Morphology and Mechanical Performance of Polystyrene/Polyethylene Composites Prepared in Supercritical Carbon Dioxide

Abstract

Polystyrene/polyethylene composites have been prepared by the heterogeneous radical polymerization of styrene within supercritical carbon dioxide−swollen high density polyethylene (HDPE) substrates. Composition of the composites can be controlled with reaction time and initial ratio of styrene to HDPE. The polystyrene produced within the substrate is of high molecular weight. Differential scanning calorimetry and wide-angle X-ray diffraction indicate that the crystalline portion of the HDPE substrate is unaffected by the procedure used in this investigation. Scanning electron microscopy indicates that the polystyrene resides in the noncrystalline domains and permeates throughout the spherulitic structure of the HDPE substrates. This morphology is very different from the morphology of polystyrene/polyethylene blends produced by conventional melt/mixing techniques. The strengthening of the spherulitic structure of HDPE produces an efficient enhancement in the modulus of the overall composite. The tensile strengths of the composites are dramatically enhanced over conventionally produced blends. The addition of brittle polystyrene to extremely tough HDPE substrates decreases the overall fracture toughnesses of the composites.

Thermodynamics and Kinetic Processes of Polymer Blends and Block Copolymers in the Presence of Pressurized Carbon Dioxide

“…This aspect is particularly important for blends where one or more component degrades or reacts to generate by-products at elevated temperatures. CO 2 -assisted impregnation and polymerization yields improved functionality relative to the homopolymer substrate and better performance as compared to conventional meltprepared polymer blends (e.g., higher modulus, [202][203][204][205] higher tensile strength, [202][203][204]206] improved impact strength, [205][206][207] increased conductivity, [208,209] and enhanced thermal stability). [209] This method also provides an avenue to blends of hydrophobic polymers (e.g., PVC or PMMA) with water-soluble polymers (such as poly(methacrylic acid) (PMAA)) that are not easily accessible by conventional means.…”

“…[203,207,[211][212][213] A decisive consideration here is that the blend composition is not limited by the solubility of the monomer in the fluid or matrix phase, since polymerization depletes the monomer reservoir and permits more than the equilibrium concentration of the monomer to penetrate into the polymer substrate. [201,202,207,214,215] The resulting blends can be further modified through additional chemical means such as chemical crosslinking and surface sulfonation; [201] alternatively, the polymerization can be restricted to the substrate surface, thereby yielding a grafted surface layer. [212,216] This approach has also been implemented [212,216,217] to graft secondary species onto existing polymers.…”

“…In one case, it has been observed that grafting poly(acrylic acid) (PAA) to iPP does not lead to any discernible changes in T m and the crystallinity of the iPP substrate (since the grafting reaction is limited to amorphous iPP regions). [212] Although the crystal structure of the substrate polymer remains largely unaffected by the incorporation of grafted chains, [202,211] accompanying reductions in T m have been reported. [216] Morphological analysis [202] of CO 2 -impregnated polymer blends reveal that polymerized PS resides in amorphous regions of HDPE, as well as throughout existing spherulites (Fig.…”

“…[212] Although the crystal structure of the substrate polymer remains largely unaffected by the incorporation of grafted chains, [202,211] accompanying reductions in T m have been reported. [216] Morphological analysis [202] of CO 2 -impregnated polymer blends reveal that polymerized PS resides in amorphous regions of HDPE, as well as throughout existing spherulites (Fig. 15), which constitutes a level of mixing not previously achieved by conventional blending of these two polymers.…”

In situ polymerization and nano‐templating phenomenon in nylon fiber/PMMA composite laminates

“…9 In addition, a significant amount of work has emerged elucidating the use of SC CO 2 as a unique solvent for polymer chemistry. 10 McCarthy et al 11 have shown that monomer can be diffused into the amorphous regions of swollen host polymer and polymerized in situ. By this process they have made some very interesting kinetically trapped polymer blends.…”