Spatiotemporal emergence of lamellar branching morphology of polymer spherulite has been investigated theoretically in the framework of a phase field model by coupling a crystal solidification potential pertaining to a nonconserved crystal order parameter with a temperature field generated by latent heat of crystallization. A local free-energy density having an asymmetric double well has been utilized to account for a first-order phase transition such as crystallization. To account for the polymorphous nature of polymer crystallization, the phase field order parameter of crystal at the solidification potential of the double-well local free-energy density is modified to be supercooling dependent. The heat conduction equation, incorporating liberation of latent heat along the nonuniform solid-liquid interface, has led to directional growth of various hierarchical structures including lamella, sheaflike structure, and spherulite. Two-dimensional calculations have been carried out based on experimentally accessible material parameters and experimental conditions for the growth of syndiotactic polypropylene spherulite. The simulations illustrate that, under self-generated thermal field, the initial nucleus is anisotropic having lamellar stacks that transforms to a sheaflike structure and eventually to a lamellar branching morphology with a dual-eye-pocket texture at the core. It appears that the released latent heat is responsible for the lamellar side branching and splaying from the main lamellae. On the same token, the heat build-up seemingly prevents the interface boundaries of neighboring spherulites from over running on each other during impingement, thereby forming the grain boundary.

The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation captures ripple formation running across the long lamellar growth front, which may be attributed to lamellar buckling caused by the volume shrinkage. Of particular interest is that these simulated topologies of the single crystals are in good accord with the growth character of syndiotactic polypropylene single crystals observed experimentally by us during isothermal crystallization from the melt.

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Study the effect of kaolin clay as a synergistic agent on flame retardancy and thermal degradation in natural rubber based on intumescent flame retardant (IFR); consisting of ammonium polyphosphate (APP) as acid source, pentaerythritol (PER) as a carbonization agent and melamine (ME) as a blowing agent was undertaken. The intumescent was examined at different loading (60, 80 and 100 phr). Kaolin clay was incorporated into flame retardant at four different concentrations (0.5, 1.0, 1.5 and 2.0 wt% of flame retardant) to investigate the synergism between the flame retardant materials. The flammability and thermal degradation of composites were characterized by UL-94 rating (vertical burning) test, cone calorimeter (CONE) and thermogravimetric analysis (TGA). All composites could meet the UL94V-0 standard. A synergist effect was observed when kaolin clay is used in combination with the intumescent flame-retardant through the TGA and CONE results. Moreover Scanning Electron Microscope (SEM) was done for the char morphology.

Silica has been used as reinforcing filler in natural rubber for a period of time as it results in excellent properties for NR vulcanizes. Rice husk ash (RHA), bagasse ash (BA), and oil palm ash (OPA) obtained from agricultural wastes are mainly composed of silica in the percentage of 80.00%, 57.33%, and 40.20% by weight, respectively. The effect of these fillers on cure characteristics and mechanical properties of natural rubber materials at fixed silica content at 35 parts per hundred of rubber (phr) were investigated. The results indicated that ashes showed greater cure time compared to that of the silica. The incorporation of ashes into natural rubber gradually improved compression set but significantly decreased tensile strength, elongation at break, and resilience. Moreover, young's modulus increased, while hardness showed no significant change with the addition of ashes. Overall results indicated that ashes could be used as cheaper fillers for natural rubber materials where improved mechanical properties were not critical.