Elastic behavior of natural rubber filled vulcanizates

The reinforcement effect of carbon black and, the effect of accelerator-to-sulfur ratio variation on the elastic behavior of natural rubber vulcanizates have been studied. The Mooney–Rivlin relation was used to describe the behavior of the rubber matrix, and values of constants c₁ and c₂ have been evaluated with the use of the strain-amplification factor. The stress softening of the vulcanizates tested has also been examined.     

氧化亚铁硫杆菌脱硫天然橡胶粉及其填充胶的性能

从铁矿土壤中分离出1株氧化亚铁硫杆菌,比较了其在不同Fe2+质量浓度的改进9 K培养基中的生长情况,确定最佳的天然橡胶胶粉加入时间为培养开始后的第30 h。利用氧化亚铁硫杆菌在较低Fe2+质量浓度的改进9 K培养基中进行脱硫实验,脱硫橡胶表面的傅里叶变换红外光谱、X射线光电子能谱分析和培养液中SO42-的浓度变化都表明氧化亚铁硫杆菌是通过氧化硫黄的代谢途径来断裂橡胶中的硫黄交联键。用该脱硫胶粉填充天然橡胶硫化胶的力学性能有一定程度的提高;通过扫描电子显微镜可以看出脱硫胶粉与天然橡胶基质的界面结合较好,应力集中点较少,脆断面的断裂线均匀。     

A study of sulfur bridges in filled natural rubber vulcanizates by pyrolysis gas chromatography with flame-photometric detection

Natural rubber vulcanizates of two formulations, with sulfur/N-cyclohexyl-2-benzothiazolesulfenamide (CBS) and tetramethylthiuram disulfide (TMTD), respectively, were analyzed by pyrolysis gas chromatography. A sulfur-selective flame-photometric detector was utilized. The main pyrolysis products were identified as CS₂ and some thiophenes. The yields of the pyrolysis products from the two types of rubber were very different. The yields also varied with the curing time of the rubbers.     

Determination of carbon black fillers in vulcanizates of natural rubber by metathesis degradation

A method for the determination of carbon black fillers in peroxide vulcanizates or sulfur vulcanizates of natural rubber (NR, cis-1,4-polyisoprene) by metathesis degradation with 1-octene was developed using the catalyst WCl₆? (C₂H₅)₃Al₂Cl₃. The carbon black was separated from the reaction mixture by centrifuging and determined by weighing. In this connection, investigations were also performed with the catalyst WCl₆? C₂H₅Al₂Cl₃ which was less suitable for filler determination. The rate of degradation of crosslinked NR with (E)-4-octene was measured. Metathesis reactions of 2-methyl-2-pentene (low-molecular-weight model compound of NR) with 7-tetradecene showed the importance of double bond shift for the degradation of NR.     

Physicomechanical properties of filled natural rubber vulcanizates modified with phosphorylated cashew nut shell liquid

Effect of fillers like carbon black, silica, and china clay on the cure characteristics and physicomechanical properties of natural rubber (NR) modified with phosphorylated cashew nut shell liquid (PCNSL) in various proportions has been studied. Prominent cure retardation has been observed with progressive increase in concentration of PCNSL from 0 to 20 phr. The softening effect of PCNSL on the vulcanizate has been displayed by the linear decrease in hardness and tensile modulus and the increase in elongation at break with the increase in concentration of PCNSL. The results on the tensile and tear strengths of the vulcanizates showed that the reinforcing effect of the fillers were maximized at concentrations of PCNSL ranging from 5 to 10 phr. Also, the PCNSL-modified NR vulcanizates showed improved resistance to thermo-oxidative ageing and decomposition, especially at the higher concentration of 20 phr. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1303–1311, 1998     

酵母菌生物脱硫胎面胶粉及其填充天然橡胶的力学性能

用酵母菌对胎面胶粉(GTR)进行了生物脱硫实验,考察了酵母菌与GTR共培养脱硫过程中酵母菌的生长情况,对比了GTR和脱硫GTR(DGTR)填充天然橡胶(NR)硫化胶的交联密度、表面元素含量和力学性能.结果表明,在共培养脱硫过程中酵母菌依然可以保持较高的生物量,脱硫6 d后可获得生物脱硫的GTR.随着胶粉用量的增加,填充NR硫化胶的交联密度和力学性能逐渐降低.相比较GTR/NR硫化胶,DGTR/NR硫化胶的表面硫元素含量和交联密度更低,力学性能明显提高.     

Crack growth and abrasion resistance of carbon black‐filled purified natural rubber vulcanizates

The influence of parameters contributing to rubber stiffness, including, crosslink density, hardness, and modulus, on the crack growth and abrasion resistance of carbon black‐filled purified natural rubber (PNR) vulcanizates as well as a whole natural rubber (WNR) vulcanizate counterpart or a control were elucidated. In addition, the tensile properties of PNR and WNR were also determined. PNR containing the same curative level as that of the control had lower stiffness and exhibited superior crack growth resistance. The results revealed that the improved crack growth resistance of PNR, compared to the control, was due to its lower crosslink density, hardness, and modulus. In addition, the tensile strength and abrasion resistance of PNR vulcanizates were not as sensitive as the crack growth resistance to the changes of their stiffness. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1793–1796, 2003     

Mechanistic study of the antioxidant activity of decarboxylated cashew-nut-shell-liquid in natural rubber vulcanizates

The antioxidant activity of decarboxylated cashew-nut-shell-liquid (CNSL), which consists of a monophenol, anacardol and a diphenol, cardol, each with a bulky unsaturated alkyl group at the meta position, in sulphur-cured natural rubber vulcanizates has been found to be mainly due to the formation of phenolic sulphides in situ during vulcanization. The sulphides are formed through a substitution reaction probably at the para position to the phenolic group. It has also been observed that cardol, the diphenolic component, contributes more towards the antioxidant activity than the monophenol, anacardol. This has been explained as being due to the high probability of formation of the sulphides with cardol.     

Stress softening in natural rubber vulcanizates. Part IV. Unfilled vulcanizates

Stress softening (Mullins effect) is observed in gum natural rubber vulcanizates. The magnitude of this softening is similar to that in carbon black-filled vulcanizates. The amount of stress softening is slightly greater in vulcanizates cured to produce predominantly polysulfide crosslinks than in those containing monosulfide or carbon–carbon crosslinks. The total recovery of stress softening in the vulcanizates containing monosulfide or carbon–carbon crosslinks suggests that the phenomenon is attributable to a quasi-irreversible rearrangement of molecular networks due to localized nonaffine deformation resulting from short chains reaching the limit of their extensibility. This non-affine deformation results in a displacement of the network junctions from their initial random state.     

Comparative study on natural antioxidant as an aging retardant for natural rubber vulcanizates

The research aim is mainly to investigate the effectiveness of natural antioxidant (NA) obtained from oil palm leaves (Elaeis guineensis) as an aging retardant in natural rubber (NR) vulcanizates. Comparison of NA with other commercial antioxidants, trimethyl quinoline (TMQ) and butylated hydroxy toluene (BHT), is investigated. The effect of natural and commercial antioxidants on NR vulcanizates was explored before and after aging. Aging test was carried out at 70°C for three different periods, 4, 7, and 14 days to determine aging property by performing the tensile and tear tests. NA shows lower tensile properties, crosslink density, tack strength but high tear strength compared to the commercial antioxidants, BHT and TMQ. However, upon aging NR vulcanizates with NA retains its properties equivalent to that of commercial antioxidants, BHT and TMQ. Thus, NA can be used as an aging retardant for short‐term protection in application requiring moderate tensile properties and can be used as alternative source for commercial antioxidant. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Studies on double networks in natural rubber vulcanizates

The concept of double networks is a rather new idea, by which one imparts chain orientation in elastomers. Double networks were made in natural rubber vulcanizates cured with a single and a new binary accelerator system. Double networks with different extensions were prepared and their effects on tensile properties were analyzed. The influence of extent of initial cure on double‐network formation was examined. Thermal stability of the double network formed was analyzed by ageing of the double networks and was found to improve with residual extension. Crosslink density of the networks formed was determined by swelling methods and stress–strain analysis. It was found that crosslink density increased with double‐network formation and residual extension. The stress–strain behavior and moduli were analyzed to study the effect of these properties on double‐network formation. Double networks were hardly affected by the binary accelerator system. Based on the studies it was found that residual extension was the major factor determining the final properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1068–1076, 2004     

Stress softening in natural rubber vulcanizates. Part III. Carbon black-filled vulcanizates

Stress softening (Mullins effect) occurs in rubber vulcanizates during the first and subsequent deformations. This paper shows the similarity of the degree of stress softening in both unfilled and carbon black-filled vulcanizates of natural rubber when stressed almost to break. This confirms the earlier investigations which were confined to moderate stresses. A simple interpretation of the tensile stress–strain results for filled rubber is that the strain in the rubber is increased by the presence of the filler, so that the ratio of the average strain in the rubber to the measured overall strain is given by a strain amplification factor. The usefulness of this concept is confirmed by showing the similarity of the stress-softened curves after normalizing the strains, provided the vulcanizates of both gum and filled vulcanizates were subjected to the same initial stress.     

Properties of natural rubber vulcanizates containing mechanochemically devulcanized ground tire rubber

The devulcanization of ground tire rubber (GTR) was carried out with a self-designed pan-mill type mechanochemical reactor. Gel fraction and crosslink density measurements confirmed the occurrence of stress induced mechanochemical devulcanization of GTR. The partially devulcanized GTR (dGTR) was blended with virgin natural rubber (NR) at different ratios. The curing characteristics and mechanical properties of these composites were investigated and compared with those composites of raw ground tire rubber (rGTR) and NR. The results showed that the tensile properties of the dGTR/NR vulcanizates were much better than those of the rGTR/NR vulcanizates, which are comparable to or even better than the virgin vulcanizate, indicating the significant benefit of mechanochemical devulcanization. At the GTR content of 10%, the tensile strength of the dGTR/NR blends increased to 23.2 MPa from 13.7 MPa of the rGTR/NR blends, enhanced by 69% through partial devulcanization of GTR, and the elongation at break increased by 47%.     

Dynamic properties of PBNA–natural rubber vulcanizates

Some crystalline organic compounds containing a β-naphthyl group stiffen rubbers considerably. This paper discusses the dynamic behavior of these systems when subjected to oscillatory strain of increasing amplitude. Modulus–strain amplitude plots similar to that in carbon black–natural rubber systems are obtained. The implication of these results to reinforcement theory is discussed.     

Effect of mica addition on the properties of natural rubber and polybutadiene rubber vulcanizates

The rheometric, mechanical, and dynamic mechanical properties as well as fracture surfaces of natural rubber–mica and polybutadiene rubber–mica vulcanizates were studied. Mica was used in the range of 0–30 phr and the rheometric study was carried out at 160°C. The results indicate that the mechanical properties are improved as filler addition increases. Dynamic mechanical testing was used to analyze the observed mechanical behavior. The two elastomers showed different fracture behaviors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2156–2162, 2003     

Hysteresis loss in filled rubber vulcanizates and its relationship with heat generation

A relationship between heat generation of filled rubber vulcanizates and hysteresis loss, specific heat, thermal conductivity, modulus, filler loading, structure, and surface area of the filler, the temperature difference between application temperature and glass transition temperature, frequency, temperature difference between the wall and the environment, stress, and stroke amplitude were developed. Styrenebutadiene rubber (SBR) and natural rubber (NR) vulcanizates were used that had variations of loading of carbon black, silica, resin and coupling agent, types of filler, level of curatives, and cure time. The derived equation was verified with a set of a few unknown SBR and NR vulcanizates, and also by varying the stress and stroke amplitudes in the heat generation experiment. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1541–1555, 1997     

Temperature dependence of birefringence for strained natural rubber vulcanizates

The birefringence for uniaxially extended DCP-cured natural rubber was measured in the temperature range of 213K–353K. The variation of birefringence reflected the changes of the network structure, i.e. the development and disappearence of strain-induced crystals, and the degree of the orientation of amorphous network chains. It became clear from the variation of birefringence that the nucleation condition which is required to allow growth of an extended chain crystal occurred at extension ratio of 2.5–3.5.     

Improving oxidation stability and mechanical properties of natural rubber vulcanizates filled with calcium carbonate modified by gallic acid

A novel technique to modify the surface of calcium carbonate (CaCO₃) nanoparticles, used as an antioxidant and reinforcing filler, by gallic acid is disclosed. The new properties of the modified CaCO₃ could make it more useful and practical for the rubber industry. Thermal gravimetric (TGA), Fourier transform infrared spectroscopy, and transmission electron microscopy analyses showed that the gallic acid was bound onto the surface of CaCO₃. The gallic acid modified CaCO₃ exhibited a significant antioxidation property, as revealed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) analysis. The mechanical properties of natural rubber vulcanizates filled with the gallic acid modified CaCO₃ showed an enhanced reinforcement with increasing loading levels, and increased resistance to ozonolysis over that seen with the unmodified CaCO₃ mixed with Irganox 1010 as the commercial antioxidant.     

Insights into the compatibility of vegetable-based plasticizers on the performance of filled rubber vulcanizates

Substitution of petroleum-based processing oils with eco-friendly sustainable plasticizers in rubber compounds has gained much global attention due to their toxicity. In this regard, so far, the major attempts have focused on substituting aromatic oils with fatty acid based vegetable oils. In this work, the chemical and physical effects of canola oil as a model of fatty acid based vegetable oils on the process-ability, vulcanization kinetics, and final properties of carbon-black filled styrene–butadiene rubbers are systematically investigated. In contrast to the previous studies, it was shown that although these types of vegetable oils have a plasticizing impact, they can indeed threaten the requirements of reinforcing criteria in rubber vulcanizates. The final properties of the vulcanizates were found to be deteriorated due to the incompatibility of canola oil fatty acids constituents with rubber matrix and especially as a result of chemical interference of their unsaturated bonds in sulfur vulcanization kinetics.