Recycling printed polypropylene labels and polyolefins caps as chemical foaming agent to produce foam products

Recycling printed polypropylene (PP) labels and printed polyolefins (PO) caps as a chemical foaming agent to produce foam products is studied. An experimental Taguchi L16 design with seven experimental variables involved is used: talc content and screw angular velocity, at four experimental levels; extrusion temperature profile and extruded formulations, at three levels; and, type of label washing process, the use of metal mesh and the type of label drying process, at two levels. As control variables, the morphology of the cells and the density of the foamed products are utilized. The labels/caps mixture was composed of 21% printed PP labels and 79% printed polyolefin caps. Part of the pigments from the ink labels and some polar groups of low-molecular-weight materials present in the molten polymer were partially decomposed at the PP processing temperatures, which contributes to the cell formation and growth of the extruded foams. The labels/caps mixture generated large ellipsoidal and elongated cells (740 µm) oriented in the extrusion direction because of the presence of high density polyethylene (HDPE) and EVA in the recycled PP caps and labels. The experimental factors that influenced the foam density were the screw angular velocity and temperature, and the cell morphology depended on the matrix crystallinity and melt strength.

Thermally insulating extruded foams laminated with barrier films

Extruded styrenic foam can provide considerable insulation performance, making it a suitable material for a wide variety of building applications. Its thermal resistance over time is heavily influenced by the diffusion rate of oxygen and nitrogen from the ambient air environment into the cellular structure, and which, if moderated, can lead to still more effective systems. Application of a barrier to surfaces of the foam as a means to provide more controllable gas exchange can be accomplished through use of multilayer ethylene vinyl alcohol-based polymeric films designed specifically for the purpose. Behavior of barrier-faced foam systems with respect to cell gas content, mechanical properties, thermal insulation performance over time, and barrier integrity is described, along with potential benefits of its use in practice.

Improved compression properties of polypropylene extrusion foams by supramolecular additives

Owing to the high lightweight design potential polymer foams become increasingly important. For rigid polymer foams, requiring high dimensional stability under load, a high compression modulus is a key feature. Here, we demonstrate how supramolecular additives can be utilized to control the foam morphology and to significantly improve the compression behavior of extruded foams made of linear isotactic polypropylene. Three different 1,3,5-benzenetrisamides were selected as supramolecular additives. These additives are soluble in the polymer melt and form a supramolecular nanofiber network upon cooling, acting as nucleating sites for both, foam cells and polymer crystals. It is shown that the in situ formed nanofiber network is very effective in reducing the cell size of extruded foams. Depending on the molecular structure and the concentration of the supramolecular additives, the compression modulus of polypropylene-polymer foams can be significantly increased compared to a reference foam with talc. Unexpectedly, an improvement of 100% with a concentration of only 0.02 wt% of a supramolecular additive compared to the neat polypropylene foam featuring similar densities is achieved. This improvement cannot be correlated with the foam morphology and is most likely attributed to the presence of the supramolecular nanofiber network.