Studies on xanthate/dithiocarbamate accelerator combination in NR/BR blends

Zinc butyl xanthate [Zn(bxt)₂] was prepared in the laboratory. The effect of this xanthate with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of natural rubber (NR), polybutadiene rubber (BR), and NR/BR blend has been studied at different temperatures. The amounts of Zn (bxt)₂ and ZDC in the compounds were optimized by varying the amount of ZDC from 0.75 to 1.5 phr and Zn (bxt)₂ from 0.75 to 1.5 phr. The cure characteristics were also studied. HAF filled NR, BR, and NR/BR blend compounds were cured at different temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density and elongation at break, compression set, abrasion resistance, etc. were evaluated. The results show that the mechanical properties of 80NR/20BR blends are closer to that of NR vulcanizates, properties of 60NR/40BR blends are closer to BR vulcanizates, while the 70NR/30BR blends show an intermediate property. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3516–3520, 2007     

炭黑/煤矸石/碳纳米管复合填料体系对天然橡胶性能的影响研究*

利用硝酸氧化法对碳纳米管(CNTs)进行纯化,并用环氧天然橡胶(ENR)进行改性处理。结合胶质量分数测定结果表明, ENR用量15%(质量)时效果最佳。采用胶乳凝聚法制备CNTs/天然橡胶(NR)母料。煤矸石粉(CG)经高温煅烧和表面改性处理。 将CNTs/天然橡胶(NR)母料、CG和炭黑(CB)通过机械混炼法与天然橡胶及配合剂混合,制备CB/CG/CNTs/NR复合材料,并对复合材料进行硫化特性及物理机械性能。结果表明： CNTs延迟硫化效应明显;相比炭黑,CG对硫化具有促进作用。硫化特性和甲苯溶胀法测定结果表明,在填料份数相同的条件下,单独由CB填充的NR有最大的交联密度,CNTs对交联密度影响不明显。物理机械性能测试结果表明,当CG：CB：CNTs=17.5:16.5:1(Phr)时,NR硫化胶的300%定伸应力和扯断伸长率明显高于单独由CB填充NR,而拉伸强度与之接近,复合填料样填充NR具有较好的综合性能。扫描电镜测试结果表明,复合填料在NR基体中分布均匀。     

New approach for preparation of dry natural rubber nanocomposites through acid‐free co‐coagulation: Effect of organoclay content

Natural rubber (NR) vulcanizates exhibit good mechanical properties compared to vulcanizates of synthetic rubbers. Incorporation of a conventional filler at higher loadings to NR enhances its modulus, while reduction in tensile strength and elongation. This paper presents a new strategy for development of a NR‐clay nanocomposite with enhanced mechanical properties by incorporation of lower loadings (2–8 phr) of cetyl trimethyl ammonium bromide modified montmorillonite clay (OMMT‐C) under acid‐free environment. The effect of OMMT‐C loading on cure characteristics, rubber‐filler interactions, crosslink density, dynamic mechanical thermal properties, and mechanical properties were evaluated. Incorporation of OMMT‐C accelerated the vulcanization process and enhanced mechanical properties. X‐ray diffraction analysis and scanning electron microscopy images revealed that the formation of intercalated clay structures at lower OMMT‐C loadings, and clay aggregates at higher loadings. A nanocomposite at OMMT‐C loading of 2 phr exhibited the best balanced mechanical properties, and was associated with highest crosslink density and rubber–filler interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46502.     

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%.     

Effect of ionic liquids and surfactants on zinc oxide nanoparticle activity in crosslinking of acrylonitrile butadiene elastomer

The goal of this work was to study the influence of several ionic liquids and cationic surfactants on zinc oxide nanoparticle activity in sulfur vulcanization of acrylonitrile butadiene elastomer (NBR). In this article, we discuss the effect of ionic liquids and surfactants on the cure characteristics, crosslink density, and distribution in the elastomer network as well as on mechanical properties of the acrylonitrile butadiene rubber. Ionic liquids (alkylimidazolium salts) and cationic surfactants (alkylammonium bromides) decrease the vulcanization time of rubber compounds. Their application results in the increase of vulcanizate crosslink density as well as of the heterogeneity of elastomer network. The influence of ionic liquids on the acrylonitrile butadiene elastomer properties depends on the anion present in the molecule and on the length of alkyl chains attached to the imidazolium ring. The most active ionic liquids seem to be the ones with the 1‐butyl‐3‐methylimidazolium cation or the BF₄^‐ anion. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hydrogenated natural rubber blends: Aspect on thermal stability and oxidative behavior

Hydrogenated natural rubber (HNR) prepared from natural rubber (NR) is a new sustainable elastomer with excellent thermal properties. This study reports on the effect of vulcanization system and blend ratio on the thermal and oxidative resistance of HNR/NR vulcanizates. The various HNR/NR ratios vulcanized by peroxide and sulfur donor system exhibited the highest retention of tensile strength after thermal aging due to the formation of zinc‐dimethyldithiocarbamate (ZDMDC) which is an efficient antioxidant. The results from thermogravimetric analysis (TGA) indicated that the saturated structure of HNR had higher decomposition temperature and activation energy to enhance the thermal stability of HNR/NR vulcanizates. The initial and maximum decomposition temperatures of NR and HNR phases in vulcanizates were not affected by rubber blend ratio. This suggests that the decomposition pattern of HNR has no influence on another constituent. The increase in HNR content in the blends could retard the ozonolysis resulting in the surface cracking attacked by ozone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

OV-POSS改性CM胶料的硫化行为及其硫化胶的性能

将氯化聚乙烯弹性体(CM)与笼型八乙烯基倍半硅氧烷(OV-POSS)进行共混,制备POSS改性CM胶料;采用过氧化二异丙苯(DCP)为硫化剂,三烯丙基异氰脲酸酯(TAIC)为助硫化剂,利用无转子硫化仪对该改性胶料的硫化行为及硫化动力学进行研究。利用动态力学热分析仪(DMA)以及热机械分析仪(TMA)对硫化胶的力学性能、热稳定性能,及其动、静态热机械性能进行了研究。结果表明：随着OV-POSS用量的增加,改性胶料的硫化反应活化能逐步降低,硫化速度加快,硫化胶的拉伸强度、玻璃化温度(T_g)相应提高。表明OV-POSS对CM的硫化具有促进作用,加入OV-POSS,可改善其硫化胶的力学性能以及提高热稳定性能。     

The mechanism of carbon–silica dual phase filler modified by ionic liquid and its reinforcing on natural rubber

The carbon–silica dual phase filler (CSDPF) was modified by ionic liquids (ILs): 1‐allyl‐3‐methyl‐imidazolium chloride (AMI) and 1‐butlyl‐3‐methyl‐imidazolium hexafluorophosphate (BMI). The modified CSDPF was then incorporated into natural rubber (NR) through mechanical mixing. The interactions between CSDPF and ILs were investigated using differential scanning calorimetry (DSC), Fourier‐transform infrared spectroscopy (FTIR), and Raman spectroscopy. The bound rubber of NR compounds, the mechanical properties, and dynamic properties of NR vulcanizates filled with ILs modified CSDPF (ILs‐CSDPF/NR) were measured. The results showed that the AMI interacted with CSDPF through both hydrogen bonds and van der Waals forces, while the interaction between BMI and CSDPF was merely weak van der Waals force. The modification of CSDPF by ILs could improve the tensile strength, tear resistance, and fatigue life of NR vulcanizates. The AMI‐CSDPF/NR gave the superior mechanical and dynamic properties among the NR vulcanizates with the highest bound rubber content and the most homogeneous filler dispersion, which was displayed in scanning electron microscope (SEM) images. POLYM. COMPOS., 36:1721–1730, 2015. © 2014 Society of Plastics Engineers     

Effects of hot‐air aging and dynamic fatigue on the structure and dynamic viscoelastic properties of unfilled natural rubber vulcanizates

The effects of hot‐air aging and dynamic tensile fatigue on the network structure and dynamic viscoelastic properties of unfilled natural rubber (NR) vulcanizates were investigated with magnetic resonance crosslink density spectrometry, Fourier transform infrared spectroscopy/attenuated total reflection (FTIR–ATR), and dynamic mechanical analysis. The results showed that there was a carbonyl weak absorption peak at 1723 cm^?1 in the FTIR–ATR spectra of unfilled NR vulcanizates after hot‐air aging; The crosslink density decreased continuously as the aging time increased. The dynamic modulus of an aged specimen declined considerably, and the value of tan δ after 72 h of aging greatly increased. There was a large difference in the FTIR–ATR spectra of unfilled NR vulcanizates before and after tensile fatigue. The peaks at 1597, 1415, and 1015 cm^?1 increased concurrently with the tensile fatigue time. Initial analysis suggested that structures such as conjugated dienes appeared in the network structure. The modulus declined sharply, whereas the value of tan δ increased noticeably, after tensile fatigue. The effects of hot‐air aging and tensile fatigue on the crosslink density and FTIR–ATR spectra of unfilled NR vulcanizates were different, but both affected the viscoelastic properties dramatically. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

镧配合物对天然橡胶的防老化作用

选用自制的镧配合物,采用常规方法与天然橡胶混合、硫化制得硫化胶,测试了胶料的硫化特性、硫化胶的力学性能,研究了天然橡胶硫化胶的耐热氧老化性能。结果表明:镧配合物的加入,有助于改善天然橡胶的硫化特性;添加镧配合物的硫化胶力学性能有明显提高;硫化胶的热氧老化结果显示,镧配合物的加入对天然橡胶有较好的防老化作用,其防老化效果优于工业常用防老剂4010NA。     

维生素C镧配合物对天然橡胶的防护作用

将自制的维生素C镧配合物（VCLa）作为新型防老剂用于天然橡胶（NR）中,考察VCLa对胶料性能的影响。结果表明：VCLa对NR具有一定的硫化促进作用,显著缩短胶料的t90,略微提高硫化胶拉伸性能;VCLa对NR具有优良的防护作用,其防臭氧老化效果显著优于常用防老剂4010NA,RD和MB,防热氧老化效果与防老剂4010NA和RD相当,优于防老剂MB,防紫外光老化效果接近于防老剂4010NA和RD,但优于防老剂MB;VCLa减缓NR应力老化,提高硫化胶的耐磨性和耐屈挠疲劳性能。     

离子液体与偶联剂并用对白炭黑填充NR性能的影响

本文用偶联剂Si-69、B-69和离子液体[溴化1-丁基-3-甲基咪唑(BMIM)]单独改性白炭黑,同时用两种偶联剂分别与离子液体BMIM并用改性白炭黑,对比研究了其对NR性能的影响。结果表明,与未改性白炭黑相比,Si-69、B-69和BMIM改性白炭黑后,填充NR的硫化速率加快,Payne效应减弱,力学性能改善,滚动阻力降低;其中,BMIM改性白炭黑填充NR的综合性能最优,其拉伸强度和撕裂强度比未改性白炭黑填充NR提高了一倍。与偶联剂单独改性白炭黑相比,偶联剂与BMIM并用改性白炭黑后,填充NR的t90进一步缩短,填料-橡胶相互作用更强,交联密度更大,力学性能进一步提高,滚动阻力变得更低。     

The effect of epoxidized natural rubber on mechanical properties of siliceous earth/natural rubber composites

Siliceous earth (SE) is a kind of mineral consisting of lamellar kaolinite, muscovite (aluminum silicate) and corpuscular silica. Natural rubber (NR) composites containing NR as matrix, epoxidized natural rubber (ENR) as compatibilizer and SE as filler were produced by latex coagulating process and cured using a conventional sulfuric system. Monsanto measurements have shown that the ENR accelerates the vulcanization reaction and gives rise to a marked increase of the torque. The results of physico-mechanical properties of NR vulcanizates show that, when SE modified by silane coupling agent and in the meanwhile adding 4 phr of ENR as compatibilizer, maximum tensile strength, elongation at break, reinforcing index (M300/100) of NR/SE vulcanizates were obtained. The dynamic-mechanical properties exhibit the addition of ENR can enhance wet grip characteristics and reduce rolling resistance by lowering tan δ values at 60 °C and increasing tan δ values at 0 °C of NR compounds. The overall results show that properties of SE-reinforced NR substantially improved by adding ENR as compatibilizer. The addition of silane coupling agent and combining an appropriate amount of ENR would be better choice to improve the properties of NR/SE compounds.     

Effect of a small amount of sulfur on the physical and mechanical properties of peroxide‐cured fully saturated HNBR compounds

Sulfur can be used as crosslink coagent in unsaturated elastomer. In this work, a fully saturated HNBR with 39 wt % nitrile content was selected to investigate the effect of a small amount of sulfur acting as crosslink coagent on the physical and mechanical properties of peroxide‐cured vulcanizates. First, selective cleavage of polysulfide (? Sx? ) and monosulfide(? S? ) bond by combined thiol‐piperidine treatment were performed and the existence of poly/monosulfide bond in sulfur‐contained HNBR compounds was verified. Then, no‐filler HNBR compounds with various content of sulfur were investigated to detect the influence of sulfur on the crosslink density and cure kinetics. The MDR results showed that the crosslink density of HNBR compounds reduced only when the amount of sulfur is 0.25 phr and above. Besides, the curing rate of no‐filler HNBR compounds increased with the increasing of the amount of sulfur and reached a maximum at a dosage of 0.25 phr sulfur. Finally, physical and mechanical properties of fully formulated compounds were evaluated and it was found that the addition of small amounts of sulfur in fully saturated HNBR compounds could improve the dynamic properties of peroxide‐cured HNBR compounds remarkably but at a cost of slightly higher compression set values and a small loss in heat aging resistance. In a conclusion, small amount of sulfur can impart the peroxide vulcanizates some “sulfide properties” like dynamic property, tensile strength, but at the same time, due to the introduction of sulfur, some “peroxide vulcanizates property” like heat‐resistance property, hot air resistance were weakened slightly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41612.     

Influence of rubber composition on change of crosslink density of rubber vulcanizates with EV cure system by thermal aging

Variation of the crosslink density of a rubber vulcanizate depending on the rubber composition after the thermal aging was studied with single rubber, biblend, and triblend vulcanizates of natural rubber (NR), butadiene rubber (BR), and styrene‐butadiene rubber (SBR). The efficient vulcanization (EV) system was employed to minimize the influence of free sulfur in the vulcanizate on the change of the crosslink density. Thermal aging was performed at 40, 60, and 80°C for 20 days with 5‐day intervals. The crosslink densities of the vulcanizates after the thermal aging increase. For the single rubber vulcanizates, variation of the crosslink density by the thermal aging has the order: SBR > BR > NR. For the biblend vulcanizates, variations of the crosslink densities of the NR/SBR and SBR/BR blends are larger than that of NR/BR blend. Variation of the crosslink density of the vulcanizate increases by increasing the SBR content in the vulcanizate. Variation of the crosslink density of the rubber vulcanizate depending on the rubber composition was explained by miscibility of the blends, combination reaction of the pendent groups, and mobility of the pendent group. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1378–1384, 2000     

Chemical crosslink densit and network structure of natural rubber vulcanizates modified with phosphorylated cardnol prepolymer

The chemical crosslink density (CLD) and network structure of natural rubber (NR) vulcanizates, modified with phosphorylated cardanol prepolymer (PCP), have been studied by equilibrium swelling and other chemical methods. The PCP-modified NR vulcanizates showed lower CLD, as compared to the unmodified NR samples, the decrease being lesser for the semiefficient vulcanization (SEV) system, as compared to the conventional (CV) and efficient (EV) vulcanization system. The superior tensile characteristics of the PCP-modified vulcanizates of the SEV system is presumed to be partly due to the presence of an entangled network structure between the aliphatic segment of PCP and the isoprene chains, as evident from X-ray diffraction studies. The critical role of Zn⁺⁺ions in the crosslinking reactions, especially at higher concentrations of PCP, was evident from the increase in CLD at higher concentrations of ZnO. The reduction in the IR absorption intensity, in the presence of ZnO, indicated the probable complex formation of Zn⁺⁺ions with the phosphate groups of PCP. © 1994 John Wiley & Sons, Inc.     

Mechanical properties of deproteinized natural rubber in comparison with synthetic cis‐1, 4 polyisoprene vulcanizates: Gum and black‐filled vulcanizates

Gum and black‐filled vulcanizates having various crosslink densities were prepared from 2 types of rubber, namely, deproteinized natural rubber (DPNR) and synthetic cis‐1, 4 polyisoprene vulcanizates (IR). Their mechanical properties, such as tensile strength, tear strength, abrasion loss, and heat buildup resistance, at various crosslink densities as well as at similar optimum crosslink density were compared. For both gum and black‐filled systems, IR possessed a higher crosslink density than that of DPNR at a fixed curative content. Tensile and tear strength of all vulcanizates passed through a maximum with increasing crosslink density. For gum vulcanizates, tensile and tear strengths of DPNR and IR below the maximum were not much different. However, IR had a narrower tear strength peak relative to DPNR. At a comparable optimum crosslink density, DPNR exhibited higher tensile strength and crack growth resistance than IR. For black‐filled vulcanizates, tensile and tear strengths, and heat buildup resistance of DPNR and IR at a given crosslink density were similar. The results revealed that the properties of gum samples were more dependent upon crosslink density than the black‐filled ones because the reinforcement by carbon black overshadowed the intrinsic properties of the rubbers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1139–1144, 2005     

Interfacial Interactions of Silica and Natural Rubber Enhanced by Hydroxyl Telechelic Natural Rubber as Interfacial Modifier

The incompatibility between hydrophilic silica and hydrophobic rubber is an important problem on using silica in nonpolar rubber. In this study, hydroxyl telechelic natural rubber (HTNR) that contains hydroxyl‐terminated groups was introduced into silica‐reinforced natural rubber (NR) in order to improve the bonding strength between rubber and silica. The properties of silica‐reinforced NR compounds and vulcanizates as a function of varying silica contents were evaluated at a fixed HTNR concentration at 8% wt/wt of silica content. The results show that the improvement of silica dispersion and decreasing of filler–filler interactions (Payne effect) were obtained in the NR compounds and vulcanizates with HTNR addition. The enhancements in tensile properties, crosslink density, abrasion resistance, heat build‐up, and thermal properties of the silica‐reinforced NR vulcanizates with added HTNR confirmed that HTNR performed good as interfacial modifier of silica. In the study, the optimum properties of silica‐reinforced NR vulcanizate were achieved at 30 phr silica with 2.4 phr HTNR. However, HTNR still showed poorer efficiency than the synergy between commercial silane coupling agent, bis [3‐(triethoxysilyl) propyl] tetrasulphide (TESPT) and diphenylguanidine (DPG) when used in silica‐reinforced NR vulcanizate. J. VINYL ADDIT. TECHNOL., 26:291–303, 2020. © 2019 Society of Plastics Engineers     

三种微生物脱硫废乳胶及其填充天然橡胶的力学性能比较

利用三种微生物鞘氨醇单胞菌、脂环酸芽孢杆菌和酵母菌对废乳胶(WLR)进行了脱硫再生,考察了脱硫过程中微生物的生长情况以及脱硫前后WLR溶胀和交联密度的变化,并将WLR和脱硫WLR(DWLR)以不同份数填充到天然橡胶(NR)中,对比了DWLR/NR硫化胶和WLR/NR硫化胶的力学性能和交联密度。结果表明,利用鞘氨醇单胞菌脱硫的WLR溶胀值较高,交联密度较低。随着乳胶用量的增加,填充NR硫化胶的拉伸强度和交联密度逐渐降低,扯断生长率逐渐增加。DWLR/NR硫化胶的力学性能明显优于WLR/NR硫化胶,且鞘氨醇单胞菌脱硫的DWLR/NR的力学性能明显优于其它两种微生物脱硫的DWLR/NR硫化胶。     

Effect of vulcanizing system on the crosslink density of nitrile rubber compounds

The synergistic activity of binary accelerator systems in rubber vulcanization is well known. Binary accelerator systems are being widely used in industry and are becoming increasingly popular because of the fact that such mixed systems can produce a vulcanizate with superior mechanical properties compared to those of stock cured with a single accelerator. The authors have studied the performance of a binary accelerator system based on cyclohexyl benzothiazole sulfenamide (CBS), tetramethyl thiuram disulphide (TMTD) in the sulfur vulcanization of nitrile rubber. The amount of sulfur and accelerator was varied to change the network crosslink density of vulcanizates. The observed mutual activity has been discussed based on the mechanical properties and crosslink density. The physical crosslink density of the various nitrile rubber mixes was estimated using the Kinetic Theory of Elasticity. The mechanical properties of the various rubber compounds were related to the corresponding crosslink density estimated for each compound. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2440–2445, 2005