Influence of Modification on the Elastic-Relaxation Properties of Rubbers Based on Binary Blends of Diene Rubbers

The elastic-relaxation properties of rubbers based on binary blends of diene rubbers were studied as influenced by the modifier, trichloroacetic acid.     

高热稳定性硅橡胶的研究

阐述了在硅橡胶主链中引入硅氮结构,在硅橡胶中添加硅氮化合物或采用硅氮交联剂对改进硅橡胶热稳定性的影响,提出了利用Ｓｉ－Ｎ键的反应去消除引起硅橡胶主链降解的硅羟基和水平达到提高其热稳定性的作用机理。采用阴离子活性聚合的方法合成了具有低玻璃化温度的耐高温的聚硅氧烷弹性体。     

Polymer flammability. II

The responses of a polymer flame to changes of specimen diameter, ignition position, and stability of the burning surface were determined. These extrinsic flame parameters restricted the transport of oxygen from the environment to the burning surface. With increasing restriction the oxygen demand from the environment for self-sustained combustion increased from a minimum oxygen demand at maximum access of environmental oxygen to the burning surface. This increase in oxygen demand was measured and correlated with surface oxygen concentrations estimated from the diffusion data of Part I. The minimum oxygen demand was demonstrated as characteristic for a given polymer and intrinsic in its chemical structure. This minimum oxygen demand, termed intrinsic combustibility, has been correlated with a polymer's thermooxidative stability, measured by thermogravimetric analysis at specific conditions. An intrinsic combustibility scale for polymers is given. In contrast, polymer flammability, as commonly measured in air, is interpreted as a variable property that depends on the extent of the interaction between extrinsic parameters, which are set by the testing configuration, with intrinsic combustibility.     

Polymer flammability. I

The transport of oxygen by diffusion from the environment into a gas stream was investigated as a model for the analogous process in a diffusion flame. The amount transported at steady-state conditions depended on the flow rate, diameter, and spatial orientation of the gas stream. A change of the same extrinsic parameters in a diffusion flame caused changes of burner surface temperature, maximum flame temperature, and flame height. These responses were correlated and yielded an overall activation energy of the rate-controlling reaction step in the combustion process equal to 49 kcal/mole. This value was the same for several types of diffusion flames examined and appeared to be associated with the CO/CO₂ conversion process at the high-temperature flame boundary. Flame quenching was demonstrated to occur at a minimum fuel flow rate and minimum environmental oxygen concentration which were characteristic for a given fuel. Quenching conditions were related to the diffusion rate of oxygen into the product effluent stream. Quenching of a polymer flame by depletion of environmental oxygen was governed by the same processes. The effect of extrinsic parameters on polymer flames is discussed in Part II.     

Thermal analysis of flammability

The present article describes the synthesis, structural features and thermal studies of the complexes of the type [M(SB)₂(H₂O)₂]·nH₂O [where HSB=pyridine-m-carboxaldene-o-aminobenzoic acid and M=Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)]. The complexes have been characterized on the basis of elemental analyses, magnetic susceptibility measurements, (FTIR and electronic) spectra and thermal studies. The nature of the bonding has been discussed on the basis of infrared spectral data. Magnetic susceptibility measurements and electronic spectral data suggest a six-coordinated structure of these complexes. The complexes of Mn(II), Co(II), Ni(II), Cu(II) are paramagnetic, while Zn(II) and Cd(II) are diamagnetic in nature. The thermal decomposition of the complexes have been studied and indicates that not only the crystallization and coordinated water are lost but also that the decomposition of the ligand from the complexes is necessary to interpret the successive mass losses. The kinetic parameters such as order of reaction (n) and the energy of activation (E _a) have been reported using Freeman–Carroll method. The entropy (S*), the pre-exponential factor (A), the enthalpy (H*) and the Gibbs free energy (G*) have been calculated.     

Influence of Filler on Elastic-Relaxation Properties of Vulcanized Rubbers Based on Binary Blends of Diene Rubbers

The strength, elastic-relaxation properties of vulcanized rubbers based on binary blends of diene rubbers were studied as influenced by a filler, carbon black no. 330.     

Effect of Polycaprolactam Fiber on Coagulation of Rubbers and on Properties of Rubbers,Rubber Stocks,and Vulcanizates

The effect of polycaprolactam fiber on the coagulation of butaidene-styrene rubber from the latex was studied.     

Evaluate the flammability of a PU foam with double-scale analysis

Two-scale tests, microscale and bench scale, are conducted to analyze the flammability of a flexible polyurethane foam. Microscale tests include simultaneous thermal analysis coupled to Fourier transform infrared spectroscopy, and microscale combustion calorimeter (MCC). Evolved gas components, heat release rate per unit mass, total heat release, derived heat release capacity, and minimum ignition temperature are obtained. Bench scale tests are performed on cone calorimeter. Peak heat release rate per unit area, effective heat of combustion, minimum incident heat flux for ignition, and total heat release per unit area of different incident heat fluxes are obtained. FO-category of the PU foam is estimated by multiple discriminant function analysis based on the results of cone calorimeter test. The relationship between the two-scale tests is analyzed. The minimum ignition temperatures derived from multi heating rate MCC tests are used to predict the time to ignition and compared with the results from cone calorimeter tests. This PU foam is evaluated as a high fire hazard polymer having low heat release capacity, low ignition temperature, and short ignition time.

     

Polymers with improved flammability characteristics. I. Phenolphthalein-related homopolymers

Improved fire resistance occurs for phenolphthalein-related polycarbonates and polyesters compared to bisphenol-A polymers and emphasizes the importance of polymer composition and polymer structure in affecting the flammability of a polymer. Phenolphthalein-related polymers are able to produce a higher degree of crosslinking during pyrolysis which subsequently leads to higher char yields. The correlations between oxygen index and char yield for various polymers are obtained and discussed. Polycarbonates and polyamides usually show higher oxygen indices than the corresponding polyesters of related structures. This indicates that the nature of the pyrolysis products has a measurable effect on the flammability of a specific polymer. Among many factors, polycarbonates should release more CO₂ from the breakdown of the carbonate group, and polyamides should produce relatively nonflammable nitrogen-containing products during pyrolysis, thus accounting in part for these results.     

橡胶的老化机理及老化行为的研究进展

橡胶制品在使用过程中会受到热、氧、热氧、光、辐照及机械应力等因素影响,会产生降解、交联等老化行为.不同种类橡胶因其使用环境和要求不同,其老化机理也各不相同.本文介绍了橡胶老化的化学机理、研究方法及预测方法和模型,综述了近年来不同品种的橡胶及橡胶/橡胶并用体系的老化行为研究进展.通过对橡胶老化行为和机理的综述,有助于系统...     

Comparison of Some Soft Unplasticized Cast Polyurethane Rubbers

Different types of unplasticized cast polyurethanes with hardness around 60 Shore A have been compared. The tensile properties, tear strength, resistance to hydrolysis, and swelling in solvents and water were examined. The influence of composition on the properties of cast polyurethanes prepared from a polyadipate polyol and diisocyanates, including the effect of a range of fillers, was investigated in detail. Fumed silica, fumed alumina, and carbon black significantly increased the hardness and tensile strength of the rubber, whereas kaolin and talc gave small increases. Ground silica, calcite, and rutile had no effect. No significant increases in tensile strength were obtained with silane and titanate coupling agents with a fumed silica filler. The rate of hydrolysis or extent of swelling in xylene was unchanged by fillers.     

Reactivity and flammability of conjugated acetylenes

The thermal reactivities of model phenyleneacetylenes and diacetylenes and of poly(butadiynylene-1,3-phenylene) have been examined by differential scanning calorimetry and compared with the oxygen indices of the materials. No direct relationship was found between the heat of reaction and the oxygen index in these compounds. However, the heat of reaction, in general, does decrease with increasing molecular weight and is lower for rigid linear molecules than for related angular structures. These observations appear to be due to a lack of solid-state reactivity in the crystalline phase and retardation in the melt due to viscosity effects related to molecular size and rigidity. The synthesis of model compounds is described.     

Thermal stability and flammability of butadiene- acrylonitrile rubber cross-linked with iodoform

Summary The paper discusses the results of thermal analysis and flammability of butadiene-acrylonitrile rubber, Perbunan NT 1845 of Bayer, cross-linked with iodoform. The properties of the iodoform vulcanizate have been compared with those of peroxide vulcanizate. The thermal analysis has been performed in air with use of a derivatograph under air and nitrogen atmosphere as well as dynamic scanning calorimetry (DSC). The flammability of vulcanizates has been determined by the method of oxygen index and in air. The toxicity of the thermal decomposition and combustion products of the vulcanizates under investigation has been also determined. Based on complementary examinations, DTA and DSC curves have been interpreted from the point of view of thermal transitions of the conventionally and non-conventionally cross-linked nitrile rubbers. The glass transition temperature of the cross-linked polymer both in cooling and heating has been determined.     

Thermal stability and flammability of polyurethane foams chemically reinforced with POSS

Manganese ferrite nanopowder was prepared by a new solvothermal method, using 1,2 propanediol as solvent and KOH as precipitant. The as-synthesized powder, by solvothermal treatment in autoclave at 195 °C, for 12 h, consisted of fine manganese ferrite nanoparticles. The further thermal treatment of the initial manganese ferrite powder to higher temperature resulted in manganese ferrite decomposition due to Mn(II) oxidation to Mn(III), as observed by X-ray diffraction. FT-IR spectroscopy has evidenced that the oxidation takes place even at 400 °C. The oxidation of Mn(II) to Mn(III) was studied by TG/DSC simultaneous thermal analysis. It was shown that Mn(II) oxidation takes place in a very small extent up to 400 °C. The main oxidation step occurs around 600 °C, when a clear mass gain is registered on TG curve, associated with a sharp exothermic effect on DSC curve. The exothermic effect is smaller in case of the powder annealed at 400 °C, confirming the superficial oxidation of Mn(II) up to 400 °C. In order to avoid Mn(II) oxidation, the powder obtained at 400 °C was further annealed at 800 °C in argon atmosphere, without degassing, when manganese ferrite MnFe₂O₄ was obtained as major crystalline phase (69 %). All manganese ferrite powders showed a superparamagnetic behavior, with maximum magnetization of 51 emu g^?1 in case of the as-synthesized powder, characteristic of magnetic ferrite nanopowders.     

Preparation of Compounds of Epoxy Resins with Low-Molecular-Weight Carboxyl-containing Rubbers by Activating Mixing

A process was developed for preparing adhesives from a low-molecular-weight carboxyl-containing rubber and an epoxy resin with different oligomer ratios. The process involves the chemical reaction of the components under conditions of activating mixing.     

Polymers with improved flammability characteristics. II. Phenolphthalein related copolycarbonates

Analysis of phenolphthalein and bisphenol-A copolycarbonates reveals a linear correlation between oxygen index (OI) and char yield (Y): OI = 0.34Y + 19.6, which can be compared with the empirical equation QI = 0.4Y + 17.5 proposed by D. W. Van Krevelen for other polymers. Analysis also suggests that no chemical interction occurs between the two comonomers during pyrolysis, which leads neither to enhanced char yield nor to enhanced oxygen index. Each copolymer component contributes to the char yield and oxygen index on an additive basis. Study of 4,5,6,7-tetrabromophenolphthalein and phenolphthalein copolycarbonates shows that some enhancement of char yield does occur and that the lower the char yield, the higher the oxygen index, which is an indication of the predominance of a vapor-phase bromine effect over that related to char. Study of 4,5,6,7-tetrabromophenolphthalein and bis-phenol-A copolycarbonates is interpreted on the basis of two factors—the char effect that prevails over the vapor phase radical scavenging effect at lower bromine content and the reverse order at higher bromine content.     

A Comparative analysis of polymerization filled polyethylene composites with reduced flammability

Fire-resistant polyethylene-based composites and self-extinguishing composites with high stress-strain characteristics have been synthesized with vanadium-based Ziegler-Natta catalysts in the presence of fillers, such as aluminum hydroxide and complex flame retardants based on aluminum hydroxide and decabromodiphenyl oxide in combination with Sb₂O₃. The correlation between oxygen index and filler content in the composites has been established. Empirical relationships relating oxygen index to the formulation and content of flame-retardant agents in the composites are proposed; these relationships allow one to predict flammability of the filled PE without any fire tests.     

Activating Mixing in Modification of Rubbers in Solution

The applicability of the previously developed principles of activating mixing to modification of rubbers in solutions was tested, and a process was developed for mechanochemical modification of cis-1,4-polyisoprene in rotary pulsation apparatus.     

炭黑／SBS／橡胶复合材料的电学性能

用炭黑填充ＳＢＳ／橡胶制备导电复合材料。研究了复合材料的导电性、电阻率随温度变化的特性。讨论了炭黑填充率、炭黑结构和性质以及ＳＢＳ对复合材料导电性和电阻率－温度特性的影响。实验结果指出，使用中等结构炭黑（Ｎ５５０）填充ＳＢＳ／橡胶共混基体可获得一定强度的ＰＴＣ复合材料；适量填充ＳＢＳ可改善ＳＢＳ／橡胶复合材料的高温ρ￣Ｔ特性，硫化ＳＢＳ／ＳＢＲ可减轻其滞后性。