Modification Of Natural Rubber Research Articles

Effect of Monomers in the Structural Modification of Natural Rubber During Grafting with γ‐Ray Irradiation

Nonirradiated latex (NIL), irradiated latex (IL) and the latex grafted separately with monomers such as styrene, butyl methacrylate (BMA), methyl methacrylate (MMA), and cyclohexyl methacrylate (CHMA) were prepared from natural rubber obtained by Bangladesh Forest Industries Development Corporation, Bangladesh. Morphology and mechanical properties of the six different rubber films were observed by mechanical testing, optical microscopy, and x‐ray diffraction methods. An inhomogeneous electron density is developed as a consequence of cross‐linking and grafting during irradiation. The resultant structure includes density fluctuation of several nanometers to microns as revealed by small‐angle x‐ray scattering (SAXS) and microscopy. The rubber elasticity is enhanced due to the network structure, resulting in high tensile strength and high elongation in the IL. Aggregation of the grafted latex increases tensile strength and decreases elongation. Consequently, the greater the population of aggregates in the grafted film, the lower the elongation values. The mechanical properties and corresponding structures are explained by a polymer gel theory using a spring model. Considering numbers of junction N and the average length of the spring L with the spring constant k, the tensile strength (T) is proportional to NkL max. As the elongation at break (E) depends on L max (the maximum length of L), the relative value of N can be estimated from the mechanical results by (T/E)3/5. The experimental results are well explained by the gel theory. Existence of large‐sized aggregates by grafting and homopolymerization increases stiffness and brittleness of the rubber material.

Modification of natural rubber with phosphatic plasticizers: a comparison of phosphorylated cashew nut shell liquid prepolymer with 2-ethyl hexyl diphenyl phosphate

The vulcanization characteristics, tensile properties, thermal decomposition characteristics and flame retardancy of Natural Rubber (NR) modified with phosphorylated cashew nut shell liquid (PCNSL) prepolymer has been studied and compared with 2-ethyl hexyl diphenyl phosphate (Santicizer-141), at concentrations ranging from 10 to 20 phr. The PCNSL modified NR vulcanizates showed higher tensile properties and resistances to thermo-oxidative decomposition and flame compared to that containing similar dosages of Santicizer. Kinetic parameters for themo-oxidative decomposition, obtained from dynamic thermogravimetry, indicated a higher degree of condensed phase reactions for the PCNSL modified NR vulcanizates, especially at higher heating rates and in presence of higher concentrations of PCNSL.

Modification of natural rubber: a study to assess the effect of vinyl acetate on the efficiency of grafting methyl methacrylate on rubber in latex form, in the presence of azo-bis-isobutyronitrile

On the basis of the proposal that highly reactive vinyl acetate (VAc) radicals could facilitate the grafting of other monomers on to natural rubber (NR), the effect of the presence of small quantities of VAc on the efficiency of grafting methyl methacrylate (MMA) on NR molecules in latex form has been studied. Several VAc concentrations have been examined, and the initiator azo-bis-isobutyronitrile was added to the systems to promote the formation of VAc radicals. There is good evidence for the formation of graft copolymer under the conditions used, but it was found that the grafting is not significantly affected by the presence of VAc. It is proposed that this could be due to the fact that the oil-soluble initiator is not accessible to the relatively large amount of VAc present in the aqueous phase. A higher than expected portion of the products was extractable with petroleum ether, and this may be attributable to the initiator inducing a small amount of degradation in the rubber. Finally, although acetone is not considered a good solvent for NR, it was found to be capable of extracting from the graft copolymers relatively large quantities of material containing the cis-1,4-polyisoprene structure. This observation is consistent with the effect that PMMA grafts on the NR molecules would have on their solubility in this solvent.

Modification of natural rubber with a macroannular polymer

Modification of natural rubber with a macroannular polymer

Modification of natural rubber by different grafting techniques

An attempt has been made to graft a hydrophylic monomer of N,N.dimethyl acrylamide (DMAA) onto natural rubber (NR) tube by simultaneous, per-oxidation and preirradiation grafting techniques. It was found that the grafting by simultaneous grafting technique results a maximum 29 wt% degree of grafting and by peroxidation and preirradiation techniques, results the maximum 42 wt% and 13 wt% degree of grafting, respectively. It was concluded that the peroxidation technique is the most appropriate to obtain a high degree of grafting in radiation copolymerization of DMAA onto NR.