Study of butadiene rubber mastication and mixing with carbon black

A thermomechanical method was applied to study the topological and molecular structure of SKD butadiene rubber masticated and mixed with carbon black. Triblock structure (two amorphous blocks and one a pseudocrystalline structure) of a studied raw rubber and rubber compound networks were found. A ratio of these morphology structures changes during mastication. After mastication, a low‐temperature block has two glass transition temperatures that shows its more complex structure than that in raw rubber. This shows deep transformations taking place during the mastication process. Despite applying high shear forces and heating during mixing with carbon black in a filled BR compound, we present three structures characteristic for BR. However, introduction of carbon black changes the topological structure of polybutadiene. A part of both amorphous blocks grows. A part of a crystalline structure lowers from 88% after 2.5 min of mixing to 54% after 20 min of compounding. The molecular weight distribution of the chains between the junctions of the network and parts of low‐temperature and high‐temperature amorphous blocks, and pseudocrystalline structures in architecture of the rubber network were also calculated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 729–737, 1999     

Structure of natural rubber/emulsion butadiene rubber (NR/EBR) vulcanizates

Diblock amorphous topological structure of a filled vulcanizate network made of natural rubber (NR) and Emulsion Butadiene Rubber (EBR) was found. These blocks differ in the transition temperatures about 200°C. Dual transitions of such rubbers have been assigned as a motion of the mixed soft block [low glass transition temperature (T_g )] in the glassy state and the motion in elements of a network around physical and chemical crosslinking sites in a rigid block (high T_g ), respectively. Compaction of the topological structure of a high‐temperature block during curing (manifested by the growth of T_g ) was noticed. The molecular weight distribution of the chains between the junctions of the network and shares of these amorphous blocks in the structure of the rubber network vs curing time were calculated using the methodology shown. Introduction of Perkalink 900 at constant quantity of sulfur changes a structure of the junctions in the tested rubber network from mixed (10–15% of chemical bonds, and remaining are cluster type and topological junctions) into practically all chemical bonds. Optimal curing time evaluated by the thermomechanical analysis, at which molecular structures formed in both blocks reflect the equilibrium state of adsorption layers of two rubbers introduced into the compound, is close to that evaluated by the vulcametric tests. The location of the molecular weight distribution curve in both blocks one against another depends on rubber formulation. Also, a fact that crosslinks are gathered, as was predicted by Vilgis and Heinrich calculations, was confirmed experimentally. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 732–742, 2000     

Thermomechanical study of butyl rubber mastication during compounding

A thermomechanical method was used to study the topological and molecular structure of model rubber compounds. This structure changes because of mastication during compounding. It was found that raw butyl rubber has a diblock structure. The molecular weight distribution of the chains between the junctions of the polymer network, the coefficient of polydispersity, a share of low-temperature and high-temperature blocks, and changes in their glass transition temperatures as a result of the mixing of butyl rubber depend on both the presence of sulfur and the kind of sulfur (polymeric or mineral). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2159–2167, 1998     

Influence of mixing procedures and curing time on molecular and topological structures of NR/BR vulcanizate

A rubber compound containing butadiene rubber (BR), natural rubber (NR), and carbon black was investigated by thermomechanical analysis (TMA). A difference in dynamics of the formation of molecular and topological structures of a vulcanizate were found to be dependent on the mixing technology and curing time. Separation of the topological structure of cured rubber into two blocks with differing transition temperatures was visible after 20 min of vulcanization, when a share of a low‐temperature block is minimal and M̄_n(n) reaches a stable value of about 2400. A low‐temperature block had a predominant concentration of covalent branching junctions, independent of the mixing procedures, whereas the high‐temperature block had covalent and topological junctions in concentrations that were dependent on the mixing method. For curing times longer than 20 min, the characteristic changes in values of M̄_n(n) are dependent on the procedure of rubber compound mixing. After additional homogenization of compounds and vulcanization, the rubbers are characterized by a diblock structure with the same qualitative structure of the branching junctions as for nonhomogenized ones. In some cases, the homogenization increases the relative concentration of the covalent junctions in the high‐temperature block. When a preblend of BR and carbon black was prepared first, and then mixed with NR, this technology makes rubber compounds less sensitive to additional homogenization during further processing. A mechanism of creation and transformation of rubber–carbon black junctions during compounding and vulcanization of rubber compounds with two raw rubbers that differed in adsorption ability was proposed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 660–669, 2000     

Structure development in silica‐filled polyacrylate rubber composites during mixing

The structure of bound rubber in the composites from fumed silica (A200, Nippon Aerosil Co., Japan) and polyethylacrylate rubber (PEA) was studied as a function of mixing temperature. The fraction of bound rubber in the composites increased gradually with increasing the mixing temperature from 80 to 120°C, followed by saturation above 120°C. High‐resolution solid‐state NMR results revealed that there was no chemical bonding between silanol groups and PEA molecules. Scanning electron microscope and optical microscope observation of the composites indicated that, with increasing mixing temperature, the size of agglomerates formed by silica particles decreased. Further, the molecular weight retention of PEA dropped abruptly above 120°C. Dynamic viscoelastic measurements of the composites suggest that the development of network structure in the composites was greatly affected by the mixing temperature. Based on these data, structure development in composites is discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2529–2538, 1999     

Synthesis of PLLA‐PEOMA comb‐block‐comb type molecular brushes based on AGET ATRP and ring‐opening polymerization

BACKGROUND: Molecular brushes are types of macromolecules with densely grafted side chains on a linear backbone. The synthesis of macromolecular brushes has stimulated much interest due to their great potential in applications in various fields. Poly(L ‐lactide)–poly(ethylene glycol) methyl ether methacrylate (PLLA‐PEOMA) comb‐block‐comb molecular brushes with controlled molecular weights and narrow molecular weight distributions were successfully synthesized based on a combination of activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) and ring‐opening polymerization. The synthetic route is a combination of the ‘grafting through’ method for AGET ATRP of the PEOMA comb block and the ‘grafting from’ method for the synthesis of the PLLA comb block. Poly(2‐hydroxyethyl methacrylate) (PHEMA) was synthesized by ATRP, and PLLA side chains and PEOMA side chains were grown from the backbones and the terminal sites of PHEMA, respectively. RESULTS: The number‐average degrees of polymerization of PLLA chains and poly[poly(ethylene glycol) methyl ether methacrylate] (PPEOMA) comb blocks were determined using ¹H NMR spectroscopy, and the apparent molecular weights and molecular weight distributions of the brush molecules were measured using gel permeation chromatography. The crystallization of the components in the comb‐block‐comb copolymers was also investigated. The crystallization of PLLA side chains is influenced by PLLA chain length and the content of PPEOMA in the molecular brushes. The comb‐block‐comb copolymer composed of hydrophobic PLLA and hydrophilic PEOMA can self‐assemble into a micellar structure in aqueous solution. CONCLUSION: A combination of AGET ATRP and ring‐opening polymerization is an efficient method to prepare well‐defined comb‐block‐comb molecular brushes. The physical properties of the molecular brushes are closely related to their structures. Copyright © 2009 Society of Chemical Industry     

A study on the rheological properties and processability of polycarbonate

The transport theory for the solids conveying zone in a single‐screw extruder was applied to calculate the pressure distributions along the screw channel for several bisphenol A polycarbonate resins based on the screw revolution speed and the flow rate. The pressure distributions and the flow rates of the resins were related to the structural and rheological properties. When polymers have the same chemical structure and number‐average molecular weight and the same mechanical properties, the polymer having a broader molecular weight distribution showed a lower glass transition temperature. For the polymer with broader MWD a relatively low pressure was developed along the screw channel, and an increased flow rate was observed. A relatively short melting length was also observed for this polymer and, accordingly, it was concluded that the polymer with a broader MWD has a better processability. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2921–2929, 2002     

Influence of temperature,molecular weight,and polydispersity of polystyrene on interfacial tension between low‐density polyethylene and polystyrene

In this work, the influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low‐density polyethylene (LDPE) and polystyrene (PS) was evaluated using the pendant drop method. It was shown that interfacial tension between LDPE and PS decreases with increasing temperature for all LDPE–PS pairs studied. The temperature coefficient (∂γ/∂T) (where λ is interfacial tension and T is temperature) was higher for lower molecular weight and larger polydispersity of PS. The interfacial tension between LDPE and PS at a temperature of 202°C increased when the molecular weight of polystyrene was varied from 13,000 to 30,000. When the molecular weight of PS was further increased, the interfacial tension was shown to level off. The effect of polydispersity on interfacial tension between PS and LDPE, at a temperature of 202°C, was studied using PS with a constant‐number average molecular weight and varying polydispersity. The interfacial tension was shown to decrease with increasing polydispersity. However, the influence of polydispersity was lower for PS of higher molecular weight. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2423–2431, 1999     

Detecting structural orientation in isoprene rubber/multiwall carbon nanotube nanocomposites at different scales during uniaxial deformation

Enhanced strain‐induced crystallization (SIC) behavior in isoprene rubber/multiwall carbon nanotube (IR/MWCNT) nanocomposites was analyzed in terms of structural orientation during uniaxial deformation. In situ synchrotron wide‐angle X‐ray diffraction and small‐angle X‐ray scattering (SAXS) reveal the molecular orientation in IR/MWCNT composites at different scales. The inclusion of MWCNTs leads to a decrease in the molecular orientation at small strain due to the promotion of SIC. Meanwhile, the presence of MWCNTs induces a large‐scale orientation within the vulcanized rubber network based on SAXS results. Considering the heterogeneous nature of the vulcanized network, the nucleation process during SIC is discussed from the viewpoint of thermodynamics. The oriented large‐scale structure in IR/MWCNT composites is composed of local rubber chains stretched up MWCNTs, from which the additional nuclei are induced. By forming a bound rubber layer around MWCNTs through attractive interactions, MWCNTs can amplify the local strain of rubber segments and form a highly oriented large‐scale structure, but without altering the overall molecular orientation level. The evolution of detailed structural orientation in MWCNT‐filled rubber composites during deformation is revealed for the first time. © 2017 Society of Chemical Industry     

The effect of polydispersity on structure of ultrasonically treated rubbers

Structure of ultrasonically treated rubbers, as recently shown by us, can be analyzed using the classical theory of rubber network statistics. This theory allows one to calculate gel fraction and crosslink density of a rubber network, provided, in particular, that molecular weight distribution (MWD) of the rubber chains is given. In previous studies, the initial MWD of ultrasonically treated rubbers was assumed to be of Flory's type in order to facilitate calculations. The present paper demonstrates that shape of the initial MWD insignificantly affects calculations of gel fraction and crosslink density if rubber network degradation proceeds through random scissions of main chains and crosslinks as in the case of continuous (with flow) ultrasonic treatment. MWD has been demonstrated to affect kinetics of rubber network degradation if a partial depolymerization of broken chains (thermal degradation) takes place during the ultrasonic treatment, which might happen under the static (no flow) conditions of treatment. The results of illustrative calculations are presented on structure of ultrasonically treated unfilled styrene-butadiene rubber.     

Network topology and the theory of rubber elasticity

The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters.     

Influence of comonomer distribution on crystallization kinetics and performance of polyethylene of raised temperature resistance

Three polyethylene of raised temperature resistance (PE‐RT) materials have been used to explore the factors that cause the differences in crystallization kinetics and mechanical performance between different classes and between the same classes. 1‐PE‐RT and 3‐PE‐RT belong to the same class (type II) but with different comonomer, while 2‐PE‐RT (type I) and 3‐PE‐RT use the same comonomer. The results of tensile and bending tests and isothermal crystallization indicate that different classes or even the same classes of PE‐RT have differences in high‐temperature resistance and long‐term performance. Characterization of the molecular chain structure shows that the comonomer content within the high molecular weight chains is significantly higher than that within the low molecular weight chains, and the comonomer is not uniformly distributed over the short‐chain molecules, which makes 1‐PE‐RT have higher modulus and better long‐term performance. Because the difference of comonomer content in long‐chain molecules and short‐chain molecules is small and the comonomer is relatively uniformly distributed over the short‐chain molecules, 3‐PE‐RT cannot balance the stiffness and the long‐term performance very well. For 2‐PE‐RT, the comonomer content in the long‐chain molecules and the short‐chain molecules is approximately the same and there is no intramolecular comonomer distribution, and thus it has the best long‐term performance but the lowest modulus. 2‐PE‐RT cannot have rigidity and good long‐term performance at the same time. © 2019 Society of Chemical Industry     

Blends of polycarbonate and polysulphone–polydimethyl–siloxane block copolymers: analysis of compatibility and impact strength

The possibility of modifying polycarbonates by using dian (Bisphenol A) polysulphone–polydimethyl siloxane block copolymers having multiblock structure and triblocks with end polydimethyl siloxane or a polysulphone block structure was shown. In triblock copolymers the polydimethyl siloxane blocks have a constant molecular weight equal to 2500, while in polyblocks it was assumed to be 2500 and 10,000. The molecular weight of polysulphone blocks varied between 700 and 9000 in triblocks or between 500 and 4500 in polyblocks. It was found that block copolymers of both multi- and triblock structure with polydimethyl siloxane end blocks of concentration 45–68 wt % are created with PC microheterogenous blends. These blends, in a wide temperature interval (from cryogenic to the glass transition temperature of PC), have high impact strength when multiple crazes are created independently on testing temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1823–1834, 1999     

微观结构对天然橡胶的性能影响研究

研究了各牌号天然橡胶结构,以研究微观结构对天然橡胶各性能的影响。本文采用红外光谱(FTIR)、X射线衍射(XRD)、核磁共振(nmR)、热重分析(TG)等多种手段对泰国产1号烟片、马来西亚产3号烟片、马来西亚产1号烟片和印度尼西亚1号标准胶等四种牌号天然橡胶的微观结构进行了表征,并对各牌号天然橡胶硫化胶进行了一系列测试。实验结果表明:各牌号天然橡胶生胶分子结构相同,均以顺式结构为主。马来西亚产1号烟片和印度尼西亚1号标准胶的结晶程度较好,而泰国产1号烟片具有最高的门尼黏度与黏均分子量。各牌号天然橡胶在空气与氮气中的热稳定性相似。各牌号天然橡胶的门尼黏度大小顺序为:1~#>2~#>3~#>4~#。各牌号天然橡胶的黏均分子量大小顺序为:1~#>4~#>2~#>3~#。各牌号天然橡胶在空气中分三阶段进行热分解,而在氮气中的热分解仅为一阶段。各胶料在空气与氮气中的热稳定性大体相同。     

Structure and deformation of an elastomeric propylene–ethylene copolymer

The elastic behavior of a propylene–ethylene copolymer was investigated. An initial “conditioning” tensile extension up to 800% strain resulted in an elastomer with low initial modulus, strong strain hardening, and complete recovery over many cycles. Structural changes that occurred in the low crystallinity propylene–ethylene copolymer during conditioning, and that subsequently imparted elastomeric properties to the conditioned material, were investigated. Thermal analysis, wide and small angle X‐ray diffraction, and atomic force microscopy measurements were performed at various strains during the conditioning process. Conditioning transformed crystalline lamellae into shish‐kebab fibers by melting and recrystallization. The fibers, accounting for only 5% of the bulk, were interconnected by a matrix of entangled, amorphous chains that constituted the remaining 95%. It was proposed that the shish‐kebab fibers acted as a scaffold to anchor the amorphous rubbery network. Entanglements of the amorphous chain segments acted as network junctions and provided the elastic response. The stress–strain response of materials conditioned to 400% strain or more was described by the classical rubber theory with strain hardening. The extracted value of M_c, the molecular weight between network junctions, was intermediate between the entanglement molecular weights of polypropylene and polyethylene. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 489–499, 2007     

Peroxide crosslinking of a styrene‐free unsaturated polyester

Thermoset unsaturated polyesters are usually obtained by the crosslinking of unsaturated polyester chains dissolved in an unsaturated, reactive, monomeric diluent, which is usually styrene. This article describes a new approach in which styrene‐free unsaturated polyester chains are intrinsically cured into a crosslinked matrix. The gel time, gel content, swelling degree, glass‐transition temperature, dynamic mechanical properties, tensile properties, and molecular weight between crosslinks (calculated according to both the Flory–Rehner equation and the theory of rubber elasticity) of the crosslinked polymer are studied as a function of the peroxide concentration. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2 wt %) and change to a lesser extent with higher peroxide concentrations (up to 6 wt %). The thermal properties of the isolated gel fraction are studied as a function of the peroxide concentration. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the glass‐transition temperature and stress–strain behavior of the crosslinked polymer. In light of the crosslink densities derived from swelling experiments, a molecular structure and crosslinking mechanism are suggested for the gel fractions of 1 and 6 wt % peroxide crosslinked unsaturated polyester chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Melt rheology of segmented polyamides: Effect of block molecular weight

Segmented polyamides, also known as polyether‐ester‐amides, are composed of polyether and polyamide structural units. The rheological behavior of segmented polyamides with respect to the variations in the molecular weight of hard and soft blocks has been studied using a Monsanto Processability Tester. These systems exhibit pseudoplastic flow behavior. The shear viscosity of the segmented polyamides decreases with a decrease in hard block molecular weight up to 1500. However, at low shear rates, the shear viscosity shows marginal change with an increase in soft segment molecular weight. The equilibrium die swell increases with an increase in shear rate, but decreases with increasing temperature. The stress relaxation study of the segmented polyamides reveals that the stress developed during extrusion relaxes exponentially for all the systems. The equilibrium die swell at a fixed temperature and shear rate, the time required to relax a fixed amount of stress and the stress developed after a certain time interval decrease with a decrease in hard block molecular weight up to 1500, but increase with an increase in soft segment molecular weight. The activation energy of the melt flow process increases with the rate of shear in most of the cases. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1739–1747, 1999     

Average Molecule Construction of Petroleum Fractions Based on 1H-NMR

The calculation of chemical structures and physical properties is the basis of petroleum refining optimization. In this article, a method to build an average molecule model for hydrocarbons and petroleum fractions is developed. ¹H-NMR, molecular weight, and elemental composition were used as input parameters to construct a single molecular model that represents the average chemical structure. The average molecules were constructed by assembling the average building blocks, which are a set of predefined structural fragments, covering typical hydrocarbon and heteroatom functional groups in petroleum systems. After applying a group contribution method to the derived molecule, the bulk property of a sample could be directly calculated. The method was validated by being applied to various model compounds (including paraffins, cycloalkanes, aromatics, and heteroatom-containing species), where it successfully predicted the average building blocks, unit sheets number, and physical properties. The application of this method to petroleum fractions was demonstrated. © 2018 American Institute of Chemical Engineers AIChE J, 65: 270–280, 2019     

Dynamic response of transiently trapped entanglements in polymer networks

The structure and viscoelastic response of polymer networks are highly sensitive to the presence of pendant chains. These imperfections, that are unavoidable produced during a cross-linking reaction, reduce the cross-linking density and affect the damping response of elastomers. In this work the dynamics of pendant chains present in a cross-linked network is investigated using end-linked poly(dimethyl-siloxane) networks with well defined structure. For this purpose, model networks containing 10 and 20 wt% of two different monodisperse pendant chains with molecular weights well above the critical entanglement molecular weight and some of their blends were prepared. It was found that, within this range of concentration of pendant chains, the long-time dynamic response of the networks was nearly insensitive to the content of pendant material but deeply influenced by the average molar mass of these defects. While the equilibrium behavior of the networks can be well described by a mean field theory for rubber elasticity, the long time relaxational dynamics can be rationalized in terms of the Pearson-Helfand picture for the arm retraction process. Within this theoretical picture, the dynamics can be explained in terms of the molecular architecture of the network, the Rouse time and the weight average molar mass of the pendant material.     

Influence of the final extent of reaction on the structure of model polydimethylsiloxane networks obtained by the end-linking hydrosilation reaction

Summary Model silicone networks obtained by hydrosilation of vinyl terminated polydimethylsiloxane chains have been used extensively to verify molecular theories of rubber elasticity. In these networks, the maximum extent of reaction obtained during cross linking considerably affects their final structure. The degree of completion of the hydrosilation reaction depends on the concentration of reactive groups. A recursive approach and kinetic data from the literature are used to show that, for this particular reaction, perfect networks, i.e. those with high concentration of elastically active network chains, are only obtained when a relatively high concentration of reactive groups is present in the system. This critical concentration corresponds in a bulk reaction to polydimethylsiloxane chains with a number average molecular weight lower than 10,000.