Effect of processing parameters on the vulcanisation of natural rubber using glutaraldehyde

The process ability of vulcanising natural rubber using glutaraldehyde at low temperature has been studied. The main objective of this work is to improve the properties and stability of natural rubber (NR) using glutaraldehyde as a curing agent. In this study, the vulcanised samples were prepared systematically and compared with sulphur cured natural rubber vulcanisates. The influence of mole ratio of ammonia and glutaraldehyde, and the processing parameters (i.e. curing time and temperature) was investigated. The cured NR based on glutaraldehyde exhibited better hardness and thermal properties than that of the NR cured from conventional sulphur system. The experimental results reveal that the properties of glutaraldehyde cured NR can be developed with the proper additives combination and conditions adopted in the preparation. This cured system is very interesting due to it can be used for high temperature industrial applications. Moreover, it eases of processing at low temperature and cost.     

Influence of functional groups on properties of styrene grafted NR using glutaraldehyde as curing agent

Natural rubber grafted polystyrene (NR‐g‐PS) and natural rubber grafted polystyrene‐co‐methyl methacrylate (NR‐g‐P(S‐co‐MMA)) were prepared by emulsion polymerization technique using tert‐BuHP‐TEPA as a redox initiator to improve the thermal and mechanical stability of NR. Additional peaks appear in the Fourier‐transform infrared spectra at 695 and 1,732 cm^?1 confirms the formation of graft polymerization. The existence of functional groups on the grafted NR was also clearly confirmed from the morphology obtained from transmission electron microscopy analysis. The effect of curing on the mechanical and thermal properties of grafted NR has also been studied. Glutaraldehyde was used as the curing agent for the grafted and ungrafted NRs throughout the entire course of investigation. It was found that curing of grafted NR samples enhanced tensile strength, modulus, hardness, and thermal stability. Grafted NR showed the tensile strength values of 12 and 17 MPa for NR‐g‐PS and NR‐g‐P(S‐co‐MMA), respectively. Enhancement in thermal stability of NR was confirmend from the activation energy of degradation calculated based on thermogravimetric analyzer. The value of activation energy for NR (135.13 kJ/mol) was found to be increased to 147.89 kJ/mol (NR‐g‐PS) and 151.6 kJ/mol (NR‐g‐P(S‐co‐MMA)). The overall properties of NR have been strongly affected by the interaction and chain bundling between functional groups present in the grafted copolymer and the unsaturated chains in its structure. J. VINYL ADDIT. TECHNOL., 25:339–346, 2019. © 2019 Society of Plastics Engineers     

Curing characteristics and kinetics of EPDM and EOC compounds in co-vulcanization as blend

Possibility of co-vulcanization of ethylene octene copolymer (EOC) and ethylene propylene diene terpolymer (EPDM) molecules was studied by assessing the curing characteristic and crosslinking kinetics of EOC and EPDM compounds. Regarding curing, the curing characteristics, cure rate index, and the torque difference (M_H − M_L) of the EPDM compound are quite similar to those of the EOC compounds at the curing temperature of 180 °C, especially when the EOC octene comonomer content is 5.9 or 9.7 mol %. The kinetic parameters E _a and k were analyzed. The study showed that EOC with 9.7 mol % octene comonomer content is very suitable for blending with EPDM, as it has crosslinking kinetics similar to the EPDM. This observation confirms the possibility of chemical co-crosslinking at EPDM–EOC interfaces, especially at the curing temperature of 180 °C. Differential scanning calorimetry and dynamic mechanical analysis were also used to assess interfacial crosslinking. The lowest activation energy of vulcanization is found for the EPDM/EOC blend with 9.7 mol % octene comonomer contents. Furthermore, chemical co-crosslinking in combination with chain flexibility in the EPDM/EOC blend with 9.7 mol % octene comonomer contents give lower tan δ at room temperature than for the blends with octene comonomer contents of 5.9 and 16.9 mol %. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47613.     

Fabrication and characterization of flexible piezoelectric composites with natural rubber matrix

Abstract

This work aims to fabricate and characterize flexible piezoelectric composites with natural rubber (NR) matrix. Different amounts of Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMNT) powders were added in NR matrices. Porosity, tensile strength and percent elongation at break of composites tended to decrease with increasing PMNT content. The dielectric constant of the NR materials was found to be 3.5. It was raised up to 4.2, 5.0, 4.5, 4.8 and 5.1 when 60, 80, 100, 120 and 150 phr PMNT powders were added. However, dielectric loss of NR materials did not change with PMNT additions. Among this composite system, the NR/100PMNT composite showed the best piezoelectric properties, which its output voltage, piezoelectric coefficient (d₃₃) and piezoelectric voltage coefficient (g₃₃) values were equal to 1.61 V, 2.1?×?10^?4 pC/N and 5.4?×?10^?6 V?m/N, respectively. This composition composite is a promising material suitable for further improvement to be used as piezoelectric generators in energy harvesting applications.     

From a laboratory to a pilot scale production of natural rubber grafted with PMMA

Graft copolymers of natural rubber and poly (methyl methacrylate) (NR‐g‐PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.5 l. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50°C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR‐g‐PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and ¹H‐NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of ¹H‐NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of Chemical Treatment on Thermal Decomposition and Crystallite Size of Coir Fiber

Coir fibers were treated with sodium hydroxide (NaOH) and glutaraldehyde (GA). The influence of alkali and aldehyde treatment on thermal degradation and crystallinity of coir fiber was studied in detail. Thermogravimetric analysis and X-ray diffraction techniques were mainly used to characterize the coir samples. Activation energy of degradation was calculated from Broido and Horowitz–Metzger equations. NaOH-treated samples showed an increase in thermal stability. Removal of impurities such as waxy and fatty acid residues from the coir fiber by reacting with strong base solution improved the stability of fiber. Crosslinking of cellulose with GA in the fiber enhanced the stability of the material. Scanning electron microscopy was employed to analyze the change in surface morphology upon chemical treatment. Improvement in the properties suggests that NaOH and GA can be effectively used to modify coir fiber with excellent stability.     

Novel thermoplastic natural rubber based on thermoplastic polyurethane blends: influence of modified natural rubbers on properties of the blends

Three different forms of natural rubber: maleated natural rubber (MNR), epoxidized natural rubber (ENR) and natural rubber-graft-poly(methyl methacrylate) (NR-g-PMMA) were prepared. Degree of functional groups in rubber molecules was quantified using the integrated peak areas of ¹H NMR. It was found that the modified rubbers with similar level of functionality had been successfully prepared. Thermoplastic natural rubber (TPNR) based on blending of thermoplastic polyurethane (TPU) and various forms of rubber were then prepared using melt blending method. The properties of the blends were studied and compared together in relation to different types of natural rubbers prepared (i.e., unmodified NR, MNR, ENR and NR-g-PMMA). It was found that the blends with modified NR exhibited superior stiffness, entropy effect and damping factor compared to other blends with unmodified NR. This is attributed to the chemical interaction between the functional groups of modified NR molecules and polar functional groups in TPU molecules which facilitated higher interfacial adhesion between both phases. The chemical interaction was verified by ATR-FTIR and TSSR techniques. It was also found that the MNR/TPU blend showed the highest tensile modulus, mechanical and elastic properties with smallest and finer grain dispersion of co-continuous phase compared to ENR/TPU, NR-g-PMMA/TPU and unmodified NR/TPU blends, respectively. This might be due to higher chemical interactions between MNR and TPU phases. Furthermore, the incorporation of rubber did reduce hardness (i.e., <60 Shore A) with improvement of elasticity of the blends compared with the original TPU (i.e., ~85 Shore A).