Microstructure and physical properties of thermoplastic corn starch foams as influenced by polyvinyl alcohol and plasticizer contents

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives

The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.

Evaluating how avocado residue addition affects the properties of cassava starch-based foam trays

Avocado seed (AS) is an interesting residue for biopackaging because it has high starch content (41 %). We have prepared composite foam trays based on cassava starch containing different AS concentrations (0, 5, 10 and 15 % w/w) by thermopressing. Composite foam trays with AS were colorful because this residue contains phenolic compounds. The composite foam trays 10AS and 15AS were thicker (2.1-2.3 mm) and denser (0.8-0.9 g/cm³), but less porous (25.6-35.2 %) than cassava starch foam (Control). High AS concentrations yielded composite foam tray less puncture resistant (~40.4 N) and less flexible (0.7-0.9 %), but with tensile strength values (2.1 MPa) almost similar to the Control. The composite foam trays were less hydrophilic and more water resistant than control due to the presence of protein, lipid, and fibers and starch with more amylose content in AS. High AS concentration in composite foam tray decreases the temperature of thermal decomposition peak corresponding to starch. At temperatures >320 °C the foam trays with AS were more resistant to the thermal degradation due to the presence of fibers in AS. High AS concentrations delayed the degradation time of the composite foam trays by 15 days.

The Use of New Waste-Based Plasticizer Made from Modified Used Palm Oil for Non-Glutinous Thermoplastic Starch Foam

A novel waste-based plasticizer derived from modified used palm oil (mUPO) was successfully developed and has been used as a new plasticizer to non-glutinous thermoplastic starch foam to improve their properties. The molecular weight and hydroxyl number of the mUPO was 3150 g/mol and 192.19 mgOH/g, respectively. The effects of mUPO content ranging from 0 to 9 phr were investigated. The results revealed that the optimal mUPO content as an additive was 6 wt%. The addition of mUPO had a direct effect on the mechanical properties and thermal properties. The impact strength increased from 1.30 to 4.55 J/m, while the glass transition temperature (T_g) decreased from 70.83 to 66.50 °C by increasing mUPO from 0 phr to 6 phr in the thermoplastic starch foam. The mUPO, on the other hand, has also the potential to reduce shrinkage from 33.91 to 21.77% and moisture absorption from 5.93 to 1.73% by increasing the content from 0 phr to 6 phr in starch foam. Furthermore, the mUPO helps the forming of the foam structure as measured by SEM, and the mUPO utilization of waste-based material could be a promising green alternative plasticizer for starch components, especially starch foam applications.

Thermoplastic starch nanocomposites: sources, production and applications - a review

The development of materials based on thermoplastic starch (TPS) is an excellent alternative to replace or reduce the use of petroleum-derived polymers. The abundance, renewable origin, biodegradability, biocompatibility, and low cost of starch are among the advantages related to the application of TPS compared to other thermoplastic biopolymers. However, through the literature review, it was possible to observe the need to improve some properties, to allow TPS to replace commonly used polyolefins. The studies reviewed achieved these modifications were achieved by using plasticizers, adjusting processing conditions, and incorporating fillers. In this sense, the addition of nanofillers proved to be the main modification strategy due to the large number of available nanofillers and the low charge concentration required for such improvement. The improvement can be seen in thermal, mechanical, electrical, optical, magnetic, antimicrobial, barrier, biocompatibility, cytotoxicity, solubility, and swelling properties. These modification strategies, the reviewed studies described the development of a wide range of materials. These are products with great potential for targeting different applications. Thus, this review addresses a wide range of essential aspects in developing of this type of nanocomposite. Covering from starch sources, processing routes, characterization methods, the properties of the obtained nanocomposites, to the various applications. Therefore, this review will provide an overview for everyone interested in working with TPS nanocomposites. Through a comprehensive review of the subject, which in most studies is done in a way directed to a specific area of study.