Mechanical,thermal, morphological,and curing properties of geopolymer filled natural rubber composites

The main objective of this work was to investigate influence of natural rubber (NR) types on mechanical, thermal, morphological, and curing properties together with relaxation behavior of geopolymer filled NR composites with and without bis(triethoxysilylpropyl) tetrasulfide (TESPT) silane coupling agent. Three alternative types of NR: unmodified NR, and epoxidized NR with 25 (ENR-25) or 50 mol % epoxide (ENR-50) were exploited. Rubber compounds filled with GP particles were prepared in an internal mixer at 60 °C and 130–150 °C for the ones with and without TESPT, respectively. It was found that incorporation of GP significantly affected cure characteristics and mechanical properties of the rubber composites. That is, decreasing cure time was observed from 11.6, 3.2, and 7.0 min in gum NR, ENR-25, and ENR-50 to 6.9, 2.1, and 5.0 min in NR/GP, ENR-25/GP, and ENR-50/GP compounds, respectively. Furthermore, the ENR-25/GP and ENR-50/GP composites showed finely dispersed GP particles which indicate high filler–rubber interactions. The in situ silanization with TESPT in rubber composites enhanced the mechanical properties of NR/GP and ENR-25/GP composites but no such enhancement was found in the ENR-50/GP composite. This matched the observations of Payne effect, maximum tan δ, and stress relaxation properties of the composites. We found that the ENR-25/GP composites exhibited the best overall properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47346.     

Role of geopolymer as a cure activator in sulfur vulcanization of epoxidized natural rubber

Geopolymer (GP) was synthesized and used as activators in sulfur vulcanization of epoxidized natural rubber (ENR). Influences of GP on cure characteristics, crosslink density, mechanical, thermal, and morphological properties were investigated and compared to the conventional rubber formulation with ZnO activator. The ZnO is a hazardous chemical for the environment and has proclaimed that its application in rubber technology should be reduced and controlled. It was found that the GP-activated ENR compounds showed significantly higher vulcanization rate than cases with the conventional ZnO compound. This was indicated by the GP activated compounds having shorter scorch time, cure times, and lower activation energy but higher cure rate index (CRI). Also, the GP activated ENR compounded with stearic acid exhibited the highest conversion. This matches well the highest torque difference and crosslink density, observed by temperature scanning stress relaxation (TSSR) and swelling measurements. Furthermore, the GP-activated vulcanizate had better thermal stability than the ZnO-activated ENR material. In addition, the GP-activated ENR vulcanizate with stearic acid exhibited high 100% moduli, tensile strength, and hardness. This proves that GP has a high potential for use as activators in sulfur vulcanization of rubber compounds, as an alternative to the conventional ZnO. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48624.     

Novel ternary blends of natural rubber/linear low-density polyethylene/thermoplastic starch: influence of epoxide level of epoxidized natural rubber on blend properties

Novel degradable materials based on ternary blends of natural rubber (NR)/linear low-density polyethylene (LLDPE)/thermoplastic starch (TPS) were prepared via simple blending technique using three different types of natural rubber (i.e., unmodified natural rubber (RSS#3) and ENR with 25 and 50 mol% epoxide). The evolution of co-continuous phase morphology was first clarified for 50/50: NR/LLDPE blend. Then, 10 wt% of TPS was added to form 50/40/10: NR/LLDPE/TPS ternary blend, where TPS was the particulate dispersed phase in the NR/LLDPE matrix. The smallest TPS particles were observed in the ENR-50/LLDPE blend. This might be attributed to the chemical interactions of polar functional groups in ENR and TPS that enhanced their interfacial adhesion. We found that ternary blend of ENR-50/LLDPE/TPS exhibited higher 100 % modulus, tensile strength, hardness, storage modulus, complex viscosity and thermal properties compared with those of ENR-25/LLDPE/TPS and RSS#3/LLDPE/TPS ternary blends. Furthermore, lower melting temperature (T _m) and heat of crystallization of LLDPE (?H) were observed in ternary blend of ENR-50/LLDPE/TPS compared to the other ternary blends. Also, neat TPS exhibited the fastest biodegradation by weight loss during burial in soil for 2 or 6 months, while the ternary blends of NR/LLDPE/TPS exhibited higher weight loss compared to the neat NR and LLDPE. The lower weight loss of the ternary blends with ENR was likely due to the stronger chemical interfacial interactions. This proved that the blend with ENR had lower biodegradability than the blend with unmodified NR.     

Comparative study of the elasticity and permeability of vulcanized films made with skim and cream natural rubber latex

The purpose of this study was to gain a clearer picture of the structure and properties of vulcanized films made with skim and cream latex from Hevea brasiliensis. The two properties targeted for this study were the elasticity of the films and their permeability to acetone. Surface characterization by atomic force microscopy revealed that vulcanization substantially modified the structure of the films compared to unvulcanized films. Unlike unvulcanized films, particle identity was retained in the vulcanized films made with cream latex, even after 4 weeks of aging. In addition, skim latex gave vulcanized films with greater elasticity than those obtained with cream latex. On the basis of the structural characterization carried out on the latex and films and information from the literature, the greater elasticity of the skim films arose from more entanglements between polyisoprene chains and associations between proteins. Despite differences in the structure, the acetone permeability was very similar for skim and cream vulcanized films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimizing mechanical and morphological properties of biodegradable thermoplastic elastomer based on epoxidized natural rubber and poly(butylene succinate) blends

Biodegradable thermoplastic elastomer (BTPE) blends of epoxidized natural rubber (ENR) and poly(butylene succinate) (PBS) were prepared by the melt mixing process. Influences of the processing parameters mixing temperature, rotor speed, and mixing time on mechanical and morphological properties of BTPE were investigated. Taguchi method was applied to improve the mechanical and morphological properties by optimizing the processing parameters. That is, the experimental design adopted the L9 Taguchi orthogonal array with three manipulated factors (i.e., mixing temperature, rotor speed, and mixing time). Analysis of mean and analysis of variance were also exploited and the mixing temperature was found to be the most significant processing parameter regarding mechanical properties. The mixing temperature showed large contributions to Young's modulus, 100% modulus, tensile strength, and elongation at break, namely 45.33, 40.38, 49.31, and 36.04%, respectively. Furthermore, the optimum conditions found for mixing temperature, rotor speed, and mixing time were 140 °C, 100 rpm and 10 min, respectively. The result was confirmed by atomic force microscopy and scanning electron microscopy micrographs showing fine‐grained co‐continuous phase morphology of the ENR/PBS blends. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46541.     

SEC‐MALS study of dynamic structuring of natural rubber: Comparative study of two Hevea brasiliensis genotypes

The dynamic structuring of natural rubber (NR) was studied selecting two specific Hevea brasiliensis genotypes (RRIM600 and PB235) to prepare model samples. The mesostructure (macromolecular structure + aggregates or gel) of NR samples was studied by SEC‐MALS. The NR samples were analyzed after (i) slow structuring (18 months' storage at room temperature) and (ii) fast structuring (stored for 24 h on P₂O₅ at 60°C). This study showed that the macromolecular structure, especially M_n, and the total gel rates were dramatically modified after fast structuring. For genotype RRIM600, the aggregates formed during fast structuring were essentially macroaggregates, whereas for genotype PB235 mostly microaggregates were formed. These results indicate that the dynamic structuring of NR is dependent on genotype. Depending on the genotype, for extreme conditions (fast structuring), it can be assumed there was percolation between elementary bricks, probably microaggregates, or no percolation. Although the mechanisms of dynamic structuring are quite complex and should be multifactors dependent, on the basis of our results, the degree of percolation seems to be partly dependent on the quantity of short polyisoprene chains initially present in the NR samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012