experimental study together with statistical analysis was performed to identify the optimal process conditions, materials selection, and curing system for the production of thermoplastic vulcanizates (TPVs) based on EPDM rubber and polypropylene. Two types of curing systems were studied together with five different types of EPDM rubber. The TPV products were assessed according to elastic modulus and degree of swelling (indicators of crosslink density), ultimate tensile strength, ultimate elongation, tear strength, and compression set. A design of experiments method was applied to minimize the number of experiments and to obtain response surface and regression models for this complex and highly interactive system. From the modeling results, optimum values for the influential factors were obtained to achieve the target end product properties. It was found that a phenolic resin‐based curing system gave the best product properties and that the most influential factors were the rubber characteristics (ethylene content, ethylidene norbornene content, and molecular weight) and the polypropylene content in the formulation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of EPDM/SAN Dry Blends by Reactive Processing

Reactive blending of the rubber EPDM (a terpolymer consisting of ethylene, propylene and a diene) and the thermoplastic material SAN (a copolymer of styrene and acrylonitrile) is reinvestigated with special attention to EPDM/SAN blends with a 50/50 blend ratio. A resin cure system based on a low molecular weight phenol formaldehyde condensate, which primarily consists of dimethylolphenol and stannous dichloride, is used for compatibilization of EPDM and SAN, as well as for crosslinking of the EPDM phase. The amounts of phenolic resin and SnCl₂ · 2H₂O as well as the EPDM grade and the EPDM/SAN blend ratio are varied. The blends are characterized by stress‐strain measurements, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Unreacted EPDM, unreacted SAN and gel plus graft copolymer are quantitatively determined by fractionation of the blends with a binary solvent mixture which exhibits phase separation at room temperature. Blends prepared from EPDM grades that are amorphous and have a high molar mass exhibit high levels of gel and rather poor mechanical properties. With these blends, gel formation is favored over the formation of EPDM/SAN graft copolymers. Even with low levels of the resin cure system, the formation of gel cannot be avoided. It is therefore not possible to prepare graft copolymers without some gelling. Blends prepared from an EPDM grade with high crystallinity and a low Mooney viscosity exhibit substantially better mechanical properties than blends based on amorphous and higher viscosity EPDM grades. TEM and SEM micrographs reveal good dispersion of the two polymers, as well as good interfacial adhesion between the EPDM and the SAN phase. This electron microscopic evidence, in combination with low gel contents, supports the view that the tendency towards graft copolymer formation and gelling strongly depends on the EPDM grade used. Variation of the EPDM/SAN blend ratio between 5–90 wt.‐% results in blends which cover the product range from toughened thermoplastics to thermoplastic elastomers.

TEM of compatibilized EPDM/SAN blend.     

Interfacial adhesion and molecular diffusion in melt lamination of wood sawdust/ebonite NR and EPDM

Adhesion mechanisms and peel strengths of wood/ebonite NR‐EPDM laminates were investigated. Three different chemical coupling agents: namely; N‐(β aminoethyl)‐γ‐aminopropyl‐triethoxysilane (AAS), 3‐methacryloxypropyl trimethoxysilane (ACS), and Bis‐(3‐triethoxylpropyl) tetrasulfan (Si69) were introduced into the wood/NR composites to enhance an interaction between wood sawdust (SD) particles and NR molecules, and to improve the adhesion strength between the SD/NR and EPDM layers. The quantitative evidences were given to explain the changes in the adhesion or peel strengths of the SD/NR‐EPDM laminates through scanning electron microscopy with energy dispersive X‐ray analysis (SEM‐EDS). The experimental results indicated that the suitable cure time and cure temperature for SD/NR‐EPDM melt‐laminates were the tc₉₀ of SD/NR composites and 140°C, respectively. The Si69 coupling agent was found to be the most effective coupling agent as compared with AAS and ACS coupling agents. The Si69 of 0.5 wt% was recommended for the optimizations of the tensile modulus of the SD/NR composites and the peel strength of the SD/NR‐EPDM laminates. The diffusion level between the SD/NR and EPDM layers could be quantitatively substantiated by determining the sulfur content transfer from the SD/NR layer to the EPDM layer. The diffusion and entanglement of molecular chains from the SD/NR to the EPDM layer initiated the co‐crosslinking reaction which played an important role on the changes in the interfacial strength in the SD/NR‐EPDM melt‐laminates. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

门尼粘度及支化程度对三元乙丙橡胶性能的影响

通过无转子硫化仪、橡胶加工分析仪、核磁交联密度仪等分析手段研究三元乙丙橡胶(EPDM)的门尼粘度、长链支化程度对过氧化物硫化EPDM的硫化特性及其硫化胶性能的影响。结果表明,门尼粘度的增加,有助于交联密度和硫化速率的提高,横向弛豫时间不断减小。高支化程度对EPDM胶料硫化速度不利。EPDM门尼粘度越高,初始储能模量G′0越大,储能模量迅速下降的临界应变值越小;不同长链支化度的EPDM硫化胶的储能模量大致相等,但长支化链的损耗因子值相对较高。门尼粘度对EPDM硫化胶拉伸强度变化影响较小;而长链支化程度的提高,使硫化胶拉伸强度和断裂伸长率略微降低。     

动态硫化EPDM/高聚合度PVC热塑性弹性体力学性能的研究

采用动态硫化的方法制备了三元乙丙橡胶（EPDM）/高聚合度聚氯乙烯（HPVC）热塑性弹性体。考察了PVC聚合度、橡塑比、增塑剂添加量、硫化剂用量（质量分数）及不同促进剂配比对体系性能影响,研究了动态硫化工艺条件（硫化时间和硫化温度）对体系性能的影响。实验结果表明：采用动态硫化方法,选用HPVC-2500、橡塑比为30/70、DOP用量为35份、硫化用量为0.4份及合适促进体系,可以制得性能优良的EPDM/HPVC热塑性弹性体,拉伸强度能达到15.18 MPa,断裂伸长率能达到544%。     

Investigation on morphology and mechanical properties of polyamide 6/maleated ethylene‐propylene‐diene rubber/organoclay composites

Maleated ethylene‐propylene‐diene rubber (EPDM‐g‐MA) toughened polyamide 6 (PA6)/organoclay (OMMT) nanocomposites were prepared by melt blending. The role of OMMT in the morphology of the ternary composites and the relationship between the morphology and mechanical properties were investigated by varying the blending sequence. The PA6/EPDM‐g‐MA/OMMT (80/20/4) composites prepared by four different blending sequences presented distinct morphology and mechanical properties. The addition of OMMT could obviously decrease viscosity of the matrix and weaken the interfacial interactions between PA6 and EPDM‐g‐MA when blending EPDM‐g‐MA with a premixed PA6/OMMT nacocomposite, resulting in the increase of rubber particle size. The final mechanical properties are not only determined by the location of OMMT, but also by the interfacial adhesion between PA6 and EPDM‐g‐MA. Having maximum percentage of OMMT platelets in the PA6 matrix and keeping good interfacial adhesion between PA6 and EPDM‐g‐MA are beneficial to impact strength. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Effect of co-agents on adhesion between peroxide cured ethylene–propylene–diene monomer and thermoplastics in two-component injection molding

Two-component (2K) injection-molded products combining ethylene–propylene–diene monomer (EPDM) with polar or nonpolar thermoplastics require strong interfacial bonding. To optimize the adhesion, co-agents trimethylolpropane trimethacrylate (TMPT) and triallyl cyanurate (TAC) are compared and concentrations were varied between 0 and 12 parts per hundred rubber (phr). Changes in material compatibility were characterized by contact angle measurements at high temperature, the adhesion was evaluated by tensile testing, and physicomechanical properties of the EPDM bulk were analyzed. Results show that with polypropylene, the adhesion increases to an optimum (3 phr TAC or 6 phr TMPT) independent of the co-agent type, while for polyethylene only TAC (1.5 phr) effectively boosts adhesion. It is surmised that these optimal concentrations promote crosslinking reactions at the interface. For polycarbonate and acrylonitrile–butadiene–styrene, increasing TAC concentration causes higher adhesion due to improved compatibility. Furthermore, physicomechanical bulk properties change significantly with co-agent concentrations, making the optimal curing composition application dependent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48414.     

Thermal Stability and Crystallization Behavior of TER Blends of Isotactic Polypropylene (iPP)/Ethylene-Propylene Diene Rubber (EPDM)/Nitrile Rubber (NBR)

The blends of isotatic polypropylene (iPP), ethylene-propylene diene rubber (EPDM), and nitrite rubber (NBR) were prepared using dimethylol phenolic resin as a crosslinking system. The dynamically crosslinked blends of iPP/EPDM/NBR showed superior thermal stability to that of virgin isotactic polypropylene (iPP). Dynamic crosslinking rendered the vulcanizate thermally more stable as compared to uncrosslinked blends, which can be attributed due to the variations in degree of crosslinking and degree of crystallinity.

Crystallization of iPP in the blends of iPP/EPDM/NBR was also studied through Temperature Modulated Differential Scanning Calorimetry (TMDSC). Other detailed analysis of endotherm peaks obtained after first and second melts in terms of heat of enthalpy, degree of undercooling, and degree of crystallinity were also evaluated. Various kinetic parameters were also determined. Degree of crosslinking increases the interfacial adhesion between the iPP and EPDM/NBR phases. Dimethylol phenolic resin used as a compatibilizer also enhanced the thermal stability of the iPP/EPDM/NBR blends.     

Rheological behavior and morphological and interfacial properties of PLA/TPE blends

Rheological and interfacial tension data were employed to predict the morphology and thermal and mechanical properties of noncompatibilized and compatibilized poly(lactic acid) (PLA)/thermoplastic elastomer (TPE) blends. PLA was melt blended with thermoplastic polyurethane (TPU) and ethylene elastomer (EE) and compatibilized by ethylene–butyl acrylate–glycidyl methacrylate (EBG) in an internal mixer chamber. Both TPU and EE TPEs have higher viscosities than PLA, and the interfacial properties evaluated have revealed better adhesion between domains of PLA–TPU. The efficiency of the compatibilizer agent EBG depended on the TPE type inferred by modifications in the scanning electron microscopy images of PLA/TPE blends and by the Izod impact strength (improved by 23%). The EBG was more effective in the PLA/TPU blend. The TPEs and EBG did not affect the PLA thermal stability, and no thermal event was observed in the usual PLA extrusion and injection temperature range. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47962.     

EP(D)M structural and thermal property effects in polypropylene compounds

EPDM rubber is an important ingredient in thermoplastic polyolefin elastomers (TPOs). Such key properties as impact strength, flexibility, and flow are significantly affected by EPDM polymer properties. In this work, a set of EPM and EPDM polymer is used to produce via melt processing a series of TPOs, consisting of simple binary blends of rubber and polypropylene of varying composition. Various structural and thermal properties of the EPDM are correlated with the TPO compound properties. Significant property relationships are explored.     

Dynamic mechanical behavior and structure of ternary blends of polypropylene/EPDM rubber/polyethylene

The dynamic mechanical behavior of ternary blends of isotactic polypropylene (80–0 percent)/EPDM rubber (20 percent)/high-density polyethylene (0–80 percent) was investigated in the temperature range from −196 to 100°C by means of a free-oscillating torsional pendulum. The structure of the blends was examined by a scanning electron microscope on etched surfaces cut by a fractured glass edge in liquid nitrogen. Dynamic mechanical response spectra and microphotographs of the systems studied show that the minor thermoplastic forms the core of EPDM rubber inclusions. At 20 percent rubber in the blends, the inclusions can accommodate from 20 to 30 percent polyethylene or polypropylene. Addition of either thermoplastic not exceeding this limit has almost the same effect on the stiffness, damping, and yield stress of the blends as the addition of the same amount of rubber. Ternary blends with equal or slightly different polypropylene and polyethylene fractions have the structure of interpenetrating phases in which EPDM rubber forms the interface layer.     

Studies on Adhesion Between Natural Rubber and Polyethylene and the Role of Adhesion Promoters

Studies on adhesion between natural rubber (NR) and polyethylene (PE) with different levels of interaction (physical and chemical) have been carried out. Ethylene propylene diene rubber (EPDM) and chlorinated polyethylene (CPE) were used as physical promoters and epoxidised natural rubber/modified polyethylene (ENR/PEm) and sulfonated ethylene propylene diene rubber/modified polyethylene (S-EPDM/PEm) were used as chemical adhesion promoters. The failure surfaces were examined with the help of scanning electron microscopy (SEM), optical photography and electron spectroscopy for chemical analysis (ESCA) techniques.

The peel strength between natural rubber and polyethylene as measured in this study is 140 J/m². With the incorporation of physical promoters such as EPDM, the peel strength increases twenty fold because of structural similarity of EPDM with PE and the rubbery nature of EPDM. Similarly, the other promoters show significant improvement in peel strength. At high temperature and low rate of peeling, the nature of failure is mainly “stick-slip” for joints with interaction promoters. The average peel strength increases with increase in test rate and decrease in test temperature for most of the joints. All the data could be shifted onto a master curve indicating that the increase in strength is a result of viscoelastic dissipation. NR/EPDM/PE and NR/CPE/PE systems, however, behave in a different way probably because they alter the nature of crack propagation at or near the interface. ESCA results of the peeled PE surface show a chemical shift of C_1S peak. SEM photographs also indicate interaction at the interface when modifiers are used. An increase in crystallinity of PE from 30% to 64% and modulus increase the peel strength of NR/PE joints by a factor of four. The results of peel strength measurement at 90° are lower than those at 180°. Lap shear results are in line with peel strength.     

Modification of Ethylene Propylene Diene Terpolymer Rubber by Some Thermoplastic Polymers

Abstract

Blends of ethylene propylene diene terpolymer (EPDM) rubber with thermoplastic polyolefins such as low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), high molecular weight polypropylene (PP), and polypropylene random copolymer grade (PP‐R) were prepared by melt mixing. The physico‐mechanical properties, equilibrium swelling in benzene, and aging properties of the binary blends were investigated, analyzing the effect of the rubber/thermoplastics ratio and the type of the thermoplastic material on these properties. The data obtained indicate that EPDM/PP‐R blend in 20/80 w/w% shows the highest physico‐mechanical properties with improved retained tensile strength at 90°C for 7 days. This blend ratio also gives excellent retained equilibrium swelling in benzene at room temperature for 7 days, although EPDM/LDPE blend in 80/20 w/w% imparts the highest retained elongation at break at 90°C for 7 days.