Morphology and aggregation process of natural rubber particles

Natural rubber particles (NRPs) are the main place of natural rubber biosynthesis and storage which exist as the organelle in the latex tube cells of rubber trees. Here, we observed the aggregation process from the morphology of rubber particles and correlated the aggregate structure with the mechanical properties. The rubber particle sizes were first examined by optical microscopy, and the distribution showed a Gaussian curve with an average diameter of 1200 nm. Scanning electron microscopy (SEM) was then used to photograph the smaller particles, which supported a Gaussian distribution for NRPs smaller than 200 nm in diameter. They collectively indicated a bimodal distribution of NRP size, consistent with the results of the laser particle size analyzer. The percentage of the small rubber particles was measured to be 68.3 % and 31.7 % for the large rubber particles. The aggregation process of NRPs was observed as membrane fusion, superimposed aggregation, followed by the concavity of the inner core from the outside, and finally the formation of aggregated state rubber. Subsequently, the natural rubber latex films were obtained by spreading the latex at room temperature. The green strength was tested in its naturally dried stacked aggregated state, reaching a notable strength of 8 MPa. This was about 7 times higher than that of the ribbed smoked sheet (RSS). In contrast, when the naturally dried rubber film was processed by high-temperature molding and low-temperature setting, its green strength dropped to the level of the RSS. It thus supports that the processing methods, such as high temperature and shearing, could significantly impact the structure and performance of natural rubber (NR). Consequently, excellent performance of elastomeric materials might be reached under low-temperature drying and normal-temperature vulcanization processing methods.