Studies on the thermal characteristics of polymer alloys

Abstract

PVC: polystyrene alloys of varying compositions were prepared by the film casting technique. Thermogravimetric analysis of these materials showed that the decomposition patterns of the alloys are quite different from those of the constituent polymers. These results are explained in terms of polymer interaction phenomena.The blending of two or more polymers to form novel materials is an operation that usually reduces composition non-uniformity [1]. This has important technological implications, as chemical, physical and mechanical properties, as well as appearance, all depend upon composition uniformity. In fact, it is known [2-4] that these alloys very often exhibit a synergism in properties achievable only through this technique. Blending methods usually [5] involve solid -to -liquid, solid -to -solid or liquid -to -liquid mixing.The two polymers chosen for this investigation have extensive industrial and household applications. In a recent article [6], we showed by means of DSC that PVC and polystyrene (PSt) are a compatible macromolecular pair (single Tg when blended). The present paper reports the results of TG studies on this blend. Experimental MaterialsThe PVC and PSt samples were supplied by Aldrich Ltd., and have intrinsic viscosities of 0.75 and 0.86, respectively. Analytical grade tetrahydrofuran (TFH) solvent was procuced from BDH.

Effect of Density on Flame Characteristics of Some Tropical Timbers

“…The timber species that had the highest flame duration values were mostly of medium density except for Khaya senegalensis which is quite dense. This shows that though the effect of density cannot be overlooked in determining the fire characteristics of timber, other factors such cellular structure, molecular composition and timber extractives deserve special attention in exp laining these results [White, 2000;Eboatu & Altine, 1991;Babrauskas, 2001]. Also the effect of density on FPR (Figure 8) proposes that as the porosity index of the timber species decreased with increase in density, the rate of flame spread was reduced accordingly.…”

“…Each of the timber species was cut into cubes and splints. Dry and wet densities, moisture content, ignition time, flame duration, flame propagating rate and after-glow time were determined as described elsewhere [Momoh et al, 1996;Eboatu & Altine, 1991;Eboatu et al, 1995]. Each experiment was repeated five times and the results averaged.…”

“…Fire has been and is still a major environmental factor, contributing to global warming and destroying the rich forest resources of the world. Little has been reported on the flammability properties of most tropical timbers [Eboatu & Altine, 1991;Momoh et al, 1996;Eboatu et al, 1997].…”

Correlations of Major Flame Characteristics of Some Fire Tolerant Trees in South-East Nigeria by Coefficient of Determination (R2)

“…Even in the case of timbers having similar densities, the afterglow times are substantially different. It is likely that apart from the density of the timber, the nature of the unburned material that has gone through thermal episode, in form of char (whether dense or open), the depth to which the surface flame had sunk as it traversed the wood surface, may help to explain the result [36]. The moisture content of the timbers ranged between 8.02 and 11.56% as presented in Table 1.…”

Evaluating the Compatibilities of Some Polymer Pairs, by Viscometry

“…Thus, establishing points and compositions of maximum interaction is necessary for blend formation instead of blindly mixing polymer pairs. Mixing of two or more polymers to produce blends is aimed at achieving desirable properties, without the need to synthesize special novel polymer systems [6][7]. In other words, the reason for blending, is to find two or more polymers whose mixture will have synergistic property improvement beyond those that are purely additive in effect.…”