Highly impact toughened and excellent flame-retardant polylactide/poly(butylene adipate-co-terephthalate) blend foams with phosphorus-containing and food waste-derived flame retardants

Green polymeric foams are an important research topic for sustainable development. In this study, a natural multifunctional flame-retardant additive based on food waste was developed and evaluated for its ability to replace the commercial additives tricresyl phosphate (TCP) and trioctyl phosphate (TOP) in a polylactide/poly(butylene adipate-co-terephthalate) (PLA/PBAT) foam. A series of blend foams with additives were prepared by melt extrusion. According to the results, the blend foam with 20 phr of TCP showed the best combination of impact toughness and flame retardancy. TCP, however, poses health and environmental risks. Therefore, natural flame retardants (NFRs) were used to partially replace the commercial flame retardant (CFR). A combination of TCP and soybean residue (SB) produced an impact toughened and flame-retardant blend foam. When compared to the neat PLA/PBAT foam, the impact toughness of the best sample was increased by about 256 %. The optimal foam showed excellent flame resistance with a V-0 UL-94 rating and a high LOI value (31.8 %). SB has the potential to partially replace TCP as flame retardant and could be used in a broad range of PLA/PBAT foam applications.

Poly(lactic acid) foams reinforced with cellulose micro and nanofibers and foamed by chemical blowing agents

Biodegradable polymeric foams have gained increasing attention as an alternative to conventional polymeric foams, whose recycling is economically unviable due to its low density. Based on this, this article discusses the development of poly(lactic acid) foams produced with the insertion of four and eight parts hundred resin (phr) of long and short cellulose fibers and nanofibers. Short fibers of nanocellulose were obtained by mechanical defibrillation and dried by lyophilization, and long fibers by CO2 supercritical fluid extraction. The poly(lactic acid) foams were produced by adding a chemical blowing agent with a pressure-free expansion method. In general, short fibers of cellulose act as nucleating agents during the expansion of the foam, which is observed by its greater number of smaller-size cells than the non-reinforced poly(lactic acid) foams. The insertion of long fibers of cellulose restricts the mobility of the polymer matrix during the expansion, thus hindering the foam its growth and formation of bubbles.

Foam extrusion of PP-based wood plastic composites with chemical blowing agents and the Celuka technique

Wood plastic composites have gained relevance in recent years as an alternative to wood boards. However, because the cavities in wood fibres are compressed by high processing pressure during the extrusion of wood plastic composites, the product densities show a range of up to 1.5 g/cm3 depending on wood content and base material. Particularly in large-sized products, this may be disadvantageous for processors and end users. Foaming of the plastic matrix is a promising approach to reduce the density of wood plastic composites products. This article discusses the foam extrusion of PP-based wood plastic composites with chemical blowing agents in combination with the Celuka technique. Integral wood plastic composites foam with a rigid and plain outer layer was produced using a parallel, counter rotating twin screw extruder. The profiles obtained were analysed with respect to foam structure and mechanical properties. It was possible to achieve a density reduction of up to 0.7 g/cm3 in the foamed wood plastic composites profiles. Furthermore, we demonstrate that wood fibre length and type of chemical blowing agent have a strong effect on the resulting foam morphology.

Foaming behavior of cellulose fiber-reinforced polypropylene composites in extrusion

This paper investigates the effect of polypropylene type and cellulose content on the foaming behavior of cellulose fiber-reinforced polypropylene composites in extrusion. Two types of polypropylene (linear and branched structures) were used as a polymer matrix. The thermal properties of the composites were characterized by a differential scanning calorimeter, and the viscosity of the composites was evaluated by a rotational rheometer. The foaming behavior of the composites was examined using an extrusion foaming system, in which carbon dioxide was used as a physical blowing agent for foams. The results suggested that the cell density increased with the increase of cellulose content. On the other hand, the void fraction decreased with the addition of cellulose, but the void fraction at the 40 wt% cellulose was higher than that at the 20 wt% cellulose. The results also indicated that the two types of polypropylene had a minimal effect on the foaming behaviors of the cellulose fiber composites.

Strategies for Processing Wood Plastic Composites with Chemical Blowing Agents

The production of a cellular structure in wood-flour/plastic composites (WPC) is overwhelmingly dominated by the gaseous emissions/ volatiles released by the wood-flour (WF), which prevents the formation of a uniform and fine-celled structure. By adopting effective processing strategies, the adverse effects of these volatile emissions on the foam morphology of WPC can be largely suppressed. This study discusses these strategies, and presents the results obtained from extrusion processing in cases where the chemical blowing agent (CBA) predominantly controls the density reduction. The effects of CBAs on extrusion processing of WPC are discussed. All the CBAs used, produced uniform and reasonably fine-celled structures.