Thermal stability and miscibility in PVC/EVA blends

Thermal stability and degradation processes in PVC/EVA systems were evaluated for a series of EVAs with different vinyl acetate contents. The experimental data revealed a relationship between the thermogravimetric curves and the degree of interaction in the mixtures as compared to the pure polymers, which is consistent with the results of microscopic analysis. Kinetic parameters and lifetime data on the mixtures were also calculated.     

Study of the α-relaxation of PVC, EVA and 50/50 EVA70/PVC blend

The dipole dynamics and α-relaxation behaviour of polyvinyl chloride PVC, poly(ethylene-co-vinyl-acetate) EVA₇₀ and blend of them EVA₇₀/PVC have been investigated by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). The differential scanning calorimetry (DSC) thermograms measured on samples show a single glass transition in the analysed temperature range. These three polymers are wholly amorphous and pure PVC and pure EVA₇₀ are miscible in the ratio 1:1. The glass transition temperature T_g decreases significantly with presence of EVA₇₀. Furthermore, the values of apparent activation energies for molecular motions at the α-relaxation and the values of fragility index have also been determined for each sample using Moynihan expression for DSC results and Vogel-Fulcher-Tammann-Hesse (VFTH) form for DRS results. It is shown a large dependence of all the values of these parameters with the content of EVA₇₀. Comparing these three polymers, we found that the more fragile glass forming liquid is the PVC. Fragility decreases drastically with EVA₇₀ content. EVA₇₀ and EVA₇₀/PVC blend exhibit practically the same behaviour. The effect of inter- and intra-molecular interactions on fragility is discussed to explain these variations.     

Rheology, morphology and mechanical properties of polyethylene/ethylene vinyl acetate copolymer (PE/EVA) blends

Rheology, morphology and mechanical properties of binary PE and EVA blends together with their thermal behavior were studied. The results of rheological studies showed that, for given PE and EVA, the interfacial interaction in PE-rich blends is higher than EVA-rich blends, which in turn led to finer and well-distributed morphology in PE-rich blends. Using two different models, the phase inversion composition was predicted to be in 45 and 47 wt% of the PE phase. This was justified by morphological studies, where a clear co-continuous morphology for 50/50 blend was observed. The tensile strength for PE-rich blends showed positive deviation from mixing rule, whereas the 50/50 blend and EVA-rich blends displayed negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The elongation at break was found to follow the same trend as tensile strength except for 90/10 PE/EVA blend. The latter was explained in terms of the effect of higher co-crystallization in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. The results of thermal behavior of the blends indicated that the melting temperatures of PE and EVA decrease and increase, respectively, due to the dilution effect of EVA on PE and nucleation effect of PE on EVA.     

Comparative study of pyrolytic decomposition of polymers alone or in EVA/PS,EVA/PVC and EVA/cellulose mixtures

The behavior of mixtures of EVA–PS, EVA–PVC and EVA–cellulose in various proportions were investigated under pyrolysis. A kinetic model with an independent pathway is proposed for the weight loss and compared with the experimental and theoretical results obtained in a previous study with individual polymers. The kinetic parameters were determined and online IR spectrometric analysis used to follow the evolution of the gaseous pyrolysis products versus the temperature. The result shows good agreement for the EVA–PS mixture and confirms the hypothesis of an independent pathway. However, in the case of EVA–PVC and EVA–cellulose mixtures, the polymers affect one other in the pyrolysis reaction.     

Thermal,rheological, morphological and mechanical properties of high density polyethylene/ethylene vinyl acetate copolymer (HDPE/EVA) blends

Thermal, rheological, morphological and mechanical properties of binary HDPE and EVA blends were studied. The results of rheological studies showed that for given HDPE and EVA, the interfacial interaction in HDPE-rich blends is higher than EVA-rich blends. Using three different rheological criterions, the phase inversion composition was predicted to be in 30 wt% of the EVA phase. This showed good agreement with morphological studies. The tensile strength for HDPE-rich blends showed positive deviation from mixing rule, whereas the EVA-rich blends played negative deviation. These results were in a good agreement with the results of viscoelastic behavior of the blends. The thermal analysis revealed that high co-crystallizaiton in 90/10 composition, which increased the tensile strength and decreased the elongation at break in this composition. Furthermore, the results of thermal behavior of the blends indicated that the melting temperatures of HDPE decrease due to the dilution effect of EVA on HDPE.     

Rheology and stability of bitumen/EVA blends

Rheological measurements reveal that the viscoelastic properties of a 60/70 penetration grade bitumen are improved when either a virgin EVA or a recycled EVA copolymer of similar vinyl acetate content are mixed with it. Risk of cracking at low temperatures and rutting at high temperatures, are both reduced. Better viscoelastic features are obtained with the bitumen modified with recycled EVA, probably due to the presence of carbon black, which acts like a filler in this material. Stability tests performed combining oscillatory flow and microscopy results disclose that blends with the higher polymer proportion (3%) are susceptible of phase separation after 24 h of storage at 165 °C, but 1% blends are stable for at least 4 days. A general evaluation of the results indicates that the performance of this bitumen as a binder for road pavement, is particularly improved when 1% of recycled EVA or virgin EVA is added.     

Deviations from bulk morphologies in thin films of block copolymer/additive binary blends

Deviations from bulk morphologies in thin films of binary blends of alkyne-functionalized diblock copolymer poly(ethylene oxide)-block-poly(n-butyl methacrylate-random-propargyl methacrylate) (PEO-b-P(nBMA-r-PgMA)) and Rhodamine B azide are reported, where thermal click reaction between the two components leads to microphase separated morphologies. Both in the bulk and in thin films, increasing the azide loading ratio resulted in the transition from a lamellar microdomain morphology to a hexagonally packed cylindrical mircodomain morphology. However, in thin films the lamellae-cylinder transition was observed at a different azide loading ratio, which was determined by film thickness. As a result, significant deviations from the bulk morphology were observed. These results indicate that surface interactions and confined geometry can play an important role in dictating the morphology in thin films of BCP/additive binary blends.     

Thermogravimetric analysis of PVC/ELNR blends

The thermal behaviour of a series of solution-cast blends of polyvinyl chloride/epoxidised liquid natural rubber (ELNR) of different mole percentage of epoxidation has been examined using thermogravimetric analysis. Thermal degradation is found to occur through a two-step route in which the first step corresponds to the dehydrochlorination of PVC to form a polyene and the second step is attributed to the decomposition of the ELNR and the polyene. Introduction of 20 and 50 mol% of epoxy group into the liquid NR is found to enhance the thermal stability of PVC. Probable mechanisms of degradation have been suggested on the basis of the kinetic analysis of the degradation studies. It is found that the mechanism is influenced by the epoxy content of the blend system. Activation energy for the degradation and the entropy change have also been reported.     

Monte Carlo simulation on symmetric ABA/AB copolymer blends in confined thin films

The effects of blend composition on morphology, order-disorder transition (ODT), and chain conformation of symmetric ABA/AB copolymer blends confined between two neutral hard walls have been investigated by lattice Monte Carlo simulation. Only lamellar structure is observed in all the simulation morphologies under thermodynamic equilibrium state, which is supported by theoretical prediction. When the composition of AB diblock copolymer (phi) increases, both lamellar spacing and the corresponding ODT temperature increase, which can be attributed to the variation of conformation distribution of the diblock and the triblock copolymer chains. In addition, both diblock and triblock copolymer, chains with bridge conformation extend dramatically in the direction parallel to the surface when the system is in ordered state. Finally, the copolymer chain conformation depends strongly on both the blend composition and the incompatibility parameter chiN.     

Miscibility studies of PVC/Aramid blends

Blends containing PVC and aramid (Ar) matrices were probed for their miscibility. In this respect, Ar chains were synthesized by aromatic diamine and diacid chloride in amide solvent. The Ar thus synthesized was characterized through Fourier transform infrared (FTIR) spectroscopy and molecular weight determination. Blend system Ar/PVC was investigated over a range of Ar/PVC ratios. Their mechanical profiles in terms of maximum stress, maximum strain, toughness, and initial moduli have been explored. Thermal properties and morphology of the blends were estimated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). A good correlation was observed between thermal, mechanical, and morphological properties of the blends. The presence of hydrogen bonding among polymers was evaluated through FTIR spectroscopy, which is believed to be responsible for the blend miscibility. Optimal thermal and mechanical profiles were depicted by the blend containing 40-wt% PVC in the Ar matrix.     

Thermogravimetric analysis of PVC/NR-b-PU blends

Thermal stability of solution-cast blends of poly(vinylchloride) and NR-b-PU block copolymers of three different chain extender diols was studied by thermogravimetry. Thermal degradation of individual components and their blends were investigated with special reference to blend ratio. As the block copolymer content in the blends increased their thermal stability was also found to increase. Enhanced thermal stability of PVC is believed due to the favorable interaction with PVC and the PU hard segments of the block copolymer. DTG curves were used for the determination of different stages involved in the degradation. Activation energy for degradation was determined from Coats–Redfern plot.     

PVC/EVA/SBS共混体系研究

利用溶液成膜法制备了PVC/SBS薄膜 ,对其表观形态、力学性能进行了研究 ,并讨论了EVA对体系的增容作用。发现EVA在一定浓度范围内能增加PVC与SBS的相容性 ,提高断裂伸长率 .测量了溶液的相对粘度 ,得出了相反转浓度点。     

Electronic transport properties of polyaniline/PVC blends

The electrical conductivity and thermoelectric power of polyaniline/PVC blends was measured. Surprisingly, the conductivity of the blends is greater at low temperatures than that of the pure polyaniline sample. The conductivity follows approximately an exp (?T^?1/2) law over a considerable range of temperature, with deviations from this law observed at high temperature increases (with positive sign) except at very low temperatures, where negative peaks are observed. Possible models to interpret these observations are mentioned. © 1993 John Wiley & Sons, Inc.     

乙烯醋酸乙烯酯/聚氯乙烯共混体系相容性、相逆转及其物理力学性能研究

<正> 硬质聚氯乙烯(PVC)由于韧性较差通常要用改性剂改善其抗冲击性能。但要使改性剂能有效起到作用,必须考虑它与PVC之间的相容性及其配比等对共混物性能的影响。本工作从动态力学及其他物理力学性能,研究了含48%醋酸乙烯(VAc)的乙烯醋酸乙烯酯共聚物(EVA)与PVC共混时组分之间的相容性及其配比对体系相逆转及其物理力学性能的影响。 样品:PVC采用北京化工二厂生产的SX-4型粉料。EVA粒料中的VAc重量含量为48%。将这两种料按不同的比例,加上助剂(二盐基亚磷酸铅、三盐基硫酸铅、硬     

Controlling final morphologies of two-step polymerization induced phase separated blends of trimethylolpropane triacrylate/acrylate copolymer through copolymer molecular weight

Effect of molecular weight of a thermoplastic copolymer on final morphology of polymerization induced phase separation of trimethylolpropane triacrylate/copolymer blends have been studied. Two acrylate copolymers, ACHM and ACLM, mainly based on methyl methacrylate, butyl acrylate and styrene were synthesized with high and low molecular weight, respectively. Final morphology of TMPTA/ACHM and TMPTA/ACLM blends were investigated by optical microscopic observation of ensemble of surface and bulk phase separation status points of view. Image analysis were done to provide related characteristic length scales.Polymerization induced phase separation of TMPTA/ACHM and TMPTA/ACLM resulted in different final morphologies with different characteristic length scales, which was attributed to the kinetic effect of the copolymer chains mobility during two-step phase separation induced during the thermal history and UV-irradiation periods.     

Study of phenolic resin/EVA blends by thermal analysis

The properties of polymeric blends originate from the synergistic association of their components. In this investigation, phenolic resins obtained by the reaction of cashew-nut shell liquid (CNSL) and aldehyde are used in several applications. Mixtures of CNSL with industrial reject ethylene-co-vinyl acetate (EVA reject) were prepared with an EVA reject content up to 70%. The thermal compatibility and stability were evaluated by means of thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). For blends containing a high percentage of EVA reject, the TG curves clearly show two decomposition stages, one at 350C and the other at 450C (onset 467C). The DIG curves of the blend containing 70% CNSL exhibit decomposition at 240C. The DSC curves show that the samples containing a high percentage of EVA reject are incompatible, withT _g values around –30C.The authors would like to thank PETROBRAS/CENPES/DIQUIM for the NMR facilities and thermal measurements.     

Evaluation of the SEBS copolymer in the compatibility of PP/ABS blends through mechanical,thermal, thermomechanical properties,and morphology

Polypropylene (PP) blends with acrylonitrile-butadiene-styrene (ABS) were prepared using the styrene-ethylene-butylene-styrene copolymer (SEBS) as a compatibilizing agent. The blends were prepared in a co-rotational twin-screw extruder and injection molded. Torque rheometry, Izod impact strength, tensile strength, heat deflection temperature (HDT), differential scanning calorimetry, thermogravimetry, and scanning electron microscopy properties were investigated. The results showed that there was an increase in the torque of PA6/ABS blends with SEBS addition. The PP/ABS/SEBS (60/25/15%) blend showed significant improvement in impact strength, elongation at break, thermal stability, and HDT compared with neat PP. The elastic modulus and tensile strength have not been significantly reduced. The degree of crystallinity and the crystalline melting temperature increased, indicating a nucleating effect of ABS. The PP/ABS blends compatibilized with 12.5% and 15% SEBS presented morphology with well-distributed fine ABS particles with good interfacial adhesion. As a result, thermal stability has been improved over pure PP and the mechanical properties have been increased, especially impact strength. In general, the addition of the SEBS copolymer as the PP/ABS blend compatibilizer has the advantage of refining the blend's morphology, increasing its toughness and thermal stability, without jeopardizing other PP properties.     

PVC/MBS共混物的紫外光交联及光氧化反应

PVC及其共混物应用广泛,MBS作为PVC制品的透明抗冲改性剂,在提高PVC抗冲性能的同时,必然影响PVC在紫外光照下发生的光化学反应过程,我们用紫外可见光研究了MBS对PVC紫外光解脱HCl动力学,发现MBS对PVC光解脱HCl有抑制作用,本文利用FTIR光谱研究PVC／MBS共混体系中,MBS对PVC光氧化、光交联及光降解过程的影响。     

Development and characterization of reactive extruded PVC/polyacrylate blends

This paper describes a method to obtain polymer blends by the absorption of a liquid solution of monomer, initiator, and a crosslinking agent in suspension type porous poly(vinyl chloride) (PVC) particles, forming a dry blend. These PVC/monomer dry blends are reactively polymerized in a twin‐screw extruder to obtain the in situ polymerization in a melt state of various blends: PVC/poly(methyl methacrylate) (PVC/PMMA), PVC/poly(vinyl acetate) (PVC/PVAc), PVC/poly(butyl acrylate) (PVC/PBA) and PVC/poly(ethylhexyl acrylate) (PVC/PEHA). Physical PVC/PMMA blends were produced, and the properties of those blends are compared to reactive blends of similar compositions. Owing to the high polymerization temperature (180°C), the polymers formed in this reactive polymerization process have low molecular weight. These short polymer chains plasticize the PVC phase reducing the melt viscosity, glass transition and the static modulus. Reactive blends of PVC/PMMA and PVC/PVAc are more compatible than the reactive PVC/PBA and PVC/PEHA blends. Reactive PVC/PMMA and PVC/PVAc blends are transparent, form single phase morphology, have single glass transition temperature (T_g), and show mechanical properties that are not inferior than that of neat PVC. Reactive PVC/PBA and PVC/PEHA blends are incompatible and two discrete phases are observed in each blend. However, those blends exhibit single glass transition owing to low content of the dispersed phase particles, which is probably too low to be detected by dynamic mechanical thermal analysis (DMTA) as a separate T_g value. The reactive PVC/PEHA show exceptional high elongation at break (～90%) owing to energy absorption optimized at this dispersed particle size (0.2–0.8 µm). Copyright © 2005 John Wiley & Sons, Ltd.     

Heat shrinkability of electron-beam-modified thermoplastic elastomeric films from blends of ethylene-vinylacetate copolymer and polyethylene

The heat shrinkability of electron-beam-irradiated thermoplastic elastomeric films from blends of ethylene–vinylacetate copolymer (EVA) and low-density polyethylene (LDPE) has been investigated in this paper. The effects of temperature, time and extent of stretching and shrinkage temperature and time have been reported. Based on the above data, the optimized conditions in terms of high heat shrinkage and low amnesia rating have been evaluated. Influence of radiation doses (0–500 kGy), multifunctional sensitizer levels (ditrimethylol propane tetraacrylate, DTMPTA), and blend proportions on heat shrinkability has been explained with the help of gel fraction and X-ray data. With the increase in radiation dose, gel fraction increases, which in turn gives rise to low values of heat shrinkage and amnesia rating. At a constant radiation dose and blend ratio, percent heat shrinkage is found to decrease with increase in DTMPTA level. Gel content increases with the increase in EVA content of the blend at a constant radiation dose and monomer level, giving rise to decrease in heat shrinkability. Heat shrinkage increases with the increase in percent crystallinity, although the amnesia rating follows the reverse trend.