High Ammonia Natural Rubber Research Articles

Preparation and Characterization of Poly(Methyl Methacrylate) Grafted Natural Rubber Latex Films

Poly(methyl methacrylate) (PMMA) grafted natural rubber (NR) latex was successfully prepared and solely exploited even at high MMA concentration (1.5 mol/kg-rubber) to make coherent and uniform vulcanized films without blending with other polymer to achieve excellent physical properties. High ammonia natural rubber (HANR) latex was subjected to graft-copolymerization with methyl methacrylate (MMA) monomer in the presence of tert-butyl hydroperoxide (TBHP) and tetraethylenepentamine (TEPA). High conversion, i.e., 85.12 mol%, and grafting efficiency, i.e., 92.70 mol%, were obtained at 1.5 mol/kg-rubber MMA. The resulting gross PMMA grafted NR (1.5PMMA) latex was then compounded, dipped, and vulcanized to produce thin films. The tensile strength and modulus at 300 percent (M300) of vulcanized 1.5PMMA film were superior to vulcanized HANR film by 1-fold. While elongation at break (EB) was identical to each other due to the high gel content in both vulcanized films. Besides, the vulcanized 1.5PMMA film absorbed less oil compared to HANR film. The thermal stability of vulcanized 1.5PMMA film was found to be higher than that of vulcanized HANR film. Hence, it can be deduced that controlling the graft-copolymerization of PMMA in NR latex is the key to produce coherent thin films with improved properties at higher PMMA content.

Influence of Centrifugation Cycles of Natural Rubber Latex on Final Properties of Uncrosslinked Deproteinized Natural Rubber.

Natural rubber latex (NRL) is a polymer (blend) extracted from the milky sap of para rubber trees. Due to being a natural biopolymer, NRL contains various proteins that may be allergenic to humans when in skin contact. Attempts have been made to use deproteinized natural rubber (DPNR) instead of impure NRL, and the final properties of these two types of rubber tend to differ. Thus, the correlations between their chemistry and properties are of focal interest in this work. DPNR was prepared by incubating NRL with urea, followed by aqueous washing/centrifugation. The physical, mechanical, and dynamic properties of incubated NRL before and after washing/centrifugation were examined to distinguish its influences from those of incubation with urea. According to the findings, the proteins, phospholipids, and chain entanglements were responsible for natural polymer networks formed in the NR. Although the proteins were largely removed from the latex by incubation, the properties of high ammonia natural rubber (HANR) were still maintained in its DPNR form, showing that other network linkages dominated over those contributed by the proteins. In the incubated latex, the naturally occurring linkages were consistently reduced with the number of wash cycles.

Preparation and characterization of self-healing natural rubber latex film

The objective of this study was to prepare and characterize the self-healing natural rubber latex films with different zinc thiolate (ZT) content. In this work, ZT was introduced into high ammonia natural rubber latex (HANRL) through a peroxide vulcanization system at different ZT content (0, 15, 30, 45 phr). The self-healing strategy is based on reversible ionic interaction between Zn2+ ion and S- ion in ZT cross-linker. Evidence for the presence of reversible ZT ionic networks was provided by Fourier-transform infrared spectroscopy (FTIR) analysis. The results revealed that HNRL/DCP/30ZT able to recover its initial properties after the broken sample was brought in contact with each other. The healing efficiency for tensile strength, elongation at break and tear strength were obtained at 93.77%, 98.77% and 89.50%, respectively.

A model study on the impact of metal ions on pre-vulcanization of concentrated natural rubber latex and dipped-products

A model study on the influence of some heavy metal ions on the stability and vulcanization efficiency of uncompounded and compounded high-ammonia natural rubber (HANR) latex was carried out by an exogenous addition and then determined by Brookfield viscometer, mechanical stability time (MST) tester, and tensile testing machine. The case of pre-vulcanized HANR latex with different aging times was determined by the change in the volatile fatty acid (VFA) number, MST, and viscosity. The compounded HANR latex was coagulated by adding Mn2+and Mg2+ while it was unaltered by adding Zn2+, Fe2+, and Cu2+ ions, leading to their colloidal stability. Therefore, these metal ions were chosen further to study the pre-vulcanization of compounded HANR latex. The presence of Zn2+, Fe2+, and Cu2+ in the latex is responsible for the delay in the vulcanization process and changes the appearance of compounded latex. Before compounding, the addition of such metal ions led to the reduction in tensile strength of the obtained gloves. At the same time, there was no effect on the tensile properties of the gloves made from the compounded HANR latex containing the metal ions.

Enhanced adsorptive composite foams for copper (II) removal utilising bio-renewable polyisoprene-functionalised carbon derived from coconut shell waste

A bio -renewable polyisoprene obtained from Hevea Brasiliensis was used to produce functionalised carbon composite foam as an adsorbent for heavy metal ions. Functionalised carbon materials (C-SO3H, C-COOH, or C-NH2) derived from coconut shell waste were prepared via a hydrothermal treatment. Scanning electron microscopy images showed that the functionalised carbon particles had spherical shapes with rough surfaces. X-ray photoelectron spectroscopy confirmed that the functional groups were successfully functionalised over the carbon surface. The foaming process allowed for the addition of carbon (up to seven parts per hundred of rubber) to the high ammonia natural rubber latex. The composite foams had open pore structures with good dispersion of the functionalised carbon. The foam performance on copper ion adsorption has been investigated with regard to their functional group and adsorption conditions. The carbon foams achieved maximum Cu(II) adsorption at 56.5 {text{mg g}}_{text{foam}}^{-1} for C-SO3H, 55.7 {text{mg g}}_{text{foam}}^{-1} for C-COOH, and 41.9 {text{mg g}}_{text{foam}}^{-1} for C-NH2, and the adsorption behaviour followed a pseudo-second order kinetics model.

Controlling the characteristics of raw natural rubber by partial degradation in the latex stage using a water-soluble degrading agent

Partial degradation of high ammonia natural rubber (HANR) in the latex stage was successfully carried out in the presence of periodic acid as a water-soluble degrading agent at ambient temperatures, i.e. 30 °C. The number average molecular weight (Mn), weight average of molecular weight (Mw), gel content and Mooney viscosity were decreased as the periodic acid concentrations increased. The polydispersity was slightly increased with increasing periodic acid concentrations. The relationship between Mw, gel content and Mooney viscosity was established. Mw in the range of 8.0 × 105 g/mol to 1.2 × 106 g/mol, and gel content between 30 and 45 wt% successfully achieved the Mooney viscosity of raw natural rubber ranging from 60 to 85 MU. To obtain such properties, periodic acid concentration between 17 and 19 phr was used to partially degrade the natural rubber in the latex stage. The structural characterisations determined by Fourier transform infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopies confirmed the occurrence of chain scission to form carbonyl terminal groups as a result of partial degradation. In summary, the Mooney viscosity of raw natural rubber can be controlled by partial degradation of natural rubber in the latex stage, contributed by a controlled decrease in molecular weight and gel content. Hence, this work may be useful in altering the properties of raw natural rubber that are suitable for processing of dry rubber products.

Tensile Strength of Protein-free Natural Rubber and its Vulcanizate Soaked in Water

Vulcanization, tensile strength and water-resistance of protein-free natural rubber (PFNR) were investigated in a viewpoint of application to a seal-product. The PFNR was prepared by incubation of high ammonia natural rubber (HANR) latex with urea, sodium dodecyl sulfate and acetone followed by washing with a centrifuge, twice. It was vulcanized with sulfur, zinc oxide, accelerator, stearic acid and anti-aging agent at 150 °C. Optimum vulcanization time and crosslink density were prolonged and lowered by removing proteins, respectively. The resulting vulcanized PFNR was characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) and nuclear magnetic resonance spectroscopy (NMR). After soaking in water, stress at break of vulcanized HANR decreased, whereas that of vulcanized PFNR did not. The PFNR in water was proved to be superior in the stress at break due to improvement of water-resistance that was a drawback of natural rubber.

The Occurrence of Phase Separation in Microcrystalline Cellulose Filled Natural Rubber Films

This paper describes the use of microcrystalline cellulose (MCC) as hydrophilic filler in two types of natural rubber latexes which are high ammonia natural rubber (HA) and epoxidised natural rubber latex (ENR). Light microscopy (LM), Scanning electron microscopy (SEM) and tensile strength measurements were then conducted on the resulting films. The light microscopy analysis revealed that more MCC particles appeared at the air–facing (AF) surfaces relative to the substrate-facing (SF) surfaces of the HA films with increasing MCC content. In contrary, the ENR25 films showed more or less similar MCC particles appearing at both air-facing surfaces and substrate-facing surfaces. Further SEM cryo-fracture analysis at the cross sections of the MCC filled ENR25 films indicated that the MCC particles were randomly dispersed in the rubber matrix. It can be suggested that the phase separation of MCC particles to the films surfaces occurred due to the incompatibility of MCC with the rubber matrix. Thus, it can be inferred that the occurrence of phase separation is minimised in the MCC filled ENR films in comparison to the MCC filled HA films.

Optimization study of ammonia and glutaraldehyde contents on vulcanization of natural rubber latex

This manuscript presents a continuation work on a simple system to vulcanize natural rubber using glutaraldehyde as a cross-linking agent. Natural rubber latex consists of protein which is allergenic to human body. The protein immobilization behavior of glutaraldehyde is of greatest interest to conduct this study. A study to determine the optimum condition for the vulcanization of the newly introduced system was carried out using glutaraldehyde as a cross-linking agent. Efforts were made to find out the best combination of glutaraldehyde and ammonia to vulcanize natural rubber latex with superior physical properties. Direct vulcanization method was employed to prepare natural rubber vulcanizates from natural rubber latex. The mechanical performance of the vulcanized natural rubber was determined for various combinations of ammonia and glutaraldehyde. Superior tensile properties were observed for the vulcanized rubber prepared from a very high ammonia natural rubber latex. The activation energy of the degradation of the vulcanizates was determined from thermogravimetric analysis. The cross-link density of the vulcanized rubber was determined from swelling experiments in toluene. The very high ammonia natural rubber latex (0.9 wt% ammonia) with 15 mL of 10 wt% glutaraldehyde solution was found to be the effective combination to vulcanize natural rubber latex with excellent properties. Advantage of this technique is the possibility of directly vulcanizing natural rubber latex at low temperature.

EFFECT OF DECELERATED FERMENTATION ON MORPHOLOGY AND MECHANICAL PROPERTIES OF NATURAL RUBBER LATEX

ABSTRACTDecelerated fermentation of natural rubber latex was performed to investigate the relationship between the morphology and mechanical properties of natural rubber. Natural rubber latex was preserved with sodium hydroxymethylglycinate, as a bactericide, to decelerate the fermentation of nonrubber components such as proteins, phospholipids, carbohydrate, and so forth. Gradual increases in the viscosity of the latex and gel content of the resulting rubber took place as the preservation period was prolonged, which were distinguished from less change in the viscosity of high-ammonia natural rubber (HANR) and high gel content of its rubber. The particle size distribution was dramatically changed during decelerated fermentation, although that of the HANR latex did not change. The pH and nitrogen content of the rubbers were independent of the preservation time. Morphology of the fermented natural rubber and the HANR was observed with scanning probe microscopy. Fewer mechanical properties of the fermented natural rubber were related to the destruction of the nanomatrix structure of the nonrubber components, which resulted from the decrease in the fatty acid ester groups with bacteria as compared with the good mechanical properties of the HANR.

Synthesis and characterization of water swellable natural rubber vulcanizates

Cassava starch-g-polyacrylamide superabsorbent polymer (SAP) was prepared by a reactive batch processing. Superabsorbent polymer composites (SAPCs) were prepared by blending the SAP with bentonite. Water swellable natural rubber (WSNR) was then prepared by blending high-ammonia natural rubber latex or dry blending of epoxidized natural rubber (ENR) or maleated natural rubber (MNR) with SAPC, poly(ethylene oxide) (PEO) and trimethylolpropane trimethacrylate (TMPTMA). WSNRs containing 10 phr PEO and 2 phr TMPTMA gave higher mechanical strength and water absorbency. Increasing the PEO loadings (20–40 phr) rendered higher absorbency with lower mechanical strength. A higher scorch time and cure time with a lower crosslinking density and cure rate index were found in the MNR-modified WSNRs compared with the unmodified WSNR or ENR-modified WSNR. ENR- and MNR-modified WSNR exhibited highest water absorbency with lower mechanical strength compared with the unmodified NR-based WSNR. The SAP and vulcanized rubber were thermally degraded under oxygen atmosphere, whereas 11% of the residues were bentonite and ZnO.

Quantitative analysis for reaction between epoxidized natural rubber and poly (L‐lactide) through 1H‐NMR spectroscopy

AbstractReaction between epoxidized natural rubber and poly(L‐lactide) (PLLA) was investigated quantitatively in terms of conversion of the epoxidized natural rubber. The epoxidized natural rubber was prepared by epoxidation of high ammonia natural rubber (HA‐NR) or deproteinized natural rubber (DPNR) with peracetic acid followed by depolymerization with ammonium persulfate. The resulting liquid HA‐NR having epoxy group (LENR) or liquid DPNR having epoxy group (LEDPNR) were subjected to heating at 473 K for 20 min, after blending with PLLA. The products were characterized through morphology observation, DSC measurement, and 1H‐NMR spectroscopy. The conversions of the rubbers were estimated from intensity ratio of signals in 1H‐NMR spectrum for the products after removing unreacted rubber with toluene. Difference in the estimated conversion between the LENR/PLLA and LEDPNR/PLLA blends was interpreted in relation to proteins present in the rubber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Structural characterization of vulcanized natural rubber by latex state 13C NMR spectroscopy

AbstractStructural characterization of vulcanized natural rubber was performed by high‐resolution latex‐state 13C NMR spectroscopy. The vulcanized natural rubber latex was prepared by vulcanization of high ammonia natural rubber latex with sulfur and sodium di‐n‐butyldithiocarbamate as vulcanizing agents. High resolution was attained for latex‐state 13C NMR spectroscopy even after vulcanization of the rubber latex, as is evident from no background in spectrum and narrow half width of signals, which were independent of vulcanization time. Small signals at 44 and 58 ppm in the carbon region were assigned by measurements of both distortionless enhancement by polarization transfer (DEPT) and attached proton test (APT) to secondary, tertiary, and quaternary carbons of crosslinking points. The assignment was proved by high‐resolution solution‐state NMR spectroscopy of vulcanized liquid cis‐1,4‐polyisoprene as a model, in which DEPT, APT, 2‐dimensional 1H‐13C correlation (HETCOR), and 2‐dimensional heteronuclear multiple bond correlation (HMBC) measurements were applied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1003–1009, 2007

Gel Formation in Natural Rubber Latex: 2. Effect of Magnesium Ion

Abstract The effect of Mg2+ ions on the gel formation in fresh and commercial high ammonia natural rubber latices (FL-latex and commercial HA-latex) was analyzed from the gel content and 2+ content after treatment with (NH4)2SO4. The gel content of rubber from commercial HA-latex decreased significantly after (NH4)2SO4 treatment comparable to that of FL-latex. Long-storage commercial HA-latex containing 50% gel fraction showed no decrease in 2+ content after (NH4)2SO4 treatment. This gel fraction was not solubilized in toluene by the treatment of a proteolytic enzyme in latex or ethanol/toluene mixed solvent extraction of rubber. The 2+ content of rubber in long-storage commercial HA-latex, 0.005% (w/w rubber), decreased after treatment with (NH4)2SO4, while the same treatment showed little change on FL-latex, 0.035%. The toluene soluble fraction of these latices showed a decrease in the Mn value with an increase in the (NH4)2SO4 concentration. The gel content of FL- and HA-lattices increased with an increasing storage period in the presence and absence of (NH4)2SO4. The initial rate of increase in the gel content was slow in the case of FL-latex. These findings indicate that the gel fraction in HA-latex is partly formed by ionic crosslinks caused by 2+ ions. Whereas, the gel phase in long-storage commercial HA-latex is presumed to be a hard gel predominantly formed by covalent bonding.

A Comparative Study of Styrene Polymerization in Deproteinized and Undeproteinized Natural Rubber Latex

Abstract An investigation on in situ polymerization of styrene in deproteinized natural rubber (DPNR) latex and high ammonia natural rubber (HANR) latex was carried out. The ratio of styrene to dry rubber was fixed at 25 : 75 by weight. It was observed that, at reaction temperature of 60 °C and reaction time of 10 hours, the styrene-DPNR system could attain a high conversion of 97% without adding surfactant. The degree of chemical bonding estimated for the resultant polystyrene-DPNR dried material was about 80%. The styrene-HANR system, however, required the addition of surfactant to complete the reaction time; but the conversion was found to be relatively low, in the region of 66%. This low conversion could be attributed to the role played by the protein/lipid layer, which is virtually absent in the styrene-DPNR system.

Surface Free Energy Analysis of Natural and Modified Natural Rubber Latex Films by Contact Angle Method

The contact angles of soft latex dipped films of high-ammonia natural rubber (HA) latex concentrate, deproteinized natural rubber (DPNR) latex, and oil-incorporated natural rubber latex were determined by the sessile drop method. The surface free energies were calculated using different procedures available in the literature. For each type of latex film, the harmonic-mean treatment gives the highest polar component of the surface free energy, while those from the Lifshifz−van der Waals acid−base method were the lowest. This trend is the same for each type of latex films but the magnitude varies. Among the various latex types, the unleached NR latex film surface is the most hydrophilic; the deproteinized latex film, the least. All the NR film surfaces were found to be monopolar basic in nature, with the unleached NR film being the most basic and those of HA the least. The behavior of the various film surfaces is discussed in terms of the presence of non-rubbers and their removal by washing (leaching) of the film or by deproteinisation of the latex. The polar nature of the film surface is correlated well with the presence of the exuded non-rubber materials at the film surface. The surface free energies of the latex films are comparable to that for synthetic cis-polyisoprene latex film but lower than that for chloroprene. These are in turn in reasonable agreement with the surface free energies of some common solid polymer surfaces. Discussion on the possible implications of the present results in the dipped-goods manufacturing process was attempted.

Novel Method for Preparation of Low Molecular Weight Natural Rubber Latex

Abstract Low molecular-weight natural rubber (LNR) and LNR latex was prepared by oxidative degradation of de-proteinized natural rubber (DPNR) latex in the presence of 1 phr of K2S2O8 and 15 phr of propanal, by shaking at 60 °C. The intrinsic viscosity [η] of DPNR with only K2S2O8 decreased from 7.2 to 5.5 after 2 h and then increased to 6.5 after 3 h. By the addition of propanal, DPNR showed a significant decrease in the [η] value of LNR with [η] of about 0.5 after 5 h of the reaction, while rubber from high-ammonia natural rubber (HANR) latex showed a slight decrease in [η]. The concentration of latex and the kind of surfactant used for stabilizing the latex had little effect on the degradation rate of DPNR latex. The LNR latex is stable as the latex form and the dried rubber coagulated from latex is transparent and colorless. The LNR was a telechelic polymer containing aldehyde and ketone groups at both terminals as determined by NMR and molecular weight analyses.