Influence of graphene functionalized with zinc dimethacrylate on the mechanical and thermal properties of natural rubber nanocomposites

An effective approach is developed to synthesize zinc dimethacrylate functionalized graphene (ZDMA‐GE) as reinforcing nanofiller for natural rubber (NR). The morphology and structure of ZDMA‐GE were characterized to confirm the exfoliation and functionalization of GE. The as‐prepared nanocomposites were investigated by transmission electron microscopy, mechanical analysis, crosslinked network analysis, and the analysis of thermal conductivity. The results demonstrated that there is strong interfacial interaction between GE and rubber matrix due to good dispersion and special two‐dimensional structure of GE. The crosslink density of the nanocomposites is greatly improved with the introduction of ZDMA‐GE because of the homopolymerization and graft polymerization of ZDMA. It is also noticed that the tensile strength, tear strength, and modulus at 300% elongation of NR nanocomposites with 15 phr ZDMA‐GE have been improved by 133, 42, and 174%, respectively. The thermal conductivity of nanocomposites with 40 phr ZDMA‐GE is enhanced 1.3 times as that of the pure NR. This remarkable improvement is attributed to the formation of covalent crosslinked network and ionic crosslinked network, good dispersion of GE, and efficient interfacial interaction between GE and NR matrix. This method provides the potential applications of functionalized GE in the polymer composites. POLYM. COMPOS., 36:1775–1785, 2015. © 2014 Society of Plastics Engineers     

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     

Effect of crosslink structures on dynamic mechanical properties of natural rubber vulcanizates under different aging conditions

The effects of crosslink structures on the dynamic mechanical properties (DMPs) of unfilled and carbon black N330‐filled natural rubber (NR) vulcanizates cured with conventional (CV), semiefficient (SEV), and efficient (EV) cure systems and having about the same total crosslink densities were investigated before and after aerobic and anaerobic aging at 100°C. The three unfilled NR vulcanizates cured with the CV, SEV, and EV systems had about the same mechanical loss factor (tan δ) values at about 0°C but showed some apparent differences in the tan δ values in the order EV > SEV > CV at relatively high temperatures of 40–80°C before aging. However, N330‐filled NR vulcanizates gave higher tan δ values than the unfilled vulcanizates and showed little effect of the crosslink types on the tan δ at different temperatures over the glass‐transition temperature (T_g) before aging. Aerobic heat aging increased the T_g and tan δ values of the vulcanizates over a wide range of temperatures from ?80 to 90°C that was mainly due to the changes in the total density and types of crosslinks. The unfilled vulcanizates cured with the CV system showed the greatest change in DMP because of their poor resistance to heat aging. Aerobic heat aging of NR vulcanizates caused a more significant change in the DMP than anaerobic heat aging because of the dominant effect of the oxidative degradation during aerobic heat aging on the main‐chain structure, crosslink structures, and DMPs of the vulcanizates. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 710–718, 2001     

Thermal stability and aging characteristics of (natural rubber)/(waste ethylene‐propylene‐diene monomer terpolymer) blends

Comparative studies of the thermogravimetric analysis and thermo‐oxidative aging of (natural rubber)/(waste ethylene‐propylene‐diene monomer terpolymer) (NR/W‐EPDM) and (natural rubber)/(ethylene‐propylene‐diene monomer terpolymer) (NR/EPDM) blends were carried out. The blends were prepared at five different blend ratios (90/10, 80/20, 70/30, 60/40, and 50/50) on a two‐roll mill. As the pure EPDM or W‐EPDM content in the blends increased, their thermal stability also increased. The thermo‐oxidative aging of these blends was done at 100°C for 48 h. Afterwards, the NR/EPDM blends exhibited better retention of properties than the NR/W‐EPDM blends. Crosslink density measurements of the blends after thermal aging indicated that higher crosslink density was obtained from a higher content of EPDM or W‐EPDM, a result which might be due to the high rate of radical termination leading to crosslinks in the bulk of the polymer. J. VINYL ADDIT. TECHNOL., 20:99–107, 2014. © 2014 Society of Plastics Engineers     

Influence of rubber and fabric cord on deformation of a fabric cord-inserted rubber composite by thermal aging

NR composite and PET cord-inserted NR composite were prepared to investigate the contribution level for permanent deformation of fabric cord-inserted rubber composite by thermal aging. The degree of deformation of the PET cord-inserted NR composite was much larger than that of the NR composite without cord. The level of the contribution of the PET cord part on the permanent deformation was much larger than that of the rubber part for the thermal aging below 70 °C. The experimental results were explained by the increased crosslink density change of the rubber part and increased crystallinity of the PET cord part.     

Stress softening of NR reinforced by in situ prepared zinc dimethacrylate

The stress softening effect of nature rubber (NR) reinforced by in situ prepared zinc dimethacrylate (ZDMA) was studied. Degree of stress softening effect (Ds) in the 4th stress–strain cycle of the NR with 10 phr (parts per hundreds of rubber) ZDMA was only 2.23 (strain = 100%), whereas it reached to 59.98 at 50 phr ZDMA (strain = 200%). The stress softening effects of carbon black filled into NR, and compared with the ZDMA effect, was also studied here. Mooney–Rivlin semiempirical equation was introduced here to analysis the stress–strain behavior of the NR vulcanize filled with in situ prepared ZDMA, and the results showed that the ZDMA/NR system has an obvious Payne effect which is in good agreement with the stress softening effect. Crosslink density analysis indicated a high ionic crosslink density in the NR filled with high content ZDMA, which contributed to the low elastic recovery of the stress softening. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High temperature vulcanization of elastomers: 2. Network structures in conventional sulphenamide-sulphur natural rubber vulcanizates

A natural rubber (NR) gum mix with a conventional N-cyclohexyl-2-benzothiazylsulphenamide (CBS) accelerated sulphur system (0.5:2.5 CBS/S) was vulcanized at temperatures from 140°C to 200°C. The influence of cure temperature on (a) the chemical crosslink density, (b) the distribution of crosslink types, (c) the extent of sulphidic main-chain modifications, and (d) the zinc sulphide formation was investigated. Results show that elevated cure temperatures produce a network with a lower crosslink density, in particular a lower polysulphidic crosslink density. The formation of intramolecular sulphidic groups and zinc sulphide increases with increasing temperatures. The possibility of chain scission during vulcanization was examined by a quantitative analysis of the sol-gel data. Less than 1 site of scission per 100 crosslinked isoprene units was established in the temperature range of 140–200°C. The network results can be satisfactorily correlated with the physical properties of a tyre tread mix of NR as reported in Part 1. Mechanistic interpretations are made to account for the network results.     

天然橡胶硫化胶的热氧老化性研究

用热分析法(TGA、DSC)和裂解气相色谱-质谱分析(PGC-MS)研究了天然橡胶硫化胶的耐老化性能及其机理。结果表明,天然橡胶硫化胶的热氧老化初期力学性能和交联密度增加,热失重起始温度上升,随着老化过程的进行,降解效应占优势,硬度和交联密度下降,热氧稳定性变差。其热解机理可能是主链中键的断裂,产物主要是异戊二烯单体和1,4-二甲基-4-乙烯基环己烯。     

Effects of prior aging at 288°C in air and in argon environments on creep response of PMR‐15 neat resin

The creep behavior of PMR‐15 neat resin, a polyimide thermoset polymer, aged in air and in argon environments at 288°C for up to 1000 h was evaluated. Creep tests were performed at 288°C at creep stress levels of 10 and 20 MPa. Creep periods of at least 25‐h in duration were followed by 50‐h periods of recovery at zero stress. Prior isothermal aging increased the elastic modulus and significantly decreased the polymer's capacity to accumulate creep strain. The aging environment had little influence on creep and recovery behaviors. However, aging in air dramatically degraded the tensile strength of the material. Dynamic mechanical analysis revealed an increase in the glass transition temperature from ∼330°C to ∼336°C after 1000 h in argon or in air at 288°C. The rise in the glass transition temperature with aging time is attributed to an increase in the crosslink density of the PMR‐15 polyimide. Increase in the crosslink density due to aging in both air and argon environments is likely behind the changes in the elastic modulus and the decreased capacity for inelastic straining. A visibly damaged surface layer of ∼0.16 mm thickness was observed in specimens aged in air for 1000 h. Results indicate that the unoxidized core material governs the overall mechanical response, whereas the oxidized surface layer causes a decrease in tensile strength by acting as a crack initiation site and promoting early failures. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reinforcement of EPDM by in situ prepared zinc dimethacrylate

The mechanical properties and crosslink density of peroxide‐cured ethylene‐propylene‐diene rubber (EPDM) reinforced with zinc dimethacrylate (ZDMA) were studied. ZDMA was in situ prepared in EPDM matrix through the neutralization reaction of zinc oxide (ZnO) and methacrylate acid (MAA). The effect of ZnO/MAA amount and molar ratio of ZnO/MAA on the properties of the EPDM vulcanizate were investigated in detail. The experimental results showed that EPDM can be greatly reinforced by ZDMA. The excess amount of ZnO considerably increases the tensile strength of the EPDM vulcanizate to reach as high as 37 MPa, whereas its elongation at break keeps over 350%. The process of in situ formation of ZDMA in the EPDM compound was verified by WAXD. Such vulcanizate contains both covalent crosslinks and ionic crosslinks. Crosslink density was determined by an equilibrium swelling method. Dependence of crosslink density on the amount and molar ratio of ZnO/MAA was studied and the extraordinary high tensile strength of the EPDM/ZDMA vulcanizate was related to ionic crosslink density. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1339–1345, 2002; DOI 10.1002/app.10112     

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     

ZDMA/NR复合材料的性能研究

以甲基丙烯酸锌（ZDMA）为补强剂,研究硫化剂DCP用量、ZDMA用量和硫化时间对ZDMA/NR复合材料物理性能的影响.结果表明,在硫化剂DCP存在的情况下,ZDMA对NR具有明显的补强作用,ZDMA/NR复合材料的物理性能和耐热空气老化性能明显改善;当ZDMA和硫化剂DCP的用量分别为15和1.5份、硫化时间为1.5t90时,ZDMA/NR复合材料具有较好的综合物理性能.     

Improved mechanical properties and special reinforcement mechanism of natural rubber reinforced by in situ polymerization of zinc dimethacrylate

The peroxide‐cured natural rubber (NR) was reinforced by in situ polymerization of zinc dimethacrylate (ZDMA). The experimental results showed NR could be greatly reinforced by ZDMA. The tensile strength and the hardness of NR/ZDMA composites increased with the content of ZDMA. The reinforcement mechanism was studied further. Both high crosslinking density provided by ionic crosslinking and strain‐induced crystallization improved the mechanical properties. The crosslinking density was determined by an equilibrium swelling method and the crystallization index was measured by Wide‐angle X‐ray diffraction (WXRD). When the amount of ZDMA was high, the ability of strain‐induced crystallization decreased, due to the strong interactions between the rubber phase and the hard poly‐ZDMA (PZDMA) nanodispersions. At the moment, the increasing ionic crosslinking density made up for the effect of the drop of the strain‐induced crystallization, and played a more important role in the reinforcement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Radiation vulcanization of natural rubber with polyfunctional monomers

This study presents the effect of the polyfunctional monomers (PFMs) triallylcyanurate (TAC), triallylisocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPT), ethylene glycol dimethacrylate (EDMA) and zinc diacrylate (ZDA) on the mechanical properties of natural rubber (NR) crosslinked by electron beam (EB) processing. Dependence of mechanical properties and crosslink density on irradiation dose was determined from a dose range of 50 to 200 kGy. The control blends, obtained with benzoyl peroxide as curing agent, were prepared by blending on a laboratory roller and the control sample curing was accomplished on hydraulic press at 160 °C. The results showed an increase in mechanical properties and crosslink density due to the introduction of PFMs. Also, based on the comparison between EB irradiation and dibenzoyl peroxide vulcanization efficiency, the experimental results show that EB irradiation gave the best results.     

Thermal property improvement of ethylene‐octene copolymer through the combined introduction of filler and silane crosslink

In many applications, e.g., wire and cable insulation, hot water pipe, high‐temperature properties of polymer are essential. This article presents the use of silane crosslinking together with the addition of particular filler in improving the thermal and mechanical properties of ethylene‐octene copolymer (EOC). The effects of filler surface characteristics on siloxane network structure developed and final properties of the crosslinked products are discussed. The results show an increase in the decomposition temperature of EOC more than 50°C after modification. Only crosslinked composites are able to withstand the high‐temperature environment of aging test which is beyond the melting temperature of the matrix polymer. The crosslinked composites filled with calcium carbonate show superior properties to those with silica, due to a higher crosslink density and tighter network structure formed. The silane coupling mechanism and the presence of bound polymer on silica surfaces cause difficulties for the crosslink formation in the silica filled systems. However, an advantageous influence of both silane coupling and crosslink reaction in the silica filled composites is seen on the enhanced tensile strength and modulus of the materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Analysis of thermally aged adhesion specimen between precured and uncured rubber sheets

Retreading of tire is closely related with adhesion between precured and uncured rubber sheets. Adhesion specimens between precured and uncured rubber sheets of BR and NR were prepared and thermally aged at 90 °C for 3 days. Organic materials remained in the adhesion sheets were extracted with THF and analyzed using gas chromatography/mass spectrometry (GC/MS). Elemental sulfur (S₈), mercaptobenzothiazole (MBT), antidegradants, and fatty acids were detected as major organic materials remained in the adhesion sheets. Amounts of the organic materials were reduced by the thermal aging and varied with the adhesion specimens of BR/BR, NR/NR, BR/NR, and NR/BR as the precured and uncured rubber sheets. Decrements of the S₈, MBT, and fatty acids in the NR sheet were larger than in the BR one due to the faster cure characteristics of NR. Changes of the adhesion forces and crosslink densities by the thermal aging were measured. Adhesion force of only the precured BR/uncured NR specimen by the thermal aging was enhanced whereas those of the other specimens were reduced. This was explained with the crosslink density changes and migration of the organic materials through the interface of the adhesion specimen.     

Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Change of crosslink density of natural rubber (NR) vulcanizates by thermal ageing at 60 °C has been studied under swollen conditions in solvents to investigate the influence of internal strain applied to the vulcanizate on the crosslink density change. The internal strain was controlled by swelling with various solvents such as n‐hexane, toluene, tetrahydrofuran (THF), methanol and water. The order of degree of the swelling is toluene ≈ THF > n‐hexane > methanol > water. The influence of curing system has been investigated with the vulcanizates cured by the conventional and EV cure systems. After thermal ageing, the apparent crosslink densities of the swollen vulcanizates in n‐hexane, toluene and THF decrease irrespective of the cure systems, while that of the swollen vulcanizate in water increases. For the swollen vulcanizates in methanol, the apparent crosslink density of the vulcanizate with the conventional cure system after thermal ageing increases while that of the vulcanizate with the EV cure system decreases. The decrement of the apparent crosslink density of the vulcanizate after thermal ageing becomes larger and larger upon increasing the internal strain. © 2001 Society of Chemical Industry     

Influence of accelerator/sulphur and co-agent/peroxide ratios in mixed vulcanisation systems on cure characteristics,mechanical properties and heat aging resistance of vulcanised SBR

The influence of accelerator/sulphur and co-agent/peroxide ratios on cure characteristic and vulcanisate properties in mixed vulcanisation of styrene butadiene rubber (SBR) was investigated in this work. Accelerator/sulphur ratio was investigated with three alternative sulphur curing systems, namely conventional, semi-efficient and efficient vulcanisation (EV) systems. Zinc dimethacrylate (ZDMA) was used as a co-agent to enhance the performance of peroxide and to provide ionic linkages. Ionic linkages contributed by ZDMA create bridges between two polymer chains. The ZDMA/peroxide ratio was varied from 2 to 10. The concentration of dicumyl peroxide was held fixed while the ZDMA content was varied. Cure characteristics, mechanical properties, dynamic mechanical properties and heat aging resistance were investigated in relation to the crosslink structure. Increasing the ZDMA/peroxide ratio significantly increased density of ionic linkages, especially in combination with the EV system. The combination of EV system with high ZDMA/peroxide ratio provided the highest ionic crosslink density and the lowest polysulphidic crosslink density: this enhanced the mechanical properties, the dynamic mechanical properties and the thermal stability of SBR vulcanisates.     

Aging behavior and mechanism of bio‐based engineering polyester elastomer nanocomposites

Bio‐based elastomers used in industry have attracted much attention. We prepared bio‐based engineering polyester elastomer (BEE) nanocomposites by mixing bio‐based engineering polyester elastomers with carbon (CB). The CB/BEE nanocomposites were exposed to an artificial weathering environment for different time periods. Both its aging behavior changes and aging mechanism were investigated in this article. The tensile strength retention rates were each above 90% after aging at 100°C and 125°C for 72 h. CB/BEE nanocomposites exhibited good anti‐aging properties. Furthermore, the chemical changes were detected by Fourier transform infrared spectroscopy and differential scanning calorimetry. The crosslink density changes during aging of BEE were determined as well. A plausible aging mechanism of BEE was proposed. It can be concluded that the thermal oxidation process gives priority to further crosslinking in the initial period of aging. As the aging time increases, chain scission becomes the dominant element in the subsequent thermal oxidation process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40862.     

Silane‐crosslinked ethylene–octene copolymer blends: Thermal aging and crystallization study

Thermally stable materials can be achieved by crosslinking. This article presents the thermal aging and thermal energy storage properties of ethylene–octene copolymer (EOR) and low‐density polyethylene (LDPE) blends as affected by silane crosslinking. Fourier transform infrared spectroscopy revealed a similar degree of silane grafting among the various blend compositions. However, the highest crosslink content was observed in EOR, whereas the lowest was found for LDPE. From melting temperature and heat of fusion data, a linear relationship between the amount of the crystalline component and the crosslink content was found. The decrease in crystallinity due to crosslinking was very limited, which implied a high thermal energy storage capacity of the silane‐crosslinked products and their good mechanical properties at room temperature. Furthermore, a strong ability to retain the properties after thermal aging indicated good thermal stability of the materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008