Effect of the modification of silica on thermal properties and flammability of cross-linked butadiene-acrylonitrile rubbers

The paper presents the results of testing the thermal stability and flammability of butadiene-acrylonitrile rubber vulcanizates with different contents of combined acrylonitrile: Perbunan NT 1845 and Perbunan NT 3945 from Bayer, containing unmodified and bromine- or iodine-modified silica. The test results were obtained with the use of a derivatograph, measurements of flammability by the method of oxygen index, in air and also with the use of a cone calorimeter. The effect of the modification on the zeta potential was also examined. A considerable reduction in the flammability of nitrile rubber vulcanizates filled with silica can be obtained by the modification of filler with bromine or iodine. All the vulcanizates containing modified silica are self-extinguishing. An appropriate filling of NBR 39 vulcanizates with bromine-modified silica makes it possible to obtain non-flammable polymeric materials. They neither ignite nor glow under the action of a flame source for 30 s. The findings can be a rational basis for the synthesis of modified silica that can act as active filler and effective flame-retardant agent at the same time.     

Polysiloxane dizwitterionomers. V. Microstructure and mechanical properties

The mechanical properties of the polysiloxane dizwitterionomers change dramatically with a tenfold increase in the ionic content, from soft, weak materials to hard, strong rubbers. The effects of the zwitterion concentration and the unique morphology on the elastic modulus can be explained by treating this series of ionomers as composites. Macro- and microfibrillation were observed in 1- and 2-mole % zwitterion samples before the ultimate break and are probably due to reorientation of the ionic domains parallel to the stress direction so that cracks could propagate in the direction of the stress.     

Dynamic mechanical properties and thermal degradation process of the compositions obtainedfrom unsaturated poly(ester urethanes) cross-linked with styrene

Dynamic mechanical and thermal properties of poly(ester urethanes) (PEU) cross-linked with styrene have been studied. The investigated polyurethanes were obtained from 4,4′-diphenylmethane diisocyanate and unsaturated oligo(alkyleneester)diol based on cis-2-butene-1,4-diol. The conducted analyses dealt with the correlation between the chemical structure of poly(ester urethanes) and their ability to phase separate as well as their thermal stability. The products of PEU thermal degradation were characterized using infrared spectroscopy.     

Shape memory and mechanical properties of cross-linked polyethylene/clay nanocomposites

Shape memory polymer (SMP) such as cross-linked low-density polyethylene (XLDPE), can return from its temporary shape to the original (permanent) shape upon heating. SMP in comparison with shape memory alloy (SMA) and shape memory ceramic (SMC) has lower stiffness, so generates lower recovery force when it is being used as an actuator. Also, when SMP is reinforced with traditional micro-fillers, it often loses its shape memory effect due to the high weight fraction of filler (20-30%). To overcome these disadvantages, nanoclays can be used. The smart resultant nanocomposite, even in small clay loading level (0-10 wt.%), shows higher modulus, strength, and the other physical properties such as higher recovery force, required to act as an actuator.In this work, the effect of modified montmorillonite on mechanical and shape memory properties as well as the force generation of a shape memory cross-linked low density polyethylene were investigated.The results show that the modulus of elasticity, the recovery temperature, the recovery force and force recovery rate increase with increasing organoclay in nanocomposites, but final recovery strain decreases slightly.     

Dynamic mechanical and crystal-strain measurements on ultrahigh modulus oriented polyoxymethylene: A revised value for the true crystal modulus

Dynamic mechanical measurements on ultrahigh modulus polyoxymethylene have been undertaken over the temperature range ?150 to 20°C. Measurements of the longitudinal crystal modulus have also been made by studying changes in the (009) reflection with load, over a similar range of temperatures. The dynamic Young's modulus at 5 Hz reaches a value at low temperatures of 64.5 GPa for the most highly oriented sample. The crystal modulus at low temperatures is 105 GPa, which is almost twice the previously reported room-temperature value.     

Relationship between swelling and mechanical properties of cross-linked polymers mixed with sand

Cross-linked polymers consisting of acrylamide, sodium acrylate, starch fragments and a cross-linker were synthesized with the same content of carboxyl groups and three degrees of cross-linking Q of 0.04, 0.2 and 1 wt%. An increase in Q gradually reduces the swelling of polymer gels in water; when distributed in sand, polymer gels exhibit maximum swelling at Q = 0.2 wt%. It is shown that the behavior of polymer gels in sand is determined by the balance between the elasticity of swollen polymer gels and the resistance of sand particles     

Hybrid copolymer latexes cross-linked with methacryloxy propyl trimethoxy silane. Film formation and mechanical properties

We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (MPS) with styrene (Styr.) and n-butyl acrylate (BuA) monomers through emulsion polymerization. The so-produced hybrid copolymer (P(BuA-co-MPS)) and terpolymer (P(Styr-co-BuA-co-MPS)) latexes were cast into films that displayed a good optical transparency. The copolymers microstructure in the films was characterized by FTIR, ¹³C and ²⁹Si solid state NMR spectroscopies, and was found to be highly dependent on parameters such as the monomer feed composition, the suspension pH and the silane addition profile. The films obtained from the hybrid latexes showed improved dynamic mechanical properties indicating that a reinforcing organo-mineral network had formed in the composite materials. The dynamic modulus of the hybrids increased with increasing silane contents while, concurrently, the tan δ peak shifted to higher temperatures, broadened and decreased in intensity. To cite this article: S. Vitry et al., C. R. Chimie 6 (2003).     

Small-molecule dynamics and mechanisms underlying the macroscopic mechanical properties of coordinatively cross-linked polymer networks

Specific metal-ligand coordination between bis-Pd(II) and Pt(II) organometallic cross-linkers and poly(4-vinylpyridine) in DMSO defines a three-dimensional associative polymer network. Frequency-dependent dynamic mechanical moduli of a series of four different bulk materials, measured across several decades of oscillatory strain rates, are found to be quantitatively related through the pyridine exchange rates measured on model Pd(II) and Pt(II) complexes. Importantly, the mechanism of ligand exchange in the networks is found to be the same solvent-assisted pathway observed in the model complexes, and so the bulk mechanical properties are determined by relaxations that occur when the cross-links are dissociated from the polymer backbone. It is how often the cross-links dissociate, independently of how long they remain dissociated, that determines the bulk mechanical properties. The quantitative relationship between bulk materials properties and the kinetics and mechanisms observed in model compounds holds promise for the rational, molecular design of materials with tailored mechanical properties.     

Thermal and dynamic mechanical analysis of cross-linked poly(esterurethanes)

New cross-linked poly(esterurethanes) (PEU) based on unsaturated olygo(alkyleneester)diol (OAE), 4,4’-diphenylmethane diisocyanate (MDI) and styrene or methyl methacrylate as curing monomers were prepared. The synthesis of PEU was performed in two steps. In the first step OAE was obtained from adipic acid, maleic anhydride and ethylene glycol. In the second step a prepolymer was obtained in a reaction of OAE with different amounts of 4,4’-diphenylmethane diisocyanate followed by crosslinking using previously mentioned curing monomers. The influence of structure of the poly(esterurethanes) on thermal and dynamic mechanical properties is studied. Thermogravimetric analysis shows that cross-linked poly(esterurethanes) demonstrate high thermal stability. Moreover the dynamic mechanical thermal analysis shows that the presence of styrene cross-linking chains in polymers lead to the phase separation in cross-linked poly(esterurethanes).     

Synthesis and dynamic mechanical properties of cross-linked multiblock poly(urethane-imide) copolymers

Russian Chemical Bulletin - Poly(urethane-imide) copolymers (PUICs) containing reactive carboxyl groups in hard imide segment were synthesized from poly(propylene glycol) with isocyanate end...     

Physical properties and structure of silk. II. Dynamic mechanical and dielectric properties of silk fibroin

Dynamic mechanical and dielectric properties of amorphous regenerated films of silk fibroin were studied as a function of temperature. A mechanical loss tangent peak at about 175°C may be due to the segmental motion of the main chains in the amorphous silk fibroin film. The dynamic modulus of the amorphous silk fibroin increased at 185°C due to the crystallization of the silk fibroin. Dielectric loss tangent peaks were observed at about ?40°C and 175°C at 1 kHz. The former is ascribed to the local motion of the amorphous silk fibroin with absorbed water, while the latter seems to originate from the segmental motion of the main chains and the crystallization of silk fibroin.     

Extracting uncrosslinked material from low modulus sylgard 184 and the effect on mechanical properties

Commercial silicone elastomers are commonly used in soft materials research due to their easily tunable mechanical properties. However, conventional polydimethylsiloxane (PDMS) elastomers with moduli below ∼100 kPa contain uncrosslinked free molecules, which play a significant role in their behavior. To utilize these materials, it is important to quantify what role these free molecules play in the mechanical response before and after their removal. We present a simple and inexpensive extraction method that enables the removal of free molecules from a lightly crosslinked sheet of Sylgard 184, a commercially available PDMS elastomer. The materials can contain a majority of free molecules yet maintain a thin and flat geometry without fractures after extraction. Subsequently, we compare the modulus, maximum stretchability, and hysteresis behavior with mixing ratios ranging from 60:1 to 30:1, before and after extraction. We show that the modulus, maximum stretchability, and dissipation increase upon extraction. Moreover, our approach offers a route to prepare crosslinked silicone elastomers with a modulus as low as ∼20 kPa without free molecules from a commercially available kit. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 343–351     

Dynamic mechanical properties of plasticized polystyrene-based ionomers. II. Melt rheology

A high molecular weight styrene ionomer containing 5 mol% sodium methacrylate was blended with a styrene oligomer (MW 800) and investigated by dynamic mechanical techniques. The focus of the study is on the dynamic melt rheology of these materials, whose ratios by weight of ionomer to oligomer are 60/40, 40/60, and 25/75. The glass-transition temperature and ionic transition are first characterized by torsion pendulum measurements as a function of temperature. It appears that a maximum level of plasticization is achieved for the ionic regions, the extent depending on sample history. Time–temperature superposition is obeyed by the blend of 60 wt% ionomer, but not by the other two blends. Relaxations due to the ionic regions are clearly evident in the relaxation spectra of all three blends. Above a particular temperature, the 25 wt% blend indicates an Arrhenius type of dependence.     

Organic hybrid of chlorinated polyethylene and hindered phenol. I. Dynamic mechanical properties

Dynamic mechanical properties and microstructure of an organic hybrid consisting of chlorinated polyethylene (CPE) and 3,9‐bis[1,1‐dimethyl‐2{β‐(3‐tert‐butyl4‐hydroxy‐5‐methylphenyl)propionyloxy}ethyl]‐2,4,8,10‐tetraoxaspiro[5,5]‐undecane (AO‐80) were investigated. The AO‐80 clearly exhibited two second‐order transitions at 6 and 69 °C in addition to the melting: the transition at lower temperature is assigned to the glass transition, and the transition at higher temperature is considered to be caused by the dissociation of hydrogen bond between the hydroxyl groups of AO‐80. When blending with CPE, part of AO‐80 molecules was dispersed into the CPE matrix, and most of them formed an AO‐80‐rich phase. As a result, a novel transition appeared above the glass‐transition temperature of the CPE matrix. It was assigned to the dissociation of the intermolecular hydrogen bond between the α‐hydrogen of CPE and the hydroxyl groups of AO‐80 within the AO‐80‐rich phase. Dynamic mechanical properties and microstructure of CPE/AO‐80 hybrid were controlled by the thermal treatment. It was found that the CPE/AO‐80 hybrid is a good damping material and shows a shape memory effect. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2285–2295, 2000     

Characterization of the mechanical properties of cross-linked serum albumin microcapsules: effect of size and protein concentration

A microfluidic technique is used to characterize the mechanical behavior of capsules that are produced in a two-step process: first, an emulsification step to form droplets, followed by a cross-linking step to encapsulate the droplets within a thin membrane composed of cross-linked proteins. The objective is to study the influence of the capsule size and protein concentration on the membrane mechanical properties. The microcapsules are fabricated by cross-linking of human serum albumin (HSA) with concentrations from 15 to 35 % (w/v). A wide range of capsule radii (～40–450 μm) is obtained by varying the stirring speed in the emulsification step. For each stirring speed, a low threshold value in protein concentration is found, below which no coherent capsules could be produced. The smaller the stirring speed, the lower the concentration can be. Increasing the concentration from the threshold value and considering capsules of a given size, we show that the surface shear modulus of the membrane increases with the concentration following a sigmoidal curve. The increase in mechanical resistance reveals a higher degree of cross-linking in the membrane. Varying the stirring speed, we find that the surface shear modulus strongly increases with the capsule radius: its increase is two orders of magnitude larger than the increase in size for the capsules under consideration. It demonstrates that the cross-linking reaction is a function of the emulsion size distribution and that capsules produced in batch through emulsification processes inherently have a distribution in mechanical resistance.     

Changes in the static and dynamic mechanical moduli of rubbers during ageing

Changes in the static and dynamic mechanical (complex) moduli for TMTD (filled and unfilled) and S/CBS-vulcanised (unfilled) natural rubber cylinders (height = diameter = 20 mm) were intermittently recorded as a function of time up to 1000 h at different temperatures. For the TMTD-vulcanisates, the moduli decreased with time of ageing and for the S/CBS-vulcanisate a maximum was obtained. The phase angle between stress and strain increased with increasing temperature and with time of ageing. The changes in moduli were attributed to scission and crosslinking reactions. The unfilled TMTD-vulcanisate showed no dependence on dynamic amplitude, whereas the S/CBS-vulcanisate showed a strong dependence on dynamic mechanical amplitude for ageing times longer than 300 h. Whhen log₁₀ (tan δ)_was plotted against 1/T, a straight line was obtained for temperatures between 75 and 150°C. An activation energy of 25 kJ/mole was obtained. This value is in agreement with the activation energy for the diffusion of oxygen in natural rubber.     

Comparative study of pineapple leaf microfiber and aramid fiber reinforced natural rubbers using dynamic mechanical analysis

Natural fiber is often considered inadequate for high performance reinforcement of polymer matrix composites. However, some natural fibers have relatively high mechanical properties with modulus close to that of high-performance synthetic fibers. Since the reinforcing efficiency of a short fiber is determined not only by the fiber modulus, but also by other physical properties such as the length to diameter ratio. Here it is shown, for the first time, that pineapple leaf fiber, whose modulus is somewhat lower than that of aramid fiber, can be used to reinforce natural rubber more effectively than aramid fiber. The situation was achieved by breaking down the fiber bundles into the constituent microfibers to gain very high aspect ratio. Comparisons were made at fiber contents of 2, 5 and 10 parts (by weight) per hundred of rubber (phr) using dynamic mechanical analysis over a range of temperature. The results reveals that at temperature below the glass transition of the matrix rubber and low fiber contents of 2 and 5 phrs, aramid fiber displays slightly better reinforcement efficiency. At high temperatures of 25 and 60 °C and high fiber content of 10 phr, pineapple leaf microfiber clearly displays higher reinforcement efficiency than does aramid fiber. Surface modification of the fiber by silane treatment provides a slight improvement in reinforcing efficiency.     

Preparation and properties of physically and chemically cross-linked hybrid hydrophobic association hydrogels with good mechanical strength

To correct the defects of hydrophobic association hydrogels(HA-gels), new physically and chemically cross-linked hybrid hydrophobic association hydrogels(hybrid HA-gels) were prepared by radical copolymerization of acrylamide(AM), octylphenol polyoxyethylene(n) acrylate(OPn AC, n stands for the number of ethoxy group, and is 10 and 21) and N,N′-methylenebisacrylamide(MBA). On the basis of the statistical molecular theory of rubber elastic, the Mooney-Rivlin model and using the tensile true stress(σ_true) tested at room temperature, the number of network strands per unit volume(υ_0) and the number-average molar mass of a network strand(M_c) were evaluated for hybrid HA-gels. For the hydrogels, the effect of the content of MBA and OP10 AC on their tensile mechanical properties was studied by using υ_0 and M_c; also, the effect of the compositions and temperature on their swelling behavior in distilled water was discussed in detail. In addition, hybrid HA-gels including a small quantity of MBA possessed the capabilities of secondary self-healing and remolding. In contrast with HA-gels prepared by the same compositions besides MBA, hybrid HA-gels showed good mechanical strength and long-term thermal stability in distilled water in the range of 25 to 80 °C. Furthermore, hybrid HA-gels also avoided the self-deswelling behavior of HA-gels. The results show that the application fields of HA-gels will be greatly broadened after introducing a chemical cross-linking network.     

Dynamic mechanical properties of plasticized polystyrene-based ionomers. I. Glassy to rubbery zones

The plasticizing effect of a nonpolar and a polar diluent in ionomers was studied by dynamic mechanical methods in the glassy to rubbery regions. Specifically, a carboxylate and a sulfonate polystyrene-based ionomer were investigated with variation of diethylbenzene content and of glycerol content. It was found that the nonpolar diluent plasticizes the transition by formation of ionic aggregates as well as lowering the glass transition temperature. However, the ionic regions of the carboxylate ionomer are plasticized more than those of the sulfonate ionomer. This corroborates the results of other studies which had found that the sulfonate groups in ionomers interact more strongly than the carboxylate groups. The polar diluent causes the ionic transition to disappear; this is probably due to solvation of the ions by the diluent.