ABSTRACT:The chemical mode of action as a flame retardant of calcium carbonate nanoparticles combined with ammonium polyphosphate in polypropylene was investigated. Reduction in burning rates for 0.5 mm thick samples were observed without appreciable char formation up to 30 wt % loading of additives. Thermogravimetric analysis (TGA) of the mixture of CaCO 3 and ammonium polyphosphate (APP) showed that calcium carbonate nanoparticles react with ammonium polyphosphate before the degradation of the phosphate chains. TGA-FTIR studies of the polymer composite samples and powder mixtures of the additives confirmed the evolution of ammonia and carbon dioxide due to interaction between the additives. X-ray diffraction (XRD) analysis of chars, obtained after burning the films, showed definite diffraction peaks corresponding to that of calcium metaphosphate. The inert gasses produced by the interaction of the additives hindered the advancing flame and, thus, reduces the burning rates, at times even without char formation.

ABSTRACT:We investigated the effect of organically modified clay alone and in combination with zinc borate on the thermal/flammability behavior of nylon-6 nanocomposites. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increase in clay concentration. Nanocomposite films of approximately 0.5 mm thickness with 2.5 and 5 wt % clay burned for almost the same duration as neat nylon-6 but with reduced dripping in horizontal flame test. The 10 wt % clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25-30%. Zinc borate/clay containing nanocomposite developed into a very good intumescent system in cone calorimeter test, swelling about 10-13 mm height prior to ignition forming a cellular char structure. This was found to be an effective composition in reducing the heat release and mass loss rate of nylon-6 by about 65% and at par with 10 wt % clay nanocomposite. Flame retardant behavior could be attributed to distinct char morphologies observed through scanning electron microscopy. Fourier transform infrared spectroscopy of the 10 wt % clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char.

Polymer blending is a versatile method for production of co-continuous porous materials. While numerous studies have been performed to elucidate the thermal annealing effects on the bulk structure, the effect of geometrical confinement is little understood. In the present work, possible effects from geometrical confinement during in-mold annealing were explored. A 50/50 wt.% poly (lactic acid)/polystyrene (PLA/PS) blend was compression molded and annealed between two parallel plates without being confined circumferentially during the compression molding process. Different conditions for geometrical confinement, including varied gap size and compression ratio (initial to final thickness ratio), as well as modified surface properties, were employed. The experimental results indicated that the gap size played a profound role in affecting the structural development; the phase size near the mold surface was smaller than away from the surface. The actual phase structure and the resulting gradient in pore size were further affected by the mold surface properties. Additionally, the compression ratio was found to affect the morphological development especially near the mold surface. At a high compression ratio, a thin layer of PLA was formed immediately during compression. The thickness of this layer either grew or reduced in size depending on the mold surface properties. Understanding of these geometrical confining effects and implementing them in processing may lead to the development of innovative porous materials.

Flame‐retardant properties of nylon 6/organically modified montmorillonite (OMMT) thin films, fibers, and fabrics were investigated to determine the efficacy of condensed‐phase flame‐retardant mechanism in relation to montmorillonite concentration, sample geometry, and flame test conditions. Horizontal flame spread conducted on thin films revealed no significant difference in burning behavior between nylon 6 and nanocomposites with 5 wt% OMMT. However, with a higher concentration level of 8–10 wt% OMMT, the films burned without any dripping. The flame spread rate was reduced by 30–40% as compared with nylon 6 films. Cone calorimeter study on nanocomposite films showed that the peak heat release rate of nylon 6 was reduced by 65–67% with 8–10 wt% OMMT. Undrawn nanocomposite monofilaments with 10 wt% OMMT burned slowly and steadily in Bunsen flame without dripping. In cone calorimeter, nanocomposite fabrics with 8 wt% OMMT showed reduced heat release rate and mass loss rate compared to nylon 6 fabrics with increase in fabric tightness factor. The mass loss rate was about 40–60% less when compared with nylon 6 fabrics. The fabric char structure remained intact after burning. This demonstrated the interdependence of fabric tightness factor, OMMT concentration, and source of heat flux in forming a protective char and affecting the flammability of fabrics. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Processing‐related properties of a polypropylene (PP)/silicone oil blend were investigated. It was found that an addition of a small amount (∼2 wt%) of silicone oil, a low molecular weight linear poly(dimethyl siloxane) (PDMS), drastically changed the rheological properties of PP. The PDMS seemed to work both as an internal lubricant and an external lubricant in the blend system. In particular, the apparent viscosity of the blend in capillary rheometry was approximately 10 times lower than that of virgin PP. The local minima in the viscosity versus shear rate curve in capillary rheometry and the gap‐dependency of viscosity in parallel‐plate rheometry implied the existence of a slip wall condition, caused by the formation of a thin lubricant layer at die walls. Thermal analyses and mechanical tests showed that the thermal and mechanical properties of the blend were nearly unaffected by the minor addition of silicone oil. The blend was tested in a profile extrusion process, and a significant reduction in die swell and profile distortion was achieved. The jet stretchability or spinnability in fiber spinning was also greatly improved with the minor addition of silicone oil. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers