Effect of mineral fillers on thermal properties and flammability ofcis-1,4-polyisoprene vulcanizates

The effect of mineral fillers such as Ultrasil VN-3, Ze?O?Sil P-45, Aerosil 200, Frantex 8, Kaolin and precipitated calcium carbonate on the thermal properties sulphur vulcanizates ofcis-1,4-polyisoprene were studied by means of thermal analysis. It was found that the addition of a mineral filler did not change the nature of the thermal processes in isoprene vulcanizates essentially, but it distinctly affected the positions of the peaks recorded in the DTA curves. The mineral fillers affected the temperatures and rates of degradation and destruction of polyisoprene cross-linked with sulphur. The presence of a mineral filler brought about a decrease in the flammability ofcis-1,4-polyisoprene sulphur vulcanizates.     

Processability characteristics and physico-mechanical properties of natural rubber modified with cashewnut shell liquid and cashewnut shell liquid-formaldehyde resin

Natural rubber (NR) has been modified with 5-15 phr each of cashewnut shell liquid (CNSL) and cashewnut shell liquid-formaldehyde (CNSLF) resin with a view to studying the processability characteristics of the mixes and physicomechanical properties of their vulcanizates. The plasticizing effect of these additives in NR was shown by the reduction in melt viscosity and power consumption during mixing in a Brabender Plasticorder compared to that of unmodified NR. Despite the reduction in chemical crosslink density, the vulcanizates containing 15 phr of CNSL and 5-10 phr of CNSLF showed higher tensile and tear strengths and elongation at break. The higher values of activation energy for thermal decomposition of the vulcanizates containing 15 phr each of CNSL (301 kJ/mol) and CNSLF (372 kJ/mol) than that of the unmodified NR vulcanizate (177 kJ/mol) indicate improvement in thermal stability of NR vulcanizates in presence of the modifiers.     

Sulfur-Free Vulcanization of Modified Butadiene-Acrylonitrile Rubber SKN-40PVKh-30, Aimed To Obtain Elastomeric Materials Resistant to Aggressive Media

A study was made of the thermal, peroxide, and radiation vulcanization of modified butadiene-acrylonitrile rubber SKN-40PVKh-30 in the presence of a polyhalomethyl compound, 1,4-bis[(4-trichloromethylphenyl)dichloromethyl]benzene, with epoxy and phenol-formaldehyde resins and 4,4′-dithiobis-N-phenylmaleimide (a sensitizer) additionally included in the formulation with the aim to improve the technical properties of the vulcanizates and elastomeric materials. The parameters of the three-dimensional network of the vulcanizates were studied by sol-gel analysis; the total number of active chains of the network (1/M_c), number of cross-linked molecules \((1/M_{n_\tau } )\), and gel fraction content were determined for the thermal, peroxide, radiation, and thermoradiation vulcanizates.     

Rheological properties of ethylene-propylene-diene elastomers

The processing of rubbers comprises a combination of complicated processes which realization almost always requires knowledge of their rheological behavior. The goal of the present work is to describe the rheological behavior of the EPDM vulcanizates via rotational rheometry. The effect of the cross-linking density and plasticizer content on the rheological behavior of the EPDM vulcanizates is described. The viscoelastic characteristics of the samples are defined from the frequency dependences of elasticity modulus G' and loss modulus G".     

Synthesis and Antioxidative Properties of Bis(3,5-di-tert-butyl-4-hydroxyphenyl) Polysulfides

An efficient procedure was developed for preparing bis(3,5-di-tert-butyl-4-hydroxyphenyl) polysulfides in the presence of phenolic Mannich bases. The antioxidative activity of the resulting bis(polysulfides) in rubbers of various structures and in their vulcanizates was examined.     

高疲劳寿命氯丁橡胶基减振材料的结构与性能

以氯丁橡胶(CR)为基体材料, 将新型反式-1,4-丁二烯-异戊二烯共聚橡胶(TBIR)引入传统CR减振基体中, 探讨TBIR在减振材料中的应用前景. 研究发现, 随着TBIR用量的增加, CR/TBIR混炼胶的强度及模量明显提升; CR/TBIR硫化胶的拉伸强度、 撕裂强度、 压缩永久变形、 动静刚度比及耐疲劳性能均得到改善, 特别是一级疲劳寿命提高了50%~400%(未填充体系)及40%~180%(填充体系), 六级疲劳寿命提高了60%~500%(未填充体系)及30%~120%(填充体系). 与未填充CR/TBIR硫化胶相比, 填充CR/TBIR硫化胶由于炭黑补强作用及填料-聚合物相互作用的引入, 屈挠疲劳寿命、 撕裂强度及拉伸性能均显著提高. 与填充CR硫化胶相比, 填充CR/TBIR质量比为90/10的并用胶能够在保持硫化胶的损耗因子基本不变的基础上, 实现综合性能的平衡提升.     

Fracture morphology and mechanical properties of ethylene/vinyl acetate rubber vulcanizates reinforced by in situ prepared sodium methacrylate

Ethylene/vinyl acetate rubber (EVM) was reinforced by sodium methacrylate (NaMAA) that was in situ prepared through the neutralization of sodium hydroxide and methacrylic acid in EVM during mixing. The mechanical properties of EVM vulcanizates with different NaMAA loadings and at different crosslink densities were studied and compared with those of high abrasion furnace carbon black (HAF) filled EVM vulcanizates. The fracture surfaces of gum and filled EVM vulcanizates were observed with scanning electron microscopy. The results showed that NaMAA‐reinforced EVM vulcanizates had better mechanical properties than HAF/EVM vulcanizates. When the NaMAA loading was 50 phr, the tensile strength of the NaMAA/EVM vulcanizate was 30 MPa, the tear strength was 102 kN/m, and the elongation at break was over 400%. Fourier transform infrared analysis confirmed that NaMAA formed in the compounding process and underwent polymerization during vulcanization. Scanning probe microscopy analysis revealed that nanoscale particles dispersed in the NaMAA/EVM vulcanizates. The mechanical properties were correlated with the fracture morphology of all the vulcanizates. The tensile rupture of NaMAA‐filled EVM vulcanizates occurred through tearing from a crack in the bulk of the samples. Tear deviation occurred with the addition of NaMAA and resulted in a rough surface, leading to an improvement in the tear strength of NaMAA‐filled EVM vulcanizates. The micrographs of the tear surfaces of the vulcanizates indicated that the different fracture modes depended on the NaMAA loading and the crosslink density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1715–1724, 2004     

Stress-induced crystallization and physical properties of trans-polypentenamer

The thermoelastic behaviour of trans-polypentenamer has been investigated by stress-temperature measurements of various samples at different stretching ratios, in order to study its thermodynamic properties and the occurrence of stress-induced crystallization. Different vulcanizates have been examined, both gum and filled; the influence of curing formulation on these properties has been studied. The dependence of melting temperature on the stretching ratio was found to follow Flory's equation up to $\text{α ? 4}$, whereas at a higher extension a different trend occurs in concomitance with the non-Gaussian elastic behaviour. The effect of fillers, both white and black, on the energetic contribution to the retractive force was found to be negligible, when the “strain amplification factor” was used to account for the reinforcement. Finally a comparison has been made between the thermodynamic and the mechanical-dynamical properties of the vulcanizates.     

Vinyl ester resin modified with silicone-based additives: III. Curing kinetics

Silicone-based additives have been used as fire retardants for thermoplastics with the advantageous of improving the processing and the impact resistance of the polymers. In this work the influence of these additives on the curing kinetics of a vinyl ester resin was studied. Three silicone-based additives were used to modify the properties of the vinyl ester resin. The principal differences between them are the functional groups inserted in the polydimethylsiloxane chains. The additives were dispersed in the resin containing a commonly used mixture of initiator and catalyst methylethylKetone peroxide and cobalt-II octanoate, respectively. For some reactional mixtures N,N-dimethylaniline (DMA) was used as promoter. Differential scanning calorimetry (DSC) was used to perform the non-isothermal cure of the non-modified resin and of the resins modified with the additives. Ozawa´s, Kissinger´s and Ozawa´s isoconversional methods were used to determine the kinetic parameters. For resin cured in absence of DMA the silicone-based additives act as retardants for the curing reaction, a typical diluent effect, while in presence of this promoter the reaction enthalpy as well as the reaction rate were improved. This effect was attributed to specific interactions and reactions between DMA and the silicone-based additives that changed the curing mechanism as well as controlled the phase segregation.     

Microbial desulfurization of ground tire rubber by Thiobacillus ferrooxidans

This study focused on the microbial desulfurization of ground tire rubber (GTR) by Thiobacillus ferrooxidans, which selected from the soil of an iron mine had strong sulphur oxidizing capacity. GTR was desulfurizated in the modified Silverman medium during the cultivation of T. ferrooxidans for 30 days, and T. ferrooxidans was able to maintain a high biomass. The continuous increase of SO₄²⁻ in the medium indicated that the sulfur on the surface of GTR was oxidized. FTIR-ATR and XPS spectra revealed that a rupture of conjugated CC bonds and a reduction of sulfur content on the surface of GTR had occurred during desulfurization. The sol fraction of GTR increased from its original 4.69%-7.43%. Compared with GTR sheet, desulfurizated GTR (DGTR) sheets had much smoother surfaces, better physical properties, and higher swelling values. NR vulcanizates filled with DGTR (with 10-40 phr loading) had lower crosslink density and better mechanical properties than those filled with GTR at the same loading. The results determined by DMA suggested that NR vulcanizates filled with DGTR had a reduction of molecular chain friction resistance during glass transition and SEM photograph indicated a better interface coherence between DGTR and NR matrix.     

Interfaces in Composites. Reinforcement of Elastomers by Carbon Black

Basic features of carbon black-aggregation of particles into structure, particle size and morphology, and surface activity-are reviewed. Carbon black reinforcement of vulcanizates is first examined in the example of tearing, and the influence of hysteresis is considered. The dynamic properties of vulcanizates containing two major types of reinforcing carbon black are compared.

While particle size gives the best correlation with tensile strength of vulcanizates, surface activity is shown to be the key to reinforcement. The role of these properties of carbon black in dissipating rupture energy is discussed.

The relation between work to tensile break and hysteresis to break in gum rubbers can be applied to black-reinforced vulcanizates by use of a strain amplification factor. The complication introduced by stress-softening is explained in terms of localized stress relaxation. Abrasion reinforcement can also be explained in terms of hysteresis.

The Flory-Rehner relationship of modulus of elasticity of swollen vulcanizates to physically-effective cross-linking applies to unswollen vulcanizates only after prestressing. Black-reinforced vulcanizates involve application of the strain amplification factor.

The concept of mobile linkages to rubber chains at the surface of black particles is related to the influence of strain magnification and strain rate magnification in the reinforcing mechanism. These linkages result in formation of “shell” rubber adjacent to carbon black particles. The slippage of rubber chains relative to carbon black aggregates allows stress-sharing by highly-stressed chains. Bound rubber results from reaction of elastomer free radicals generated during mastication with carbon black.

There is a relation between bound rubber and reinforcement which is fully developed only after vulcanization. Formation of bound rubber results from the surface activity of carbon black rather than its structure. Its contribution to reinforcement of the vulcanizate may be as important as cross-linking.     

TBIR应用于航空胎侧胶的热氧老化性能

研究了反式-1,4-丁二烯-异戊二烯共聚橡胶(TBIR)应用于航空轮胎胎侧胶[天然橡胶(NR)/顺丁橡胶(BR)/TBIR]的耐热氧老化性能.结果表明,与NR/BR硫化胶相比,10～20份质量的TBIR取代BR后,NR/BR/TBIR硫化胶的交联密度明显提高,压缩温升降低2. 2～3. 4℃,耐屈挠疲劳性能提高约100%,填料分散性改善,填料团聚体体尺寸减小,拉伸性能基本不变.随热氧老化时间延长,硫化胶的交联密度先增加后降低,并用TBIR的硫化胶交联密度在老化48 h后趋于平缓.与NR/BR相比,老化后的NR/BR/TBIR硫化胶生热最低,耐屈挠疲劳性最高.     

Mechanical characteristics of hydrogenated natural rubber vulcanizates

Mechanical properties of partially hydrogenated natural rubber (HNR) vulcanizates were evaluated regarding their chemical structure and crystallizable nature of HNR, and are reported here, to the best of our knowledge, for the first time. HNRs of three levels of hydrogenation (20.6, 29.0, and 40.6 mol%) were successfully prepared by the chemical modification of natural rubber (NR) latex using N₂H₄ and H₂O₂ as reagents, in a sufficient amount for preparing sulfur‐crosslinked samples to be subjected to mechanical and structural measurements. The three HNR vulcanizates were found to be crystallizable upon stretching; it is noted that even 40.6 mol% hydrogenation did not prevent HNR vulcanizates from crystallization upon stretching, while their onset strain of crystallization was higher than that of NR vulcanizate. The hysteresis loss and residual strain up to a stretching ratio of 2 for the HNR vulcanizates tended to become larger with the increase in the degree of the hydrogenation. Tensile and dynamic mechanical properties of 20.6 mol% hydrogenated HNR vulcanizate were comparable to those of NR vulcanizate. From differential scanning calorimetry and temperature dispersion of dynamic modulus or loss, the glass transition temperatures of HNR vulcanizates were found to be almost the same as that of NR vulcanizate, which is also notable. The thermal stability of HNR vulcanizates was better than that of NR vulcanizate. Thus, this chemical modification seems to give a promising NR derivative whose properties can be equivalent or even better than the mother polymer. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on damping properties of HVBR/EVM blends prepared by in situ polymerization

In comparison with normal damping rubbers such as natural rubber (NR), styrene butadiene rubber (SBR), isobutylene isoprene rubber (IIR) etc., Mo-based high vinyl polybutadiene rubber (HVBR) with high loss factor, excellent aging resistance and glass transition temperature closer to room temperature, is a promising damping material. The effective damping temperature range of HVBR could be further broadened by blending with ethylene-vinyl acetate (EVM) and the effects of blending methods (in situ polymerization blending or mechanical blending) and blending ratios on the damping properties and physical properties of HVBR/EVM blended rubber were studied. HVBR/EVM in situ polymerization blends was prepared by butadiene coordination polymerization by Mo-base catalyst in a toluene solution of EVM. The results of dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) of the blended vulcanizates via in situ polymerization blending revealed that the compatibility between HVBR and EVM was improved compared with that of the blended vulcanizates via the traditional mechanical blending method. The two phases of HVBR/EVM in situ polymerization blends had good dispersion and uniformity, the damping temperature range was significantly expanded, and the peak and valley of the damping temperature range were greatly improved. A blending ratio of HVBR/EVM900 = 100/40 showed the best damping properties and the effective damping temperature range (tanδ>0.3) was extended from −6.6 °C to 39.4 °C.     

Reinforcement of compatibilized NR/NBR blends by fly ash particles and precipitated silica

Effects of precipitated silica (PSi) and silica from fly ash (FA) particles (FASi) on the cure and mechanical properties before and after thermal and oil aging of natural rubber (NR) and acrylonitrile–butadiene rubber (NBR) blends with and without chloroprene rubber (CR) or epoxidized NR (ENR) as a compatibilizer have been reported in this paper. The experimental results suggested that the scorch and cure times decreased with the addition of silica and the compound viscosity increased on increasing the silica content. The mechanical properties for PSi filled NR/NBR vulcanizates were greater than those for FASi filled NR/NBR vulcanizates in all cases. The PSi could be used for reinforcing the NR/NBR vulcanizates while the silica from FA was regarded as a semi‐reinforcing and/or extending filler. The incorporation of CR or ENR enhanced the mechanical properties of the NR/NBR vulcanizates, the ENR being more effective and compatible with the blend. The mechanical properties of the NR/NBR vulcanizates were improved by post‐curing effect from thermal aging but deteriorated by the oil aging. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of the mechanical properties at similar hardness level of natural rubber filled with various reinforcing-fillers

Commercially, the alteration of a rubber formulation is usually made in such a way as to keep the hardness of the rubber product constant. This is because a specific hardness of the rubber product sets the limit to its practical applications. Therefore, in this paper, natural rubber (NR) vulcanizates containing various fillers were prepared to have the same hardness level, and their mechanical properties were compared and related to the degree of filler dispersion. The results show that higher amounts of carbon black (CB) and silica are needed for CB- and silica-filled natural rubber vulcanizates to achieve the same hardness value as a NR vulcanizate containing 6 phr of montmorillonite clay. At equal loading of fillers, clay-filled vulcanizate exhibits higher modulus, hardness, tensile strength and compression set, but lower heat build-up resistance and crack growth resistance than those of the vulcanizates containing conventional fillers. For the vulcanizate having the same hardness value, CB-filled vulcanizate gives the better overall mechanical properties followed by the clay-filled and silica-filled vulcanizates, respectively. The explanation is given as the better dispersion of carbon black, as can be seen in the SEM micrograph.     

Foaming of trans‐polyisoprene using N2 as the blowing agent

Foaming of trans‐1,4‐polyisoprene (TPI) polymer was carried out through a batch process using nitrogen (N₂) as the blowing agent. TPI vulcanizates having varying crosslink densities were prepared by varying crosslinking agent content and curing time. The vulcanizates were then saturated with N₂ inside a pressure vessel at a pressure of 14 MPa and varying temperatures for 5 hours before effecting the foaming by rapidly quenching the pressure. The effects of varying the crosslinking agent content, silica filler content, and precuring time of the vulcanizates and the effects of varying the gas saturation temperature of foaming on the cell characteristics and physical properties of the foam prepared were investigated. The cells of the TPI foams had a spherical, closed structure. The density, expansion ratio, cell size, cell density, and tensile properties of the foams varied with varying crosslink density of the TPI vulcanizates as well as the saturation temperature of foaming. The important effects of crosslink density and saturation temperature on the N₂ solubility in the TPI matrix and thus on the foam expansion were discussed. The silica filler was found to be acting as a cell nucleating agent and reinforcing filler for the TPI foams.     

Preparation and properties of graded styrene‐butadiene rubber vulcanizates

Styrene‐butadiene rubber (SBR) vulcanizates with graded network‐chain densities in the thickness direction were prepared by layering and heat pressing the compounding sheets. The effect of the gradient of network‐chain density on the mechanical properties of the graded rubber vulcanizates was investigated in comparison with those of SBR vulcanizates that were prepared from the homogeneous compounding sheets. The matrix with a high network‐chain density exclusively affected the mechanical properties of the graded rubber vulcanizates when the gradient was given in the thickness direction. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 358–364, 2002; DOI 10.1002/polb.10096     

Thermal properties of flame retardant viscose fibers

This paper discusses the problem of the thermal properties of flame retarding additives based on phosphazene derivatives and of the commercial agents TomflamB, FlammexT23P and StockhausenW-20949, as well as of flame resistant viscose fibers containing the above agents. Results of this investigation showed the action of FlammexT23P, StockhausenW-20949 and phosphazene derivatives at lower temperature. TomflamB acted within a much wider range of temperatures. The flame retardant additives applied to viscose fibers change the thermal properties of the fiber material.     

溶胶-凝胶法原位生成SiO2改性硅基耐烧蚀材料

建立了在硅基耐烧蚀材料中用溶胶-凝胶法原位生成SiO2的方法.首先将硅橡胶、气相白炭黑、纤维等原料混炼硫化制备出硫化胶.然后将硫化胶依次浸入四氢呋喃、原硅酸乙酯和正丁基胺水溶液中进行预溶胀处理、物理扩散和化学反应,得到原位生成SiO2.SEM照片显示,在硅基耐烧蚀材料中原位生成的SiO2颗粒呈球形,粒径在40~60 nm,但分布不均匀,在硫化胶表层存在富集现象.实验结果表明,原位生成SiO2平均含量增加,硅基耐烧蚀材料的抗拉强度增加,线烧蚀率下降;含13.7%原位生成SiO2硅基耐烧蚀材料抗拉强度为5.82 MPa,线烧蚀率为0.071 mm/s.