Phase morphology and melt rheological behavior of uncrosslinked and dynamically crosslinked polyolefin blends: role of macromolecular structure

Thermoplastic vulcanizates (TPVs) based on polypropylene (PP) with ethylene–octene copolymer (EOC) and ethylene propylene diene rubber (EPDM) have been prepared by co-agent-assisted peroxide crosslinking system. The study was pursued to explore the influence of two dissimilar polyolefin polymers having different molecular architecture on the state and mode of dispersion of the blend components and their influence on melt rheological properties. The effects of dynamic crosslinking of the PP/EOC and PP/EPDM have been compared with special reference to the concentration of crosslinking agent and ratio of blend components. Morphological analyses show that, irrespective of blend ratio, dynamic vulcanization exhibits a dispersed phase morphology with crosslinked EOC or EPDM particles in the continuous PP matrix. It was found that viscosity ratio plays a crucial role in determining the state and mode of dispersion of blend components in the uncrosslinked system. The lower viscosity and torque values of uncrosslinked and dynamically crosslinked blends of PP/EOC in the melt state indicates that they exhibit better processing characteristics when compared to corresponding PP/EPDM blends.     

Comprehensively improved mechanical properties of silane crosslinked polypropylene/ethylene propylene diene monomer elastomer blends

The properties and structure of silane crosslinked polypropylene (PP)/ethylene propylene diene monomer (EPDM) elastomer blends had been carried out. Fourier transform infrared spectroscopy and gel content tests were employed to evaluate the crosslinking reaction of PP/EPDM blends. Crosslinking efficiency of PP/EPDM blends was investigated using thermogravimetric analysis, differential scanning calorimeter, dynamic mechanical analysis, dynamic rheology, and tensile testing. Tanδ curves of silane crosslinked PP/EPDM blends exhibited an obvious “gel point” originated from the formation of dynamic crosslinking network. The blend corresponding to the “gel point” presented comprehensively improved mechanical properties. These results demonstrated that characteristic rheological parameters showed close correlations with key mechanical properties of silane crosslinked PP/EPDM blends. Scanning electron microscopy images illustrated that crosslinking had remarkably changed the morphologies of PP/EPDM blends. The large deformation mechanism of these blends had been suggested.     

Rheological characterization of the gel point in polymer‐modified asphalts

In this work, the rheological characterization of the gel point in polymer‐modified asphalts is carried out. The viscoelastic properties of polymer‐modified asphalts, in which the polymer is styrene–ethylene butylene–styrene (SEBS) with grafted maleic anhydride (MAH), were measured as a function of MAH concentration. The crosslinking reaction that leads to gelation is characterized by power‐law frequency‐dependent loss and storage modulus (G″ and G′). The relaxation exponent n (a viscoelastic parameter related to the cluster size of the gel) and gel strength S (related to the mobility on the crosslinked chain segments) were determined. The value of the power‐law exponents depends on the composition of polymer, ranging from 0.30 to 0.56, while the value of the rigidity modulus at the gelation point (S) increases with the amount of reactive groups of the modifier polymer. Both n and S are temperature‐dependent in the blends. The blends containing gels present a coarse morphology, which is related to the rheological properties of the matrix and dispersed phase. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology Development via Static Crosslinking of (Polylactic Acid/Acrylic Rubber) as an Immiscible Polymer Blend

The interrelation between crosslinking and morphology is investigated for an immiscible blend of polylactic acid (PLA) and acrylic rubber (ACM). The blends are prepared by solution mixing and static crosslinking is used to avoid the simultaneous effect of the flow field that occurs in dynamic vulcanization. It is carried out at different temperatures, times, and curing agent contents. Scanning force microscopy (SFM) and polarized optical microscopy are used to determine the morphology of the blends. The chemical interactions and viscoelastic properties of the blends after crosslinking are also studied using infrared spectroscopy and rheological tests, respectively. Before crosslinking, SFM shows matrix‐droplet morphology for the samples that it is retained after that for the blend with 30 wt% ACM; however, it is changed to cocontinuous one in the blend with 50 wt% ACM. Partially, grafting of PLA on the crosslinked ACM is confirmed by Fourier transform infrared spectroscopy. The rheological results show that the incorporation of ACM to the PLA slows down the chain relaxation and vulcanization intensifies this effect. A model is proposed to explain the morphology evolution during static crosslinking of an immiscible blend.     

LDPE/PP blends modified by peroxide and radiation induced reactions

LDPE/PP polyblends, modified through either peroxide initiated reactions or irradiation, were characterized in terms of rheological and mechanical properties and microstructure. In the presence of peroxide, or through irradiation LDPE crosslinks, PP degrades. Data were obtained at two peroxide concentration levels (0.1 and 1% by weight) and two radiation doses (30 and 100 kGy). The results show that in peroxide modification, the degradation of PP prevails over the crosslinking of LDPE. However, the effect of irradiation of LDPE (crosslinking) is predominant over that of PP (degradation). The irradiation process tends to yield improved mechanical properties vs. peroxide modification for the PP-rich blends. In addition, the melt viscosity and elasticity of the irradiated PP-rich blends are higher than those of the peroxide-reacted blends at a given level of PP content and frequencies between 10 and 100 rad/s. Attempts were made to relate the shape of the rheological curves and the mechanical properties of the blends to the observed changes in their microstructure. © 1994 John Wiley & Sons, Inc.     

Reactive melt modification of polypropylene with a crosslinkable polyester

Melt blending of polypropylene (PP) with a low molecular weight (MW) crosslinkable unsaturated polyester (UP) was studied in a batch mixer and a twin‐screw extruder in the presence of peroxide (POX) free radical initiator. Competing degradation and crosslinking reactions of the peroxide with the blend components leading to significant change in their viscosity ratio were studied and controlled during the blending process. Rheological studies show that depending on the process conditions some reacted PP/UP blends have a pronounced suspension behavior due to the presence of the dispersed polyester gel particles in a low MW PP matrix. It is also evident from SEM analysis that the reacted blends have a more uniform and finer morphology than the unreacted ones. The blends are also characterized by FTIR, which strongly suggests the presence of “block” or “graft” PP‐UP structures that may enhance phase interaction and promote compatibility in the reacted PP/UP blends. Such blends are considered as suitable compatibilizers of PP/high MW thermoplastic polyester blends and as modifiers for low density extrusion foaming of similar blends.     

Melt viscoelastic properties of peroxide cured polypropylene‐ethylene octene copolymer thermoplastic vulcanizates

The dynamic viscoelastic properties of uncrosslinked and dynamically crosslinked blends of polypropylene (PP) and ethylene octene copolymer (EOC) were investigated in the melt state to study the mechanism of reinforcement, influence of particle size, and kinetics of modulus recovery. Dynamic vulcanization was performed by coagent assisted peroxide crosslinking system. Addition of peroxide in PP/EOC blend involves two major competing reactions: crosslinking in EOC and degradation of PP by β chain‐scission. In this article, morphological and melt rheological properties of the TPVs were studied with special reference to the effect of mixing protocol. Three different mixing techniques were investigated. They are: (i) conventional or preblending method—melt mixing of PP and EOC followed by dynamic vulcanization (ii) phase mixing method—curative master batch of EOC added on the molten PP (iii) split addition of PP—preblending method followed by addition of half part of PP (dilution procedure). The type of mixing protocol has a significant influence on the rheological behavior. Rheological properties have been evaluated at the processing temperature (180°C) in a Rubber Process Analyzer (RPA 2000). A variety of rheological observations such as Payne effect, modulus recovery and shear rate sensitivity were studied by carrying out frequency and strain amplitude sweeps. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Crosslinking of polypropylene–polyethylene blends by peroxide and the effect of pentaerythritol tetrallyl ether

Crosslinking of polypropylene–polyethylene (PP-PE) blends involving 10, 20, 30, 40, 50, 60, 70, 80, and 90% of PP with dicumylperoxide (DCP) or tert-butyl perbenzoate (TBPB) and in the presence of coagent pentaerythritol tetrallyl ether (PETA) was investigated at 180°C. It was found that at lower concentrations of peroxide alone (e.g., 2.5% of DCP) only PE component is crosslinked in all compositions of PP-PE blends. In the crosslinking of PP-PE 50:50 with 4% of TBPB, insoluble gel was obtained, which contained 13% PP and 87% PE. If 2% PETA was also used, the portion of PP in gel increased to 39%; the total yield of gel in PP-PE blend increased from 50 to 70%. The lower crosslinking efficiency of coagent PETA in the PP-PE blends compared with PP alone is associated with better solubility of the coagent in the PE phase in contrast to the PP phase. The coagent does not particularly raise the crosslinking efficiency of peroxide in PE, but increases it in the PP phase. A remarkable decrease in melting temperature and temperature of crystallization of both polymer components depending on peroxide concentration was found by calorimetric measurements.     

The effect of peroxide crosslinking on thermal,mechanical, and rheological properties of polycaprolactone/epoxidized natural rubber blends

Polycaprolactone (PCL)/epoxidized natural rubber (ENR) blends (PCL/ENR = 70/30, 50/50 wt/wt) were prepared by a melt mixing in an internal mixer in the presence of a small amount (0.5 and 1 phr) of dicumyl peroxide. The effect of peroxide crosslinking on thermal, mechanical, and rheological properties of the blends was investigated by means of DSC, tensile test, and small amplitude oscillating rheometer, respectively. It was revealed that peroxide crosslinking enhanced degree of crystallinity of PCL phase and its non-isothermal melt crystallization temperature. The crosslinked blends behave like a thermoplastic elastomer exhibiting high elongation-at-break and fairly good elastic recovery as well as melt processibility. From melt rheological analysis, the peroxide crosslinked blends showed more pronounced shear thinning effect and higher elasticity compared to simple blends.     

Tensile properties and morphology of the dynamically cured EPDM and PP/HDPE ternary blends

The tensile properties and morphology of the polyolefin ternary blends of ethylenepropylene–diene terpolymer (EPDM), polypropylene and high density polyethylene were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured in the presence of PP and HDPE under shear with dicumyl peroxide (DCP). For comparison, blends were also prepared from EPDM which was dynamically cured alone and blended with PP and HDPE later (cure–blend). The effect of DCP concentration, intensity of the shear mixing, and rubber/plastics composition was studied. The tensile strength and modulus increased with increasing DCP concentration in the blends of EPDM-rich compositions but decreased with increasing DCP concentration in blends of PP-rich compositions. In the morphological analysis by scanning electron microscopy (SEM), the small amount of EPDM acted as a compatibilizer to HDPE and PP. It was also revealed that the dynamic curing process could reduce the domain size of the crosslinked EPDM phase. When the EPDM forms the matrix, the phase separation effect becomes dominant between the EPDM matrix and PP or HDPE domain due to the crosslinking in the matrix.     

Reactive extrusion of PP/natural rubber blends

Reactive extrusion of polypropylene (PP)/natural rubber (NR) (90/10) blends was conducted in the presence of a peroxide [1,3-bis(t-butylperoxy)benzene] and coagent (trimethylolpropanetriacrylate, TMPTA). Effects of peroxide and coagent content were studied in terms of melt index (MI), melt viscosity, morphology, thermal, and mechanical properties. At a constant content of the coagent, melt viscosity increased at a low and decreased at a high content of the peroxide. On the other hand, melt viscosity increased monotonically with the coagent concentration at constant peroxide content. The increase and decrease of viscosity were interpreted in terms of crosslinking and chain scission of PP, which governed the rubber domain size and mechanical properties of the reactive blends. © 1995 John Wiley & Sons, Inc.     

LLDPE/POE共混物的交联行为研究

采用过氧化物交联研究了线性低密度聚乙烯(LLDPE)/乙烯-α-辛烯共聚物(POE)共混物。研究了工艺、配方对LLDPE/POE共混物凝胶含量的影响,以及凝胶含量与材料力学性能的关系。结果表明,LLDPE/POE共混物的凝胶含量随引发剂的用量、交联温度和交联时间的增加而增加,达到一定程度后不再增加。在170℃,30min的条件下DCP能充分分解引发交联反应,DCP用量为1.5%时,共混物的凝胶含量可以达到80%以上,再增加时凝胶含量不再增加。DCP的加入顺序对共混物的凝胶含量影响不大。共混物的凝胶含量对其动态力学行为有影响。共混物的凝胶含量对拉伸性能影响不大。     

A reactive extrusion process with the aid of ultrasound for preparing cross‐linked polypropylene

Introducing the crosslinked structure in polypropylene (PP) was highly desired to meet the requirement of high melt strength, which was a key for the application of PP in thermoforming, blow molding and foaming where elongation flows dominated. In this work, the power ultrasound was introduced into the reactive extrusion at the exit die of an extruder for preparing crosslinked PP. The main target was to maintain the highly crosslinked structure during reactive extrusion process in case of low peroxide concentration. The results of the dynamic rheological properties, melt flow index, and extensional viscosity measurement showed that the content of PP gel and the melt strength of PP increased obviously with the employment of a 300 W ultrasound while the contents of functional monomers and peroxide were constant. Fourier transform‐infrared spectroscopy analysis, differential scanning calorimeter characterization, and gel permeation chromatograph measurement proved that the increases of content of PP gel and melt strength of PP were caused by that the ultrasonic waves could induce the chain scission and recombination reaction when the PP melts flowed through the exit die assembled with a ultrasonic probe. POLYM. ENG. SCI., 57:821–829, 2017. © 2016 Society of Plastics Engineers     

动态交联PP/EVA共混物的制备与性能研究

本文将动态交联技术应用于PP/EVA共混体系中,制得动态交联PP/EVA共混物。采用Hakke转矩流变仪研究了动态交联对PP/EVA共混物扭矩的影响;研究了DCP和EVA含量对共混物力学性能的影响;考察了动态交联共混物的维卡软化点。结果表明：加入DCP后,PP/EVA共混物扭矩先升后降,DCP的添加量为EVA含量的1%为宜。随EVA用量的增加,动态交联EVA/PP共混物的冲击强度大幅提高,但拉伸强度有所降低。少量经动态交联的EVA颗粒可以促进共混物中PP的结晶, 提高共混物的维卡软化点。     

Toward Largely Enhanced Toughness and Balanced Strength in PA1012/EPDM Blends via Synergistic Effect of Sacrificial Bonds and Network Structure

Here, zinc-neutralized ethylene propylene diene monomer (EPDM) ionomers with different neutralization levels are prepared through melt blending, and are then incorporated with polyamide 1012 (PA1012) to fabricate PA1012/EPDM ionomer blends. Interestingly, complex crosslinking networks are formed in the blends due to the construction of sacrificial bonds (Zn²⁺-carboxyl, Zn²⁺-amide). The as-formed network structure and sacrificial bond endow the PA/EPDM blends with largely enhanced toughness (16 times higher than that of neat PA), as well as balanced strength and stiffness. Meanwhile, the rheological behaviors of PA1012/EPDM ionomer blends indicate their relative low melting viscosity, which can avoid the processing shortcomings of plastics toughened with rubber. Moreover, PA1012/EPDM ionomer blends show obvious gelation behavior, and a maximum notched Izod impact strength exhibited at the gel point, in which unique double network structure can be observed obviously, indicating that there is a corresponding correlation between the rheological and mechanical parameters. Furthermore, the supper-toughening mechanism of PA1012/EPDM ionomer blends at gel point is explored, which origins from the large deformation and cavitation of rubber particles and the destruction of special double network morphologies. This study provides a novel and effective strategy to fabricate PA materials with outstanding toughness and excellent strength simultaneously.     

The influence of matrix viscosity on properties of polypropylene/polyaniline composite fibers—Rheological,electrical, and mechanical characteristics

Electrically conductive composites containing polypropylene (PP) and polyaniline (PANI) were prepared using PP with three different melt flow rates (MFRs) and a commercial PANI‐complex in proportions of 80% by weight and 20%, respectively. Composite blends were melt‐spun to fibers under different solid‐state draw ratios. Rheological studies of dynamic viscosity, as well as the storage modulus and loss modulus showed that the prepared PANI‐complex/PP blends exhibit different dynamic rheological behavior, depending on the PP used. This confirms the blends' morphological differences. PP matrix viscosity was found to play an important role in the electrical properties of the prepared fibers. Fibers prepared using the matrix with the lowest viscosity, showed a larger dispersed phase size in the cross‐sectional SEM micrographs, maximum conductivity observed at higher draw ratios and a more linear resistance–voltage relationship than those of the fibers prepared using the higher viscosity matrices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of dynamic vulcanization on the microstructure and performance of polyethylene terephthalate/elastomer blends

Blends of polyethylene terephthalate (PET) and ethylene‐ethyl acrylate‐maleic anhydride terpolymer (E‐EA‐MAH) were dynamically crosslinked in a one‐step extrusion process. An amine‐terminated glycol reacting with MAH moieties was used as the crosslinking agent. The effect of blend composition and dynamic crosslinking on the microstructure and mechanical properties were investigated. Blend ratios ranging from 80:20 to 20:80 PET/E‐EA‐MAH were studied. The region of phase inversion was located for uncrosslinked and dynamically crosslinked blends. The rheological characterization was also carried out for these blends in comparison with the neat materials. After dynamic crosslinking, the phase inversion is shifted from the 30–40% range to the 70–80% range of elastomer content. This shift is induced by the increase of viscosity and elasticity of the network formed. Dynamically crosslinked blends show significant improvements in impact strength but also exhibit a decrease in elongation at break.     

The Effect of Dicumyl Peroxide Vulcanization on the Properties & Morphology of Polypropylene/Ethylene-Propylene Diene Terpolymer/Natural Rubber Blends

ABSTRACT

This article discusses some properties such as tensile properties, chemical and oil resistance, gel content, crystallinity, and morphology of polypropylene (PP)/ethylene-propylene diene terpolymer (EPDM)/natural rubber (NR) blends. Dicumyl peroxide (DCP) was applied as a crosslinking agent. In terms of tensile properties, peroxide vulcanized blend shows higher tensile strength and tensile modulus (stress at 100% elongation, M₁₀₀) as compared with the unvulcanized blend. The elongation at break of the peroxide vulcanized blend is higher for the blend with NR rich content compared with the EPDM rich content. The improvements in chemical and oil resistance as well as gel content of peroxide vulcanized blends have also proved the formation of crosslinks in the rubber phase. Scanning electron microscopy (SEM) micrographs from the surface extraction of the blends support that the crosslinks have occurred during dynamic vulcanization. Dynamical vulcanization with DCP has decreased the percent crystallinity of blends that can be attributed to the formation of crosslinks in the rubber.     

Microscopic morphology,rheological behavior,and mechanical properties of polymers: Recycled acrylonitrile-butadiene-styrene/polybutylene terephthalate blends

In this study, styrene-acrylonitrile-glycidyl methacrylate (SAG) series copolymers were specially designed for producing the recycled acrylonitrile-butadiene-styrene (rABS)/poly(butylene terephthalate) (PBT)/SAG blends, which were prepared through the process of continuous melt blending and batch feeding. The effects of viscosity composition, SAG chemical composition, and SAG content on the morphology, and rheological and mechanical properties of the blends have been investigated. As demonstrated by morphological observation, the variety of viscosity composition of the blends affects the size of dispersed PBT droplets. Moreover, high viscosity of rABS matrix seems to facilitate the formation of smaller dispersed phase size of blends. Various SAG chemical compositions have different stabilities on the morphology of the blends, which affects the deformation, fragmentation, and coalescence of dispersed phase droplets. In addition, a finer phase morphology can be achieved when the density distribution of epoxy group is optimal in SAG copolymer. Rheological characterization manifested that the rheological properties of the blends depends strongly on its composition and structure, while the crosslinking degree is associated with the concentration of reactive groups and extent of reaction. Thereby, the rheological behavior of the blends during processing can be controlled by changing the reactive sequence and adding the quantity of epoxy group. The test on mechanical properties verified that a recycled product with excellent performance can be obtained by altering processing methods and the blends formula, which may be further applied to the 3D printing materials required by fused deposition modeling technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48310.     

Effects of linear low density polyethylene on physical properties and irradiation effectiveness of polypropylene

Blends of polypropylene (PP)/linear low density polyethylene (LLDPE) were prepared by melt mixing in twin screw extruder at 190 °C. Polyfunctional monomer TMPTMA (trimethylolpropane-trimetacrylate) was added to the mixture as a crosslinking co-agent to improve the crosslinking or branching efficiency of the olefins during irradiation. The effect of LLDPE on the crosslinking or branching effectiveness and physical properties of PP was investigated in conjunction with the monomer content of LLDPE in the blends. Thermal stability, rheological properties and electron beam irradiation effectiveness of PP in presence of LLDPE were analyzed by DSC, TGA and RDS. Solution gel analysis and the presence of ?C=O in FT-IR test supported some crosslinking or branching that occurred after irradiation. Certain decrease in melting temperature (T _m ) that was noticed after irradiation could have been the result of chain scissioning, which decreases the number of tie molecules in the amorphous region and consequently weakens the lamellar connections. Shear thinning effect and zero shear viscosity were improved by irradiation in the PE incorporated samples.