Evaluation of the applicability of natural polymers as coupling agents in imparting reinforcement action of silica fillers in NR latex films

Abstract

The results of an evaluation of the applicability of natural polymers (NPs) as coupling agents in imparting reinforcement action of silica fillers in natural rubber (NR) latex films are described in this research investigation. Three types of NPs namely; chitin, chitosan and cellulose were used for this investigation. Standard extraction processes were used for the extraction of chitin and chitosan. A commercially available grade of cellulose was used for this investigation without purification. Modification of surface of silica particles with NPs was affected by two techniques; in-situ surface modification, and surface modification through a sol-gel process. Coupling action of these NPs was compared with that of the most widely used commercially available coupling agent silane, Si69. A range of stable aqueous colloidal dispersions of precipitated silica were prepared with the use of NPs and Si69. In-situ surface modification performed with NPs and Si69. With NPs, the surface modification was done at four different proportions as 2.5%, 5%, 7.5% and 10% by weight of silica. With Si69, the modification was done at two different proportions as 5% and 10% by weight of silica. Sol-gel surface modification performed with chitosan was done at two different proportions as 5% and 10% by weight of silica. Interactions between polar groups of silica and functional groups of the NP which hinder aggregation of silica particles were confirmed by FTIR spectroscopy. The dispersion stability of the unmodified/modified filler (UMF/MF) dispersions was assessed by observing the phase separation upon standing. Dispersion stability of MF dispersions prepared using both surface modification method is much better than that of UMF dispersions. The particle size distribution of unmodified/ modified filler dispersions was measured by using “Fritsch” particle size analyzer. The particle size of the modified filler with cellulose was found to be lower than that of UMF dispersion. Effectiveness of NPs in enhancing reinforcing action of silica in NR latex was evaluated through investigation of mechanical properties of vulcanized films cast from NR latex compounds containing modified/unmodified fillers in different proportions. Distribution of unmodified/modified fillers within the rubber matrix was investigated through metallurgical microscope and scanning electron microscope by examining micrographs of surfaces of dipped NR latex films and micrographs of cross sections of cast NR latex films containing modified/unmodified fillers respectively. High colloidal stability of modified fillers with NPs indicates that are capable of acting as colloidal stabilizers for silica dispersions. Some of the NPs tested were found to be capable of conferring an appreciable enhancement in reinforcing action of silica in NR latex films. Micrographs graphs of the filled NR latex films revealed that same NPs have conferred uniform distribution of filler particles within the rubber matrix.