Improving the stability of polylactic acid foams by interfacially adsorbed particles

Abstract

Polymers such as poly(lactic acid) (PLA), which have poor melt strength, are difficult to foam due to severe cell coalescence during foaming. We show that addition of a few percent of polytetrafluoroethylene (PTFE) particles can stabilize PLA foams against bubble coalescence and collapse. The particles and a chemical blowing agent, were dispersed into the PLA by extrusion, and then foamed by heating. The PTFE‐containing foams remained stable even when the foams were held under molten conditions for extended periods. Foam stability is attributed to an interfacial mechanism: due to their low surface energy, the PTFE particles adsorb on the inner surface of the foam bubbles at a high surface coverage, and endow the bubbles with an interfacial “shell” that prevents coalescence. This mechanism resembles the particle‐stabilization of Pickering emulsions in oil/water systems. Particle adsorption at the interface is a necessary condition for using this approach, and hence this approach is most likely to be successful if the particles have a low surface energy and the polymer has a high surface tension. The approach of using interfacially adsorbed particles can be broadly generalized, and offers the opportunity of foaming various polymers with low melt strength, or for expanding the processing window within which foaming can be conducted. POLYM. ENG. SCI., 56:9–17, 2016. © 2015 Society of Plastics Engineers

Development and Characterization of Functional Polylactic Acid/Chitosan Porous Scaffolds for Bone Tissue Engineering

“…There are several methods to fabricate porous biodegradable synthetic polymer scaffolds, such as particulate-leaching [ 28 , 29 ], emulsion freeze-drying and phase separation [ 30 ], gas foaming [ 31 , 32 ], and even 3-D printing [ 33 ]. However, to promote cell adhesion and proliferation, most of the previous work presented in the literature needs a further solvent treatment to add biocompatible materials inside the scaffolds’ pores, such as CS, leading to unwanted residual solvents deeply trapped inside the scaffolds’ matrices [ 34 , 35 ].…”

Effect of Biomass as Nucleating Agents on Crystallization Behavior of Polylactic Acid

“…Examples of reported biomass nucleating agents include: lignocellulosic materials (hemicellulose, lignin and cellulose) in plant cell walls [ 26 , 27 , 28 ]; natural fiber and wood powder from wood [ 29 , 30 ]; chitin and chitosan in the protective epidermis of crustaceans and the cell walls of some fungi [ 31 , 32 , 33 ]; and starch and its natural product, cyclodextrin [ 34 , 35 ]. The addition of these biomass materials to PLA was found not only to maintain the original biodegradability of PLA but also to improve its crystallization performance.…”

Improving the processibility and mechanical properties of poly(lactic acid)/linear low‐density polyethylene/paraffin wax blends by subcritical gas‐assisted processing

“…To overcome this, PLA has been modified in several ways to increase its processability, mechanical properties, and crystallization kinetics for improved thermal stability . Such modifications include blending it with other fillers and polymers such as organic montmorillonite (nanoclay) , graphite , bamboo fibers , talc , natural rubber , polytetrafluoroethylene (PTFE) , polystyrene (PS) , polypropylene (PP) , poly(ɛ‐caprolactone) (PCL) , poly(ethylene glycol) (PEG) , thermoplastic polyurethane (TPU) and introducing foaming agent . Previous studies have shown that paraffin wax (PW) is capable of improving the ductility and fluidity of PLA matrices .…”