Reinforcement of natural rubber/high density polyethylene blends with electron beam irradiated liquid natural rubber-coated rice husk

Coating of rice husk (RH) surface with liquid natural rubber (LNR) and exposure to electron beam irradiation in air were studied. FTIR analysis on the LNR-coated RH (RHR) exposed to electron beam (EB) showed a decrease in the double bonds and an increase in hydroxyl and hydrogen bonded carbonyl groups arising from the chemical interaction between the active groups on RH surface with LNR. The scanning electron micrograph showed that the LNR formed a coating on the RH particles which transformed to a fine and clear fibrous layer at 20 kGy irradiation. The LNR film appeared as patches at 50 kGy irradiation due to degradation of rubber. Composites of natural rubber (NR)/high density polyethylene (HDPE)/RHR showed an optimum at 20–30 kGy dosage with the maximum stress, tensile modulus and impact strength of 6.5, 79 and 13.2 kJ/m², respectively. The interfacial interaction between the modified RH and TPNR matrix had improved on exposure of RHR to e-beam at 20–30 kGy dosage.     

Effect of maleic anhydride and liquid natural rubber as compatibilizers on the mechanical properties and impact resistance of the NR‐NBR blend

The degree of compatibilization between natural rubber (NR) and acrylonitrile‐butadiene rubber (NBR) was investigated by two different methods. NBR was chemically modified with maleic anhydride in a screw twin mixer with and without reaction initiator, benzoyl peroxide. Also, the effects of molecular weight of liquid natural rubber (LNR) as a compatibilizer were studied. The degree of compatibilization between NBR and NR is determined indirectly through measurements of mechanical properties and impact resistance. The maleic anhydride and benzoyl peroxide concentrations influence the mechanical properties and impact resistance of the blends. Also, the mechanical properties of the blends showed that the molecular weight of LNR played an important role in determing their performance. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of Epoxidation Content of ENR on Morphology and Mechanical Properties of Natural Rubber Blended PVC

This research work has concerned a study on toughness of PVC/natural rubber (NR) blends compatibilized with epoxidized natural rubber (ENR). The aim of this work was to investigate the effect of degree of epoxidation on morphology and mechanical properties of the blends. Epoxidized natural rubber with a variety of epoxidation contents were prepared by reacting the NR latex with formic acid and hydrogen peroxide at various chemical contents. Chemical structure and epoxidation content of epoxidized natural rubber were evaluated by FTIR and ¹H-NMR techniques. After that, three grades of ENR with epoxidation contents of 15, 25 and 42 % (by mole) were further used for blending with PVC and NR in an internal mixer at 60 rpm and at 170 °C. From tensile and impact tests, it was found that tensile elongation and impact strength of the materials remarkably increased with degree of epoxidation. On the other hand, tensile strength and modulus of the materials rarely changed with the epoxidation content. An increase in toughness of the blends with epoxidation content was related to a better molecular interaction between PVC and ENR as suggested by torque-time curves of the materials.     

Reinforcement of Natural Rubber from Hydroxyl-Terminated Liquid Natural Rubber Grafted Carbon Black. I. Grafting of Acyl Chloride Capped Liquid Natural Rubber onto Carbon Black

Abstract

This paper deals with the grafting of acyl chloride capped liquid natural rubber (LNR–COCl) onto carbon black by the reaction of the acyl chloride group with the phenolic hydroxyl group on the surface. LNR–COCl was prepared by the reaction of hydroxyl-terminated liquid natural rubber (HTNR) with adipoyl dichloride. The percentage of grafting was estimated to be 18–21% depending on the grafting temperature and the molecular weight of HTNR used. It increased with an increase in the molecular weight of LNR–COCl. The LNR grafted onto carbon black was investigated by IR spectroscopy and by hydrolysis with a dilute THF solution of KOH. It was shown that LNR grafted onto the carbon black surface with ester bonds.     

Synthesis of natural rubber-g-maleic anhydride and its use as a compatibilizer in natural rubber/short nylon fiber composites

Natural rubber grafted maleic anhydride (NR-g-MAH) was synthesized by mixing maleic anhydride (MAH) and natural rubber (NR) in solid state in a torque rheometer using dicumyl peroxide (DCP) as initiator. Then the self-prepared NR-g-MAH was used as a compatibilizer in the natural rubber/short nylon fiber composites. Both the functionalization of NR with MAH and the reaction between the modified rubber and the nylon fiber were confirmed by Fourier transform infrared spectroscopy (FTIR). Composites with different nylon short fiber loadings (0, 5, 10, 15 and 20 phr) were compounded on a two-roll mill, and the effects of the NR-g-MAH on the tensile and thermal properties, fiber-rubber interaction, as well as the morphology of the natural rubber/short nylon fiber composites were investigated. At equal fiber loading, the NR-g-MAH compatibilized NR/short nylon fiber composites showed improved tensile properties, especially the tensile modulus at 100% strain which was about 1.5 times that of the corresponding un-compatibilized ones. The equilibrium swelling tests proved that the incorporation of NR-g-MAH increased the interaction between the nylon fibers and the NR matrix. The crosslink density measured with NMR techniques showed that the NR-g-MAH compatiblized composites had lower total crosslink density. The glass transition temperatures of the compatibilized composites were about 1 K higher than that of the corresponding un-compabilized ones. Morphology analysis of the NR/short nylon fiber composites confirmed NR-g-MAH improved interfacial bonding between the NR matrix and the nylon fibers. All these results signified that the NR-g-MAH could act as a good compatilizer of NR/short nylon fiber composites and had a potential for wide use considering its easy to be prepared and compounded with the composites.     

Influence of nonrubber components on properties of unvulcanized natural rubber

Low‐protein natural rubber (LPNR) and acetone‐extracted natural rubber (AENR) were prepared in solid form by alkaline treatment and acetone extraction to remove proteins and lipids. The content of proteins and lipids along with gel content were characterized by Fourier‐transform infrared spectroscopy (FTIR) and size exclusion chromatography with multiangle light scattering (SEC‐MALS) analysis. It was found that natural rubber (NR) treatment by alkaline hydrolysis or acetone extraction decreased proteins or lipids along with gel content. Also, having less proteins and lipids changed the network structure from macroaggregates to microaggregates. This resulted in inferior plasticity and poor mechanical, rheological, and dynamic properties. Furthermore, decreased strain‐induced crystallization and storage hardening were confirmed by temperature scanning stress relaxation (TSSR), after removal of proteins and lipids. Therefore, protein and lipid contents together with gel content play essential roles in controlling various properties of unvulcanized NR.     

Thermoplastic elastomer based on high‐density polyethylene/natural rubber blends: rheological,thermal, and morphological properties

Thermoplastic elastomer (TPE) comprising air‐dried sheet or natural rubber (ADS or NR) and high‐density polyethylene (HDPE) was prepared by a simple blending technique. NR and HDPE were mixed with each type of phenolic compatibilizer (HRJ‐10518 or SP‐1045) or liquid natural rubber (LNR) at 180°C in an internal mixer. The mixing torque, shear stress, and shear viscosity of the blends increased with increasing amounts of NR. Positive deviation blend (PDB) for the blends containing active hydroxyl methyl phenolic resin in HRJ‐10518 or dimethyl phenolic resin in SP‐1045 was obtained. PDB was not observed for the blends without the compatibilizers or with LNR. The blends with HRJ‐10518 or SP‐1045 were compatible or partially compatible while the LNR blends were incompatible. In the phenolic compatibilized blends, NR dispersed in the HDPE matrix was found in the NR/HDPE blends of 20/80, 40/60, and 50/50 ratios. HDPE dispersed in NR matrix was obtained in the NR/HDPE blend of 80/20 ratio, and the co‐continuous phase was accomplished in the NR/HDPE blend of 60/40 ratio. The NR/HDPE blend at 60/40 ratio compatibilized with HRJ‐10518 and fabricated by a simple plastic injection molding machine exhibited higher ultimate tensile strength and elongation at break (EB). Incorporation of parafinic oil caused a decreasing tendency in tensile strength with increases in EB. The TPNRs exhibited high elastomeric nature with low‐tension set. Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation of hydrogenated natural rubber with nanomatrix structure

Hydrogenated deproteinized natural rubber (HDPNR) with nanomatrix structure was prepared through graft‐copolymerization of acrylonitrile and styrene onto HDPNR particle in latex stage. Structural characterization of the resulting materials through nuclear magnetic resonance and Fourier‐transform infrared spectroscopy confirmed that acrylonitrile and styrene were grafted onto HDPNR. The weather resistance, thermal properties, mechanical properties, storage modulus, and morphology of the resulting materials were investigated in comparison with those of HDPNR. The obtained result indicated that the graft‐copolymerization of HDPNR with hydrogenation conversion of 60 mol% attained the highest grafting efficiency. Thermal resistance and storage modulus of HDPNR‐graft‐poly (styrene‐co‐acrylonitrile) (HDPNR‐g‐SAN) were superior compared with those of HDPNR and deproteinized natural rubber. This was attributed to the nanomatrix formed in HDPNR‐g‐SAN, which was confirmed through a transmission electron microscope. Ribbed smoked sheet natural rubber exhibited the outstanding mechanical properties and weather resistance when it was mixed with HDPNR‐g‐SAN.     

Morphology and properties of natural rubber with nanomatrix of non‐rubber components

The morphology of natural rubber was observed by transmission electron microscopy. Nanomatrix of non‐rubber components such as proteins and phospholipids was found to be inherently formed in natural rubber, in which natural rubber particles of about 0.5 µm in average diameter were dispersed. The nanomatrix of non‐rubber components disappeared after deproteinization of natural rubber with urea. Stress at break of serum rubber was higher than that of deproteinized natural rubber, while strain at break did not change. When the amount of the non‐rubber components increased, the stress at break became significantly dependent upon the amount of non‐rubber components. Viscoelastic properties of natural rubber were also dependent upon the nanomatrix of non‐rubber components. Storage modulus of natural rubber increased significantly, when the amount of the non‐rubber components increased. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of naturally occurring crosslinking junctions on green strength of natural rubber

The effect of the naturally occurring crosslinking junctions on green strength of natural rubber, isolated from Hevea brasiliensis, was investigated by using rubber extracted from Parthenium argentatum Gray (Guayule) as a model. Guayule rubber and natural rubber were characterized through nuclear magnetic resonance spectroscopy and size exclusion chromatography. The non‐rubber components of Guayule rubber and natural rubber were characterized by Kjeldahl method and Fourier transform infrared spectroscopy. It was found that Guayule rubber contains a much higher amount of fatty acids and their esters while it contains no proteins. The gel content, determined by swelling method, was related to a number of naturally occurring crosslinking junctions of Guayule rubber and natural rubber. The outstanding green strength of natural rubber was attributed to the effect of naturally occurring crosslinking junctions, when stress–strain curve and tensile properties of unvulcanized Guayule rubber were compared with those of unvulcanized natural rubber. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of the thermogenesis mechanism of natural rubber under high speed strain

This work highlights the relationship of crosslink density, entanglement points and various sulfide crosslinks with the thermogenesis properties of natural rubber (NR). The impact of cross‐link and entanglement on thermogenesis properties was evaluated by heat build‐up test, swelling behavior, statistical thermodynamic calculation, and classic viscoelastic theory. It was found that cross‐link and entanglement points have “pinning” effect to the rubber chain, thus remarkably restricting the motion of the rubber chain and reducing thermogenesis. Besides, the effects of various sulfide crosslinks and cross‐link length on thermogenesis were compared and discussed varying the sulfur vulcanization system. It was found that the semi‐effective vulcanization system using N‐cyclohexyl‐2‐benzothiazolesulfenamide (CZ) and 2‐Mercaptobenzothiazole (M) has the lowest thermogenesis (bottom temperature rise is 7.5°C, middle is 18.7°C), which on account of combined short crosslink length with high rigid rubber chain (crosslink network dominated by mono‐ and disulfides). As a result, the deformation degree of the rubber chain during curl up‐extension and the thermogenesis are further reduced. Finally, a combination of natural film coagulation and semi‐effective vulcanization system was used to prepare a low thermogenesis NR, in which bottom and middle temperature rise were only 5.0°C and 14.1°C, respectively.     

Investigation of natural rubber composites with addition of montmorillonite fillers using thermal analysis

This paper is devoted to the investigation of the properties of the natural rubber composites prepared using the cation exchanged-montmorillonite fillers. The characteristics of the montmorillonite fillers were studied by Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). These characterized fillers were used to preparation of the natural rubber composites, which were submitted to measurements of dynamic-mechanical thermal analysis (DMTA) and vulcanizing characteristics (M _H, M _L, t _s, t _c(90), R _v) as well as physico-mechanical properties (tensile strength, modulus at 300 elongation—M ₃₀₀, tensibility).     

Preparation and characterization of protein‐free natural rubber

Protein‐free natural rubber was prepared by incubation of natural rubber latex with urea and polar organic solvent in the presence of surfactant. Effect of the polar organic solvent on the removal of the proteins was investigated with respect to chemical affinity and concentration of the solvents. Under a suitable condition, nitrogen content of the deproteinized natural rubber (DPNR) was 0.000 wt%, which was less than that of natural rubber deproteinized with proteolytic enzyme or urea in the presence of surfactant. The removal of all proteins from natural rubber was proved through FT‐IR spectroscopy. Changes in morphology of the DPNR were also investigated by transmission electron microscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

Shape memory natural rubber

Charles Goodyear discovered the vulcanization of natural rubber (NR) 170 years ago and transferred the gooey natural compound into the first representative of an entirely new class of materials; the elastomers. Thenceforth, NR was intensively explored and was used for countless products to date. All the more surprising, it was found recently that NR exhibits superior and unexpected properties whenever it is cross-linked to a degree smaller than 0.4% which is fairly below the commonly used 1%–2%. This article gives a brief overview on the exceptional properties of lightly cross-linked NR, named shape memory natural rubber (SMNR), including the cold programmable shape memory effect, storing of extremely large strain, energy and cold, and its capability to sense and memorize environmental parameters. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1381–1388     

Surface characterization of polybutadiene and natural rubbers oxidized by silver(II)

Silver (II) ion is a powerful oxidizing mediator that was used for surface modification of vulcanized polybutadiene rubber (BR) and natural rubber (NR) through mediated electrochemical oxidation (MEO). Scanning electron microscopy (SEM) pictures showed that surface morphology of the oxidized rubbers was changed so that some cracks and holes appeared on the surface in macroscopic scale. This is possibly due to chain scission caused by alkane group formation which is in turn in accordance with the attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra. The amounts of hydroxyl and carbonyl type surface functional groups were also increased in both oxidized rubbers. The results obtained by atomic force microscopy (AFM) showed that the surface roughness for both rubbers was changed significantly from nano- to micro-scale. Energy dispersive X-ray analysis (EDXA) expresses that surface concentration of atomic oxygen for both BR and NR was increased significantly. Also surface polarity of the treated rubbers was enhanced based on contact angle measurements leading to a higher hydrophilicity. Finally it was found that silver(II) has a somewhat greater oxidation impact on the surface of natural rubber than polybutadiene rubber.     

Experimental test and curve fitting of creep recovery characteristics of modified graphene oxide natural rubber and its relationship with temperature

The creep recovery properties of different graphene-doped rubber and the effect of temperature on them were studied. Doping graphene, especially with the surface functional group or surface microstructure, can significantly improve the creep resistance of natural rubber (NR). The permanent creep of each composite tested under the same conditions for 20 min. Graphene oxide, hydrazine hydrate reduced graphene oxide, and 3-aminopropyltriethoxysilane (APTS) grafted graphene oxide was 33%, 16%, and 51% lower than those filled with carbon black respectively. Four parameter model and Weibull distribution function used to analyze and evaluate the creep and recovery test results of composite rubber. These curve fitting results can adequately describe the influence of different types of nanofillers on the creep and recovery properties of composite rubber. The long-term creep of composites forecasted by the time-temperature superposition principle (TTSP). The results show that graphene doping can improve the creep resistance of the rubber. Besides, graphene oxide and surface-modified graphene oxide had better creep resistance than reduced graphene oxide filled natural rubber. It can see that the interfacial properties between the graphene sheet and the natural rubber matrix play an essential role in the creep and recovery properties of graphene/natural rubber composites.     

Stepwise strain-induced crystallization of soft composites prepared from natural rubber latex and silica generated in situ

Novel biphasic structured in situ silica filled natural rubber composites were focused on their strain-induced crystallization (SIC) behavior from the viewpoint of morphology. The composites were prepared by in situ silica filling in natural rubber (NR) latex using a sol–gel reaction of tetraethoxysilane. Simultaneous time-resolved wide-angle X-ray diffraction and tensile measurements revealed a relationship between the characteristic morphology and tensile stress–strain properties of the composites associating with the SIC. Results showed stepwise SIC behaviors of NR-based composites for the first time. Pure rubber phases in the biphasic structure were found to afford highly oriented amorphous segments and oriented crystallites. The generated crystallites worked as reinforcing fillers together with the in situ silica to result in high tensile stresses of the composites. The observed characteristics are useful for understanding a role of filler network in the reinforcement of rubber.     

Morphology dependence of crystallization of natural rubber in blends

Crystallization of natural rubber (NR) was investigated in different morphology for NR/styrene butadiene rubber (SBR) blend and NR/polystyrene-(b)-polyisoprene (SI)/polystyrene (PS) blend. A purified NR (PC-TE) was prepared from pale crape via transesterification. In the blends, PC-TE formed various morphologies; that is, matrix phase, island phase and continuous phase with a nano-scale, respectively, in dependence upon the ratio of the rubbers. The crystallization rate of the blends was also significantly associated with the morphology of the rubbers.     

POSS nanoparticles as a potential compatibilizer for natural rubber/butadiene rubber blends

In this study, it was aimed to investigate octavinyl‐polyhedral oligomeric silsesquioxane (OV‐POSS) incorporation into natural rubber (NR)/butadiene rubber (BR) elastomer blends as a potential compatibilizer. The effects of OV‐POSS loading levels on the thermal, mechanical, morphological, and dynamic‐mechanical properties of elastomer blends were explored. Fourier‐Transform Infrared Spectrometer (FTIR), Temperature Scanning Stress Relaxation (TSSR), and Differential Scanning Calorimetry (DSC) results revealed the conceivable effect of OV‐POSS nanoparticles in the vulcanization through reacting with sulfur and/or elastomers. Scanning Electron Microscope (SEM), X‐Ray Diffraction (XRD), and tensile test measurements supported the improvement of mechanical properties due to homogeneous dispersion at low loading levels. On the other hand, high amount of OV‐POSS incorporation (7 and 10 phr) resulted in a decrease in mechanical properties, owing to the agglomeration of nanoparticles. According to contact angle and Dynamic mechanical analysis (DMA) results, it could be concluded that OV‐POSS nanoparticles were localized at the interface of the elastomers and enabled the compatibilization of immiscible NR/BR blends.     

Stabilization effect of lignin in natural rubber

A series of carbon black filled natural rubbers containing lignin was tested from the view point of their thermo-oxidative aging. Lignin is biopolymer that belongs to the main components of wood. Mechanical properties and crosslink density of lignin stabilized vulcanisates were measured before and after thermo-oxidative aging for 24, 72, 168, 240 and 408 h at 80 °C. The results were compared with those from NR vulcanisates stabilized with the commercial rubber antioxidant N-phenyl-N-isopropyl-p-phenylene diamine (IPPD). The results obtained show that lignin exerts a stabilizing effect in carbon black filled natural rubber. Its effect is comparable with that of conventional synthetic antioxidant. Moreover, the addition of lignin increased the stabilizing effect of IPPD.