Bio-based poly(lactic acid) foams with enhanced mechanical and heat-resistant properties obtained by facilitating stereocomplex crystallization with addition of D-sorbitol.

The preparation of bio-based poly(lactic acid) (PLA) foams with high mechanical properties and heat resistance is of great significance for environmental protection and green sustainable development. In this paper, D-sorbitol (DS) containing six hydroxyl groups was introduced into poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) blends for first time to promote the formation of stereocomplex (SC) crystals, which could improve the foaming behavior and enhance mechanical properties and heat resistance of PLA foams. The results showed that DS could improve the formation efficiency and crystallinity of SC crystals by enhancing the hydrogen bonding between the enantiomeric molecular chains. Furthermore, the compression modulus and interactions Vicat softening temperature of the PLLA/PDLA/DS blend foam increased about 854% and 16% compared to the pure PLLA foam, respectively. Besides, when the annealing process was introduced, the compression and heat resistance of the PLA foams increased further. This study provided a feasible strategy for the preparation of bio-based and biodegradable PLA foams with outstanding compressive and heat resistance properties.

Green and effective fabrication of porous surfaces with adjustable cell structure by foaming at incomplete healed polymer-polymer interface.

Porous surfaces of materials have shown huge potentialities for endowing materials with multifarious functions. Despite introducing gas-confined-barriers in supercritical CO2 foaming technology is effective to weaken the gas escape effect and facilitate the preparation of porous surfaces, the differences in intrinsic properties between barriers and polymers result in bottlenecks like cell structure adjustment limitation and incompletely eliminated solid skin layers. This study undertakes a preparation approach for porous surfaces by foaming at incompletely healed polystyrene/polystyrene interfaces. In contrast with employing gas-confined-barriers reported before, the porous surfaces foamed at incompletely healed polymer/polymer interfaces show a monolayer, full-open cell morphology, and wide adjustable range in cell structures including cell size (120 nm∼15.68 µm), cell density (3.40 × 105 cells/cm2∼3.47 × 109 cells/cm2), and surface roughness (0.50 µm∼7.22 µm). Furthermore, the wettability of obtained porous surfaces depending on the cell structures is systematically discussed. Finally, a super-hydrophobic surface with hierarchical micro-nanoscale roughness, low water adhesion, and high water-impact resistance is built by depositing nanoparticles on a porous surface. Consequently, this study offers a clean and simple method to prepare porous surfaces with adjustable cell structures, which is expected to open a door to developing a new fabrication technique for micro/nano-porous surfaces.