Density Of Vulcanizates Research Articles

Thermal Conductivity of Silicone Rubber Filled with Al<sub>2</sub>O<sub>3</sub>

Crosslinker (polyvinylsilicone oil, C gum) and curing agent (2, 5-bis (tert-butyl peroxy)-2, 5-dimethyl hexane, DBPMH) were used to change the crosslink density of the thermal conductivity of silicone rubber filled with Al2O3. The results show that the thermal conductivity of silicone rubber changed with its degree of crosslinking. When the Al2O3 loading was 5 vol. % and a completely continuous conducting network had not formed, the thermal conductivity of the vulcanizates decreased with increasing crosslink density. The thermal conductivity of the vulcanizate with a suitable amount of C gum increased to 53%, and the tensile strength increased by 0.8 MPa compared to the vulcanizate without C gum. When the Al2O3 loading was 30 vol. % and a completely continuous conducting network had formed, the crosslink density of vulcanizates changed as the amount of DBPMH changed. The thermal conductivity of vulcanizates first decreased and then increased with increasing crosslink density. There was a valley value in the thermal conductivity–crosslink density curve.

Study on the preparation of graphene oxide/silica/natural rubber latex composites by different processes

In this study, the graphene oxide/silica/natural latex composites were prepared by four different processes, including spray sputtering drying method, dry-ice–expansion predispersion method, mechanical stirring method, and traditional drying method. Compared to the other three methods, the spray sputtering method had higher physical mechanical properties and better silica dispersion in the rubber matrix. Meanwhile, the cross-linking density of vulcanizates prepared by the spray sputtering drying method is the largest. Compared with the compound prepared by mechanical stirring, the tensile strength, tear strength, and wear resistance property of the compound prepared by spray sputtering drying method increased by 13.6%, 31.5%, and 16.7%, respectively. The tensile strength, tear strength, and wear resistance property of the compound prepared by spray sputtering drying method increased by 27.2%, 43.6%, and 24.6%, respectively, than those prepared by dry mixing method.

Innovative Application of Biopolymer Keratin as a Filler of Synthetic Acrylonitrile‐Butadiene Rubber NBR

The current investigations show the influence of keratin, recovered from the tanning industry, on the thermal and mechanical properties of vulcanizates with synthetic rubber acrylonitrile‐butadiene rubber NBR. The addition of waste protein to NBR vulcanizates influences the improvement of resistance at high temperatures and mechanical properties like tensile strength and hardness. The introduction of keratin to the mixes of rubber previously blended with zinc oxide (ZnO) before vulcanization process leads to an increase in the cross‐linking density of vulcanizates. The polymer materials received including addition of proteins will undergo biodecomposition in natural conditions. After soil test, vulcanizates with keratin especially keratin with ZnO showed much more changes on the surface area than vulcanizates without protein. In that aerobic environment, microorganisms, bacteria, and fungus digested better polymer materials containing natural additives.

The Influence of Nanostructured Metal Oxides and Unsaturated Acids on Peroxide Cross-Linking of Ethylene-Octene Rubber

This paper deals with blends of ethylene-octene rubber (POE) with nanostructured metal oxides: magnesium oxide (MgO), calcium oxide (CaO), zinc oxide (ZnO) and unsaturated acids: itaconic acid (IA), sorbic acid (SA) and crotonic acid (CA), as co-agents. Dicumyl peroxide (DCP) was used as a vulcanizing agent. Elastomer composites were prepared in Brabender measuring mixer N50. Rheometric properties of rubber mixes and crosslink density of vulcanizates were measured. Mechanical properties of the samples were also investigated. Dispersion degree of coagents in elastomer matrix was studied by SEM images. Cross-link density analysis revealed that POE vulcanizates contained both ionic bonds and covalent bonds. The results showed that the nanostructured metal oxides and unsaturated acids used as co-agents can greatly improve the modulus at 100% of elongation and tensile strength of the vulcanizates.

Crystallization of vulcanizates. I. Low‐temperature crystallization as a function of extent of cure for polyisoprene vulcanized with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur

AbstractThe crystallization of polyisoprene, vulcanized to various degrees of cure with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur formulations, was studied in a density column at −25°C. The densities of vulcanizates before crystallization decrease progressively with cure time, which is ascribed to an increase in free volume occasioned by the formation of accelerator‐terminated pendent groups on the polymer chain. The induction period before the onset of crystallization increases and both the rate of and the degree of crystallization decrease with extent of cure. This is attributed primarily to the presence of residual pendent groups on the polymer chain and secondly to crosslink formation. The changes are more marked with MBTS formulations where pendent groups are more bulky. MBTS compounds fail to crystallize once vulcanized to the point where a gel has formed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2565–2572, 2001

Study on the compatibility of BR/CR/SBS blends by using small amounts of SBS

The structures and properties of BR/CR/SBS blends were studied by using optical, electron microscopy, FTIR methods, etc. Results showed that the addition of a small amount of SBS to the thermodynamically immiscible blends BR/CR could significantly promote fine and homogeneous dispersion of the system, increase crosslink density of vulcanizates and tensile strength, and decrease loss of tan δ of the blends. IR spectra also demonstrated the stronger interaction between SBS and BR, CR. The theoretical prediction of compatibilizing activity of SBS in the BR/CR blends is in excellent agreement with experimental results.

Effects of some phenylethynylsilicon compounds on heat‐curable silicone rubber. I. 1,3‐bis(methylphenylethynylvinyl)disiloxane

AbstractWe have investigated the effects of 1,3‐bis (methylphenylethynylvinyl) disiloxane (BMPVDS) as crosslinker on heat‐curable silicone rubber and measured sol fractions and crosslink density of vulcanizates by benzene‐extract and toluene‐swelling methods, respectively. The experimental results show that, adding suitable amounts of BMPVDS, the vulcanizates exhibited rather fine mechanical properties. The tear strength of some vulcanizates could reach as high as 60.31 kN/m, the tensile strength 13.46 MPa, and the modulus at 100% extension 2.45 MPa, and the permanent deformation is rather low. BMPVDS is also a good curing retarder of hydrosilation curing silicone rubber. When adding 0.08 part of BMPVDS or more, the stocks can store at 20 ± 1°C more than 50 days without curing.

Molecular Structure and Macroscopic Properties of Synthetic Cis-Poly(Isoprene)

Abstract By changing the sol-gel ratio and the structure of the gel fraction it is possible to obtain various grades of synthetic cis-poly(isoprene) which show promise for different applications in the tire and mechanical rubber goods industries. The processability of commercial SKI-3 rubber (at a given average molecular weight of sol) depends mainly on the structure of the gel fraction. Thus, for example, inferior processing properties of rubber compounds is associated primarily with the presence of tight gel. The content and structure of the gel fraction also significantly affect plasto-elastic properties of raw rubbers, e.g. a low plasticity of raw rubbers owes to the increased content of gel fraction. The reduced green strength of compounds based on SKI—3 rubber is accounted for by its chemical structure. Conventional methods used to change the properties of rubbers (including the variation in molecular weight, molecular weight distribution, branching degree, and variation in the content and structure of gel fraction) cannot be considered to be adequate to tackle the problem of the green strength of SKI—3 black stocks. The way to solve the problem appears to be the introduction of functional groups into the polymer chain at the stage of synthesis or processing. These functional groups should be active as to the formation of labile rubber—carbon black—rubber and/or rubber—rubber bonds. High purity of microstructure is necessary but not sufficient for obtaining the required level of green strength of compounded SKI—3. The gel fractions of SKI—3 rubber yield vulcanizates with a more dense network than the corresponding sol vulcanizates. The temperature dependence of the tensile strength is controlled by the network density of vulcanizates from high cis-1,4 poly(isoprene).

Rubber—Black Interaction Influence on Cure Level of Vulcanizates

Abstract The crosslink density of vulcanizates has been quantitatively investigated using swelling measurements (Vr) of compounds of cis-1,4-polybutadiene reinforced with N242, N326, or N990 (Vulcan 6H, Regal 300, Sterling MT). Crosslink density in both filled and unfilled stocks is shown to be related to the molar concentration of the curatives in the unbound rubber phase of the vulcanizates and not merely to total concentration. The effects of different carbon black loadings and of cure time are demonstrated to be fully describable by the extent of carbon black—rubber interaction, measured by bound rubber; that occurs during mixing and during the induction period of the cure step. Greater rubber-black interaction, whether achieved by higher black level or from higher reinforcing blacks, always yielded vulcanizates of increased crosslink density compared to an identically vulcanized gum control. Calculating curative concentration on the basis of unbound rubber—rather than total rubber—illustrated the expected dependence of crosslink density upon curative concentration and graphically explains the presence of so-called “excess” crosslinks. Implied, also, is one cause for the “scorchy” character of highly reinforcing blacks and the higher modulus obtained with these blacks.

Reversion during TMTD Vulcanization

Abstract 1) Reduction of crosslink density of vulcanizates (reversion of vulcanization) is observed during vulcanization of a mixture prepared in air of NR and SKI with TMTD without metal oxides and with magnesium and calcium oxides. In these cases the dimethyldithiocarbamic acid formed during vulcanization decomposes into carbon disulfide and dimethylamine. 2) During mixing and curing of these mixtures in an argon atmosphere reversion is absent although evolution of carbon disulfide and dimethylamine is observed. 3) During vulcanization of the mixtures containing zinc oxide no reversion occurs as a result of preparation of the mixtures either in air or in argon. Dimethyldithiocarbamic acid in this case is bound in the form of the stable zinc dimethyldithiocarbamate. 4) Reversion of rubber by TMTD is explained by oxidative destructive processes which are intensified by the products of decomposition of dimethyldithiocarbamic acid, i.e., by carbon disulfide and dimethylamine, and are suppressed by reaction of it to form zinc dimethyldithiocarbamate which serves as an inhibitor of the oxidative destruction of the vulcanizate.