Dynamic mechanical behavior of the dioctyl phthalate plasticized polyvinyl chloride-epoxidized soya bean oil

The mixing of polyvinyl chloride (PVC) with dioctyl phthalate (DOP) shows two stages of gelation and fusion, but the homogeneity of each stage is influenced by the thermal stability of PVC and its rheological behavior. A torque rheometer has been used to gather almost all critical data related to the plasticized PVC in the epoxidized soya bean oil (ESBO). This study shows that, rheological data reflects the effects of DOP and epoxidization levels of SBO, in a DOP plasticized PVC-ESBO. The DOP plasticizer forms a thermodynamically miscible solution with ESBO; that reduces the rate of fusion and torque at balance of PVC. The storage modulus and tanδ of the plasticized PVC-ESBO have been used to show the extent of the homogeneity; but the dynamic mechanical behavior of PVC-ESBO is strongly influenced by DOP and the epoxidization level of SBO. The glass transition temperatures and dynamic properties of DOP plasticized PVC-ESBO are also reported and discussed in terms of the thermal stability and homogeneity of PVC.     

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers

Dynamic percolation in highly oriented conductive networks formed with different carbon nanofillers is investigated during disorientation upon annealing. Conductive networks are constructed by solid-state drawing, subsequent annealing, and using fillers with different dimensions (multiwalled carbon nanotubes (MWCNTs) and carbon black (CB)) in a bicomponent tape. Interestingly, it is observed that a less entangled network work is formed by mixed filler containing CB; consequently, this result in an accelerated dynamic percolation process and reduced activation energy of such process. Three different analytical approaches have been utilized to analyze this interesting behavior. It is concluded that the dynamic percolation process in highly oriented conductive polymer composites filled with MWCNTs can indeed be accelerated by the addition of CB, since less entangled networks are formed in a hybrid filler system compared with MWCNTs alone.     

Liquid crystals: first active organics in electronics

A Commentary on the paper “Anisotropic gels and plasticized networks formed by liquid crystal molecules”, by R. A. M. Hikmet. First published in Liquid Crystals, 9, 405-416 (1991).     

Liquid crystals: first active organics in electronics

A Commentary on the paper “Anisotropic gels and plasticized networks formed by liquid crystal molecules”, by R. A. M. Hikmet. First published in Liquid Crystals, 9, 405–416 (1991).     

Polymerization and viscoelastic behavior of networks from a dual‐curing,liquid crystalline monomer

The network formation and viscoelastic behavior of a liquid crystalline monomer, whose structure includes both acrylate and acetylene reactive groups, have been studied. By combining both photo and thermal polymerization, the networks can be formed in two separate steps, with the initial photopolymerization dominated by acrylate crosslinking and subsequent thermal polymerization dominated by acetylene crosslinking. In addition, the monomer exhibits a liquid crystalline phase. Photopolymerization while in the liquid crystal phase locks in the molecular ordering. Dynamic mechanical analysis shows that networks formed from the liquid crystalline phase have lower crosslink densities and narrower distributions of molecular weights between crosslinks when compared to networks formed from the isotropic phase (and at higher polymerization temperatures). After thermal postcure at 250°C, the networks formed from the isotropic monomer have a 23% higher dynamic mechanical storage modulus (in the glassy state) than the networks formed from the liquid crystalline monomer. The thermally postcured networks have unusually high glass‐transition temperatures, which exceed 300°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1183–1190, 1999     

Plasticized polylactide/clay nanocomposites. I. The role of filler content and its surface organo‐modification on the physico‐chemical properties

Polylactide (PLA)‐layered silicate nanocomposites plasticized with 20 wt % of poly(ethylene glycol) 1000 were prepared by melt blending. Three kinds of organo‐modified montmorillonites—Cloisite® 20A, Cloisite® 25A, and Cloisite® 30B—were used as fillers at a concentration level varying from 1–10 wt %. Neat PLA and plasticized PLA with the same thermomechanical history were considered for comparison. Nanocomposites based on amorphous PLA were obtained via melt‐quenching. The influence of both plasticization and nanoparticle filling on the physicochemical properties of the nanocomposites were investigated. Characterization of the systems was achieved by size exclusion chromatography (SEC), thermogravimetric analysis (TGA), thermally modulated differential scanning calorimetry (TMDSC), X‐ray diffraction (XRD), and dynamic mechanical analysis (DMTA). SEC revealed a decrease of the molecular weight of the PLA matrix with the filler content. Thermal behavior on heating showed one cold crystallization process in the reference neat PLA sample, while two cold crystallization processes in plasticized PLA and plasticized nanocomposites. The thermal windows of these processes tend to increase with the filler content. The crystalline form of PLA developed upon heating was affected neither by the plasticization nor by the type and content of Cloisite used. It was found that the series of organo‐modified montmorillonites with decreasing affinity to PLA is Cloisite® 30B, Cloisite® 20A, and Cloisite® 25A, respectively. The dynamic mechanical properties were sensitive to the sample composition. Generally, the storage modulus increased with the filler content. Glassy PEG, well dispersed within unfilled PLA matrix, exhibited also a reinforcing effect, since the storage modulus of this sample was higher than for unplasticized reference at temperature region below the glass transition of PEG. Moreover, loss modulus of all plasticized samples revealed an additional maximum ascribed to the glass transition of PEG–rich dispersed phase, indicating partial miscibility of organic components of the systems investigated. The magnitude of this mechanical loss was correlated with the filler content, and to some extent, also with the nanofiller ability to be intercalated by polymer components. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 299–311, 2006     

Anisotropic electroconducting polymer-silicate composites based on polyaniline

Approaches for the development of anisotropic electroconducting composite materials based on polyaniline and Na-montmorillonite prepared by the me thods of boundary and intercalation polymerization of aniline and mechanical blending are proposed. Parallel plane compression of solid and plasticized dispersions is shown to lead to the development of primarily planar ordering of anisometric clay particles with sorbed or intercalated polymer; as a result, nanocomposites with anisotropic electrical conductivity are formed. In the prepared polymer-silicate films, the parameter of anisotropy in electrical conductivity achieves 6 × 10³.     

Effect of annealing on microstructure and mechanical properties of polypropylene random copolymer

In this work, polypropylene random copolymer (PPR) was taken as an example to study the changes of mechanical properties related to its microstructure evolution. Firstly, the toughness and fracture morphology were analyzed by notched Izod impact test and scanning electron microscope. Annealing at relative lower temperatures (<100°C), mechanical properties are slightly enhanced, which should be pointed out that significant improvements have been observed when annealing at relative higher temperatures (>100°C). Secondly, the study was conducted from the conventional differential scanning calorimetry, wide angle X-ray diffraction, and small-angle X-ray scattering to analyses the changes in the crystalline and amorphous regions. Dynamic thermomechanical analysis was employed to explore the changes of molecular mobility in samples after annealing at different temperatures. Moreover, to find out the stress transfer between the crystalline regions and the amorphous regions, we did further analysis of the typical stress–strain curves and proposed the mechanism of microstructure evolution during annealing process. The results shown that amorphous rearranged and formed thinner lamellae when annealing at relative low temperature. While annealing at higher temperatures, the mobile and rigid amorphous regions rearranged into more perfect lamellae and the density of stress transmitters was increased significantly.     

Correlation between static mechanical properties of starch-glycerol materials and low-temperature relaxation

Mechanical, calorimetric, dynamic mechanical and dielectric properties were measured in starch and amylose films plasticized by different glycerol contents. Low-temperature relaxation was found to be highly dependent on plasticizer level and related to unusual mechanical properties.     

Topological aspects of structure and properties of highly crosslinked networks

Statistical model approach which allows to set the quantitative interrelation between the chemical structure of initial reagents, formation mechanism, topology and in the final analysis mechanical properties of highly crosslinked networks, is considered. The role of network topology in the formation of the main physico-mechanical properties of polymer network is singled out. The analysis is carried out on the important class of highly crosslinked networks, formed by polyaddition reaction of diepoxides with aromatic diamines.     

Simulation of phase behavior and mechanical properties of ideal interpenetrating networks

In this work microphase separation in ideal interpenetrating networks as well as its influence on the mechanical properties of the networks has been studied. Structures with long-range order in such networks have not been found to be formed; the reason for this is apparently the weak bonding (physical entanglements) between the subnetworks. The dynamics of the relaxation of interpenetrating networks with highly incompatible subnetworks has been studied and it has been found that the slow rearrangement of phase boundaries during the stretching process has a significant influence on it. Using the analysis of subchains conformations, it has been found that the increase in the stiffness of interpenetrating networks with incompatible subchains occurs due to the irregular tension of subchains related to the presence of big aggregates in the system.     

Liquid crystal fibers produced by using electrospinning technique

This paper investigates the electrospinning process of liquid crystalline polysiloxane with cholesterol as side chain (LCPC) and the influence on the morphology of the formed fibers by mixing LCPC solution with small-molecule liquid crystal, triethylamine, and poly(ethylene oxide)(PEO). The mechanical properties of single fibers were characterized by a novel approach. The results indicate that, under appropriate conditions, fine liquid crystal fibers can be obtained and the preferable mechanical properties can be achieved, especially after annealing. WXRD was used to investigate the orientation of polymer molecules in the formed fibers, suggesting that strong interaction exists between LCPC and PEO molecule in the resulting composite fibers, and polymer molecular tends to arrange regularly during electrospinning processing. This research work provides a new and facile method of using electrospinning to prepare liquid crystal fibers, which would be useful for designing the related high-performance materials.     

Influence of thermal history on mesoscale ordering in polydomain smectic networks

Dramatic changes in mesoscale ordering and macroscopic mechanical behavior are observed in smectic polydomain networks after annealing at a temperature well above the glass transition temperature but below the clearing temperature. Tensile testing reveals gradual stiffening and loss of extensibility, and X‐ray linewidth measurements confirm that stiffening is initially due to thickening of domains. At long annealing times, a more highly ordered smectic mesophase forms, further stiffening the networks and reducing their extensibility. Increasing the concentration of (flexible) crosslinkers hinders domain growth and suppresses formation of the higher order mesophase, a useful guideline for design of smectic networks that exhibit reduced sensitivity to thermal history. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Morphology development in thermoplastic vulcanizates (TPV): Dispersion mechanisms of a pre-crosslinked EPDM phase

The fragmentation and dispersion in molten polypropylene (PP) of several pre-crosslinked and plasticized ethylene–propylene–diene terpolymer (EPDM) networks was studied. Thus, the morphologies and mechanical properties of PP/EPDM blends having similar compositions but made from either un-crosslinked, pre-crosslinked or dynamic-crosslinked EPDMs were compared. The results first highlight the importance of the gel fraction of the pre-crosslinked EPDMs, as well as the impact of the thermoplastic matrix proportion on the quality of the dispersion of such networks. As a result, pre-crosslinked EPDM having a gel fraction below g_EPDM = 0.7 can be finely and homogeneously fragmented and dispersed in presence of PP. It can be then admitted a collision–coalescence–separation type erosion mechanism of the EPDM domains. Nevertheless, contrarily to some theoretical model expectations, a partial fragmentation of the chemical networks was always observed even at very high crosslink density (g_EPDM > 0.7). Finally, the blends crosslinked under shearing (dynamic-crosslinked) showed a clear mechanical property synergy due to their fine and homogeneous morphology coupled with the full crosslinking of the elastomer. In the end, these results brought significant information on TPV morphology stabilization and their related mechanical properties.     

Effects of thermal annealing on the viscoelastic properties and morphology of bimodal hard/soft latex blends

The effects of thermal annealing on the viscoelastic properties and morphology of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles with controlled sizes were investigated. The thermal and viscoelastic properties of as‐dried and annealed samples were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). Throughout the thermal annealing, the latex blend morphologies were also followed with atomic force microscopy and transmission electron microscopy (TEM). A particulate morphology, consisting of hard particles evenly dispersed in a continuous soft phase, was observed in the TEM micrographs of the as‐dried latex blends and resulted in an enhancement of the mechanical film properties at temperatures between the α relaxations of the soft and hard phases in the DMA thermograms. As soon as the thermal annealing involved temperatures higher than the glass‐transition temperature of the hard phase, the hard particles progressively lost their initial spherical shape and formed a more or less continuous phase in the latex blends. This induced coalescence of the hard particles was confirmed by the association of the experimental viscoelastic data with theoretical predictions, based on self‐consistent mechanical models, which were performed by the consideration of either a particulate or cocontinuous morphology for the bimodal latex blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2289–2306, 2005     

磺化丁基橡胶离聚体及其共混物的动态力学性质

<正> 含10％摩尔以下的离子且主链为柔性的离聚体是一种热塑性弹性体。在动态力学性质方面呈现特殊的行为,表现在贮能模量(1gE′)与温度的关系中有橡胶态平台出现。最早Otocka等指出,(丁二烯-甲基丙烯酸)共聚物无橡胶态平台,经金属离子中和后产生橡胶态平台,且E′增加。Agarwal,Makowski等则报道磺化乙丙胶离聚体的橡胶态平台随离子含量提高而加宽,随硬脂酸锌的加入而缩短。Fitzgerald及Weisst结合X-射线小角散射研究了甘油及邻苯二甲酸二辛酯对磺化聚苯乙烯离聚体的动态力学性质的影响。     

Direct analysis of polymer pyrolysis using laser microprobe techniques

A laser microprobe-mass analysis technique has been developed which enables the overall course of polymer decomposition processes to be directly followed. Volatile pyrolysis products evolved during laser-vaporization of the polymer substrate are immediately formed into a molecular beam and mass analyzed. Modulated molecular beam techniques are utilized to provide increased detection sensitivity and to aid in the analysis of complex mass spectra by providing a means to directly discriminate parent ions from fragment ions. Elimination of intermediate product collection stages permits the time-resolved behavior of the polymer decomposition process to be investigated. Results are presented for rigid and plasticized polyvinyl chloride, a polyoxymethylene copolymer and a polyester elastomer block copolymer.     

Encapsulation of β-cyclodextrin by in situ polymerization with vinyl chloride leading to suppressing the migration of endocrine disrupting phthalate plasticizer

We performed the encapsulation of β-cyclodextrin (β-CD) in PVC by in situ polymerization with vinyl chloride monomer (VCM), and investigated the effect of CD encapsulation on the suppression of dioctyl phthalate (DOP) migration suspected as endocrine disruptor. β-CD was partially modified with 3-(methacryloxy)propyl trimethoxysilane and modified β-CD (MCD) was then encapsulated in PVC through suspension polymerization via radical reaction between double bonds MCD and VCM. Resulting MCD-encapsulated PVC (MCD_x-PVC) exhibited the similar morphology and characteristics to commercial PVC. For MCD_x-PVCs plasticized with DOP, they showed the considerably suppressed DOP migration as well as the similar optical and mechanical properties to conventionally plasticized PVC. In particular, the plasticized MCD_x-PVCs exhibited the superior suppression of DOP migration compared to the plasticized PVC where MCD and DOP were introduced by conventional melt mixing. Therefore, the encapsulation of MCD in PVC is thought to be an effective approach to producing the ecological PVC material.     

Properties of poly(vinyl chloride) crosslinked by new difunctional reagents

Alkaline and alkaline earth salts of either dimercaptans obtained by duplication of o-mercaptobenzoic acid with α, ω-diols or of o-mercaptobenzoic acid have been synthesized. Their efficiency has been studied with respect to induction time before change in melt viscosity and crosslinking rate assessed with Haake plasticorder equipped with a Rheomix 600 internal mixer. Then efficiency with respect to crosslinking was also characterized by the assessment of the insoluble fraction in tetrahydrofuran. Mechanical properties of uncrosslinked and crosslinked PVC were compared at different temperature through either static tests with high strain as creep and tensile tests or dynamic test in the elastic domain. Except for creep resistance, crosslinking does not improve mechanical properties of plasticized PVC at temperature lower than 80°C if insoluble fraction in tetrahydrofuran is lower than 100 % by weight. Because chemical crosslinking leads to the existence of two interpenetrated networks, a physical one and a covalent one, the temporary physical network governs the properties until the melting of ordered domains, whereas the covalent network governs the properties if temperature rises above the melting temperature of the crystalline populations. To improve mechanical properties of crosslinked PVC at room temperature, the crosslinking density of the covalent crosslinks must be higher than the density of physical crosslinks. Such a situation is reached if insoluble fraction in tetrahydrofuran becomes 100 % by weight.     

Microphase‐separated structure of telechelic urethane acrylate anionomers and their network in various solvents

Telechelic urethane acrylate anionomer (UAA) chain showed less viscosity and polyelectrolyte behavior in water than dimethyl acetamide (DMAc) because of hydrophobic aggregation. UAA networks prepared in different solvents (water and DMAc) exhibited very different swelling behaviors in the same swelling medium, which can be interpreted as due to the very different microstructures formed in the solvents. UAA networks prepared with water (UAHG networks) had microphase‐separated hydrophilic and hydrophobic domains, whereas UAA networks synthesized with DMAc (UADG networks) had relatively homogeneous network structures. The mechanical property of the UAHG and UADG networks, measured with a dynamic mechanical analyzer, was also very sensitive to the solvent type used during the crosslinking reaction. UAHG networks with a microphase‐separated structure had a higher modulus than UADG networks. The results of the mechanical property measurements showed that water was a much better solvent for the hydrophilic hard segments of UAA chain than DMAc, even though DMAc dissolved both hydrophilic and hydrophobic segments of UAA chain. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2081–2095, 2000