Effect of Operational Variables on Supercritical Foaming of Caffeic Acid-Loaded Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends for the Development of Sustainable Materials

Expanded polystyrene will account for 5.3% of total global plastic production in 2021 and is widely used for food packaging due to its excellent moisture resistance and thermal insulation. However, some of these packages are often used only once before being discarded, generating large amounts of environmentally harmful plastic waste. A very attractive alternative to the conventional methods used for polymer processing is the use of supercritical carbon dioxide (scCO2) since it has mass-transfer properties adapted to the foam morphology, generating different path lengths for the diffusion of active compounds within its structure and can dissolve a wide range of organic molecules under supercritical conditions. The objective of this research was to evaluate the effect of operational variables on the process of caffeic acid (CA) impregnation and subsequent foaming of polylactic acid (PLA) as well as two PLA/poly(butylene-co-terephthalate-adipate) (PBAT) blends using scCO2. The results showed an increase in the degree of crystallinity of the CA-impregnated samples due to the nucleation effect of the active compound. On the other hand, SEM micrographs of both films and foams showed significant differences due to the presence of PBAT and its low miscibility with PLA. Finally, the results obtained in this work contribute to the knowledge of the important parameters to consider for the implementation of the impregnation and foaming process of PLA and PLA/PBAT blends with potential use in food packaging.

Extrusion of Porous Protein-Based Polymers and Their Liquid Absorption Characteristics

The production of porous wheat gluten (WG) absorbent materials by means of extrusion processing is presented for the future development of sustainable superabsorbent polymers (SAPs). Different temperatures, formulations, and WG compositions were used to determine a useful protocol that provides the best combination of porosity and water swelling properties. The most optimal formulation was based on 50 wt.% WG in water that was processed at 80 °C as a mixture, which provided a porous core structure with a denser outer shell. As a green foaming agent, food-grade sodium bicarbonate was added during the processing, which allowed the formation of a more open porous material. This extruded WG material was able to swell 280% in water and, due to the open-cell structure, 28% with non-polar limonene. The results are paving the way towards production of porous bio macromolecular structures with high polar/non-polar liquid uptake, using extrusion as a solvent free and energy efficient production technique without toxic reagents.

Poly (lactic acid) blends: Processing, properties and applications

Poly (lactic acid) or polylactide (PLA) is a commercial biobased, biodegradable, biocompatible, compostable and non-toxic polymer that has competitive material and processing costs and desirable mechanical properties. Thereby, it can be considered favorably for biomedical applications and as the most promising substitute for petroleum-based polymers in a wide range of commodity and engineering applications. However, PLA has some significant shortcomings such as low melt strength, slow crystallization rate, poor processability, high brittleness, low toughness, and low service temperature, which limit its applications. To overcome these limitations, blending PLA with other polymers is an inexpensive approach that could also tailor the final properties of PLA-based products. During the last two decades, researchers investigated the synthesis, processing, properties, and development of various PLA-based blend systems including miscible blends of poly l-lactide (PLLA) and poly d-lactide (PDLA), which generate stereocomplex crystals, binary immiscible/miscible blends of PLA with other thermoplastics, multifunctional ternary blends using a third polymer or fillers such as nanoparticles, as well as PLA-based blend foam systems. This article reviews all these investigations and compares the syntheses/processing-morphology-properties interrelationships in PLA-based blends developed so far for various applications.

Characterization and mechanical properties of foamed poly(ɛ-caprolactone) and Mater-Bi blends using CO2 as blowing agent

Biodegradable foams are a key area of growth for packaging applications. Starch-based materials have been a successful environmentally degradable polymer. However, making foams out of these materials has been challenging due to their chemical composition and consequent low miscibility in CO2. We examine the potential for developing biodegradable foams with one component being a starch-based polymer by introducing it into polycaprolactone. Polycaprolactone has thus far shown very high-expansion ratios for foams with supercritical CO2. Blends with increasing amounts of starch-based materials were processed and foamed using isothermal treatments with supercritical CO2. Characterization of the samples was done using X-ray diffraction, differential scanning calorimetry, and scanning electron microscopy. The melting enthalpies and temperatures of the starch-based materials phase decreased with decreasing starch-based materials indicating some an influence of polycaprolactone on the starch-based materials crystallinity. Foaming, however, caused a reversal in this effect with the foamed melting points similar to the pure components. Micrographs of the samples from the scanning electron microscopy revealed that the cell size of the foams reduced with the increase in starch-based materials concentration. Mechanical tests—tensile, compression, shear, and impact—were performed on the foamed samples. The results indicate a valuable approach to foaming materials that are compostable but not CO2 miscible through blending with a highly foamable polymer such as polycaprolactone.

Aluminum hydroxide nanoparticles show a stronger vaccine adjuvant activity than traditional aluminum hydroxide microparticles

Aluminum hydroxide is used as a vaccine adjuvant in various human vaccines. Unfortunately, despite its favorable safety profile, aluminum hydroxide can only weakly or moderately potentiate antigen-specific antibody responses. When dispersed in an aqueous solution, aluminum hydroxide forms particulates of 1-20μm. There is increasing evidence that nanoparticles around or less than 200nm as vaccine or antigen carriers have a more potent adjuvant activity than large microparticles. In the present study, we synthesized aluminum hydroxide nanoparticles of 112nm. Using ovalbumin and Bacillus anthracis protective antigen protein as model antigens, we showed that protein antigens adsorbed on the aluminum hydroxide nanoparticles induced a stronger antigen-specific antibody response than the same protein antigens adsorbed on the traditional aluminum hydroxide microparticles of around 9.3μm. The potent adjuvant activity of the aluminum hydroxide nanoparticles was likely related to their ability to more effectively facilitate the uptake of the antigens adsorbed on them by antigen-presenting cells. Finally, the local inflammation induced by aluminum hydroxide nanoparticles in the injection sites was milder than that induced by microparticles. Simply reducing the particle size of the traditional aluminum hydroxide adjuvant into nanometers represents a novel and effective approach to improve its adjuvanticity.

Improving Melt Strength of Polylactic Acid

Melt strength of polylactic acid (PLA) was improved through various modifications including grafting, crosslinking, chain extension, blending, plasticizing and nucleation. The results showed that melt strength was increased, to varying degrees, by crosslinking, chain extension and blending. In addition, melt strain (detected by velocity) was increased by chain extension, blending with elastomer, and plasticizing, but was decreased by crosslinking. The molecular weights, thermal properties and viscosity of the modified PLAs were also studied to investigate the causes of the observed variations in melt strength. Viscosity results generally corresponded with that of melt strength, but not with that of melt strain. With the exception of plasticizing and nucleation, the modifications had no significant effect on the thermal properties of PLA. The molecular weight (in particular the extremely large molecules representing by Mz) and the polydispersity of PLA were significantly increased after crosslinking and chain extension, which accounts for the observed increase in melt strength.