Incorporating biopolymers in packaging foams can contribute to a more circular packaging system, utilizing renewable and compostable materials. Gelatin, with its favorable physicochemical properties, allows for producing gelatin foams via mechanical foaming, a well-established and low-investment process. To improve foam properties, starch can be added to the gelatin formulation. However, the variability in the properties of starch powders can impact the polymer blend and, consequently, the properties of the dry foam. This study aimed to investigate the impact of different starch powders from different botanical origins (tapioca and corn) and treatments (native or pregelatinized) on the properties of gelatin–starch foams produced by mechanical foaming. The study successfully produced foams with densities of approximately 45–50 kg/m3 and compression properties comparable to EPS (expanded polystyrene) foams. The starch type and pre-treatment significantly influenced the properties of the foam. Pregelatinized starches exhibited slightly higher densities due to lower foamability caused by higher viscosity. Using starch exhibiting total loss of birefringence led to denser foams with greater compression properties than those with starch with a certain degree of crystallinity remaining. Therefore, selecting the appropriate starch type is crucial when developing starch-based materials to ensure optimal material and processing properties align with application requirements.

Although most cellular polymers are made from thermoplastics using different foaming technologies, gelatin and many other natural polymers can form hydrogels and convert them to cellular solids using various techniques, many of which differ from traditional plastic foaming, and so does their resulting structures. Cellular solids from natural hydrogels are porous materials that often exhibit a combination of desirable properties, including high specific surface area, biochemical activity, as well as thermal and acoustic insulation properties. Among natural hydrogels, gelatin-based porous materials are widely explored due to their availability, biocompatibility, biodegradability and relatively low cost. In addition, gelatin-based cellular solids have outstanding properties and are currently subject to increasing scientific research due to their potential in many applications, such as biocompatible cellular materials or biofoams to facilitate waste treatment. This article aims at providing a comprehensive review of gelatin cellular solids processing and their processing-properties-structure relationship. The fabrication techniques covered include aerogels production, mechanical foaming, blowing agents use, 3D printing, electrospinning and particle leaching methods. It is hoped that the assessment of their characteristics provides compiled information and guidance for selecting techniques and optimization of processing conditions to control material structure and properties to meet the needs of the finished products.

Gelatin hydrogels are widely used materials that may require surfactants to adjust their solution’s surface tension for cell attachment, surface adsorption enhancement, or foaming. However, gelatin is a highly surface-active polymer, and its concentrated solutions usually do not require surfactants to achieve low surface tension. However, anionic surfactants, such as sodium dodecyl sulfate (SDS), interact strongly with gelatin to form complexes that impact its hydrogels’ rheological properties, influencing processability and functionality. Nevertheless, there is a lack of systematic research on the impact of these complexes on high gelatin content (i.e., high strength) hydrogels’ rheological properties. In this work, the SDS/gelatin ratio-dependent viscoelastic properties (e.g., gel strength, gelation kinetics, and melting/gelling temperature) of high-strength gelatin hydrogels were investigated using rheology and correlated to surface tension, viscometry, FTIR, and UV-Vis spectrophotometry. SDS–gelatin ratio was proved to be an important factor in tailoring the rheological properties of gelatin hydrogels. The gel strength, gelation kinetics, and melting/gelling temperature of the gelatin hydrogels linearly increased with SDS incorporation up to a maximum value, from which they started to decline. The findings of this work have wide applicability in tailoring the properties of gelatin–SDS solutions and hydrogels during their processing.

The effects of poly(butylene adipate-co-terephthalate) (PBAT) on crystallization behavior and morphology of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied to provide the useful information to control and improve PHBV processing. PHBV were blended with 15, 30 and 50 wt% PBAT by twin screw extrusion and these were subsequently compared to unblended PHBV. The rate of crystal development determined from differential scanning calorimetry (DSC) at 120 °C showed that the incorporation of PBAT retarded the crystal growth rate. Moreover, the crystal structure of polymer blends was examined by X-ray diffraction (XRD) and the results revealed that PBAT did not affect the crystal structure of PHBV. The responses of the melt-crystallized PHBV to different quantities of PBAT were recorded by polarized optical microscopy (POM). The results demonstrated that the size of spherulite dramatically increased when 15 wt% PBAT was added and the shape of spherulite was imperfect when PBAT reached 30 wt%. The morphologies of PHBV and its blends on the freeze-fractured specimens were exposed using scanning electron microscopy (SEM). The SEM images revealed the phase separation of PHBV/ PBAT blends in any composition. The morphology of 15 and 30 wt% PBAT presented droplet in matrix morphology and changed to co-continuous morphology at 50 wt% PBAT.

The effects of poly(butylene adipate-co-terephthalate) (PBAT) on crystallization behavior and morphology of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied to provide the useful information to control and improve PHBV processing. PHBV were blended with 15, 30 and 50 wt% PBAT by twin screw extrusion and these were subsequently compared to unblended PHBV. The rate of crystal development determined from differential scanning calorimetry (DSC) at 120 °C showed that the incorporation of PBAT retarded the crystal growth rate. Moreover, the crystal structure of polymer blends was examined by X-ray diffraction (XRD) and the results revealed that PBAT did not affect the crystal structure of PHBV. The responses of the melt-crystallized PHBV to different quantities of PBAT were recorded by polarized optical microscopy (POM). The results demonstrated that the size of spherulite dramatically increased when 15 wt% PBAT was added and the shape of spherulite was imperfect when PBAT reached 30 wt%. The morphologies of PHBV and its blends on the freeze-fractured specimens were exposed using scanning electron microscopy (SEM). The SEM images revealed the phase separation of PHBV/ PBAT blends in any composition. The morphology of 15 and 30 wt% PBAT presented droplet in matrix morphology and changed to co-continuous morphology at 50 wt% PBAT.

Plastic litter is encountered in aquatic ecosystems across the globe, including polar environments and the deep sea. To mitigate the adverse societal and ecological impacts of this waste, there has been debate on whether ‘biodegradable' materials should be granted exemptions from plastic bag bans and levies. However, great care must be exercised when attempting to define this term, due to the broad and complex range of physical and chemical conditions encountered within natural ecosystems. Here, we review existing international industry standards and regional test methods for evaluating the biodegradability of plastics within aquatic environments (wastewater, unmanaged freshwater and marine habitats). We argue that current standards and test methods are insufficient in their ability to realistically predict the biodegradability of carrier bags in these environments, due to several shortcomings in experimental procedures and a paucity of information in the scientific literature. Moreover, existing biodegradability standards and test methods for aquatic environments do not involve toxicity testing or account for the potentially adverse ecological impacts of carrier bags, plastic additives, polymer degradation products or small (microscopic) plastic particles that can arise via fragmentation. Successfully addressing these knowledge gaps is a key requirement for developing new biodegradability standard(s) for lightweight carrier bags.

The effects of calcium carbonate (CaCO3) concentration on crystallization behaviors and morphology of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were investigated. Composites of PHBV with CaCO3 were prepared with filler loadings of low (5%wt) and high concentration (20%wt) and these were subsequently compared to unloaded PHBV. The morphologies of PHBV composites on the freeze-fractured specimens were examined using scanning electron microscopy (SEM). The SEM images revealed that increasing concentration of CaCO3 resulted in agglomeration. This agglomeration might affect crystal growth rate and mechanism. The crystal growth behavior of melt-crystallized PHBV with different amounts of CaCO3 was studied by polarized optical microscopy (POM), while the crystal structure was examined by X-ray diffraction (XRD). The rate of crystal growth determined from POM at selected crystallization temperatures revealed that the addition of a small amount of CaCO3 accelerated crystal growth rate, whereas excess amount of CaCO3 had the opposite effect. The POM images were also used to illustrate the change of crystal growth process presence of CaCO3. The unloaded PHBV clearly showed nucleation and growth mechanism, while PHBV composites displayed nucleation and then combination of crystals during the growth process. However, CaCO3 did not affect the crystal structureof any PHBV composite as observed by XRD. Molecular weight determination via gel permeation chromatography (GPC) indicated that there was no significant difference among PHBV composites.

The crystal growth rate of melt-crystallized poly (3-hydroxybutyrate- co -3-hydroxyvalerate) (PHBV) reacting with epoxy-functionalized chain extender was investigated by wide angle X-ray diffraction and polarized optical microscopy (POM). The maximum concentration of chain extender in this work was limited to 1.00 % wt for food contact considerations. The WAXD results revealed that the quantity of chain extender used in this study had no effect on crystal structure and all chain-extended PHBV had a PHB-type crystal structure. The rate of crystal growth determined from POM at various crystallization temperatures confirmed that the addition of epoxy-functionalized chain extender delayed the crystal growth rate but did not change the crystal growth process and morphology.

The present paper reports work in development of biocomposite boards compression moulded from wheat straw. Unlike most traditional wood based fibre/chip boards with addition of adhesives or bonding agents, attempt was made to utilise the lignin–hemicellulosic natural resin within straw as bonding agent, resulting in a class of ‘binderless’ and more natural biocomposite boards. The effects of straw preparation and compression moulding conditions on structural and mechanical properties of the binderless straw boards were studied systematically in terms of size of chopped straw, pretreatment and the combination of pressure and temperature during compression moulding. The bonding mechanisms of the natural resin in the straw biocomposites were investigated in terms of its mobilisation using NaOH pretreatment of straw and its redistribution to the straw interfaces during compression moulding process. Without any fractionation of straw or any additional adhesive bonding agent, the mechanical properties of the binderless straw boards were comparable to some commercially available wood and straw board products using addition of adhesives.

This paper reports work on extrusion foaming of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a chemical blowing agent based on sodium bicarbonate and citric acid and calcium carbonate nucleation agent. It includes investigations in the effects of rheological behaviour of the polymer, blowing agent, nucleation agent and processing conditions on the foam density and morphology. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is a natural biodegradable polyester with high crystallinity, low melt viscosity and slow crystallisation rate and high sensitivity to the thermal degradation at temperatures above its melting point, making it particularly difficult to control the foaming process. Use of negative gradient temperature profile was found beneficial to minimise the thermal degradation and achieve necessary melt strength to stabilise the cell structure. Solidification of the super-cooled polymer melt occurring at the die was discussed in relation to the selection of the temperature profile and rheological behaviour and solidification of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) characterised by rotational rheometry. In addition to extrusion foaming conditions, effect of the blowing and nucleation agents on rheology of the polymer, the cell refinement on foam density and morphology were discussed. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was extruded with a twin screw extruder fitted with a strand die yielding up to 60% density reduction with uniform fine cell structure.

The thermo-mechanical performance of extruded wheat starch/flour containing different additives was examined via microwave-heated thermo-mechanical analysis. Additionally, the dielectric property of the wheat starch-based materials was also studied using a microwave calorimeter. It has been found that when glycerol or polyvinyl alcohol was used as single additive in wheat starch, a content limit existed and using the additives at a concentration higher than the limit will lead to deterioration of the material’s microwave foamability. A good initial thermal expansion is essential for a proper foaming of the wheat starch-based materials; however, high enough dielectric loss factor (ɛ″) is also required for the formation of foam structure under microwave radiation. Glass transition temperature ( Tg) for the extruded wheat starch materials was detected by microwave thermo-mechanical analysis at about 75–95°C when heated at 15°C/min; and for the foamable formulations, the foaming temperature ( Tf) is generally 10–20°C higher than the corresponding Tg. Impurities like proteins play important roles in the microwave foaming of extruded wheat flour. Overall, the extruded wheat flour with additives is more difficult to foam under microwave heating than the wheat starch extruded from the similar formulations.

Extruded pellets from starch-based materials have been heated and foamed under microwave radiation. The foaming mechanisms and effects of some additives on the dielectric properties of the materials have been investigated using a microwave calorimeter. A rapid increase in dielectric loss factor (ɛ″) has been found for all the tested materials foamable under microwave heating and the onset of the ɛ″ increase is considered to be correlated to glass transition. It has been found that extruded starch materials can be foamed at 15℃/min but the expansion level reduced compared with that of the same material foamed at higher heating rate. The incorporation of organic additives in starch-based materials generally led to significant decrease of their microwave foamability when glycerol and polyvinyl alcohol are used as the additives in the extruded pellets.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a semi-polycrystalline biopolymer from the polyhydroxyalkanonate family has in recent years become a commercial bioplastic with mechanical properties comparable to isotactic polypropylene and enhanced O2, CO2 and H2O barrier properties. However, its brittleness and sensitivity to thermal and hydrolysis degradations restrict its applications. To overcome the problems associated with degradation during processing blending of PHBV and an epoxy-functionalized chain extender (Joncryl® ADR-4368 S) was conducted in a twin screw extruder. The effect of concentration of the chain extender on thermal, crystallization and rheological behaviours of PHBV was investigated. Thermal gravimetric analysis results indicated improvement in the resistance to thermal decomposition of PHBV by introducing the chain extender. This was accompanied with calculation of thermal degradation activation energy (Ea) using the Flyn–Walls–Ozawa method which confirmed increase of Ea with the increase in content of the chain extender. The rheological behaviour and crystallization of modified PHBV was characterized by rotational rheometry and differential scanning calorimetry techniques, respectively. The results show that addition of chain extender enhanced viscosity of PHBV and also reduce the rate of crystallization.

在恒温恒湿条件下对发泡聚乙烯醇（PVOH）试样吸收水、酒精的特性进行了测试分析．结果表明：发泡PVOH试样在承受一定压力的情况下吸水性能略有降低；试样被压缩至8000N后平衡吸水量明显升高；试样自然吸收酒精量约为自然吸水量的5．2倍；吸收酒精后，试样尺寸约增加了20％；压缩至8000N后，再做吸酒精试验，其平衡吸酒精量基本不变，且达到吸收平衡的时间缩短．

This paper presents an assessment of the technical and environmental performance of a wheat-based foam (WBF) and bio-composite for shipping chilled products. The thermal conductivity of the WBF was found to be higher than that of polyurethane foams commonly used in high-value insulation packaging, but close to that of low-density (expanded polystyrene) EPS foams and significantly lower than that of polyethylene (PE) foams, which are typically used in thermal packaging of foods. The insulation performance of a simple cool box constructed from both the WBF and EPS sandwich panels without the use of any refrigerant was studied experimentally. The comparison demonstrated that the performance of the WBF cool box was comparable to that of the EPS counterpart Two industrial case studies were conducted on WBF cool boxes with refrigerants in comparison with PE or EPS counterparts The WBF cool boxes had comparable thermal performance to the EPS and PE counterparts on the basis of identical foam thickness. The performance of the WBF cool boxes was also simulated with finite element (FE) modelling. Good agreement was achieved between experimental data and the FE prediction. The model was then used to assist cool box design. WBF cool boxes made from renewable raw materials are inherently biodegradable and may be used as an alternative to those based on polymer foams in thermal packaging applications. Life-cycle assessment (LCA) was used to investigate environmental profiles of cool boxes made with WBF, EPS and PE foams. The WBF cool boxes offer substantially lower global warming and abiotic depletion potentials than equivalent cool boxes made from petrochemical foams. Copyright (C) 2010 John Wiley & Sons, Ltd.

A study on structural and mechanical properties of bio-composites based on wheat straw and wheat flour is reported with a view to using these low-cost raw materials for the preparation of fully bio-based and biodegradable composites for non-structural applications. The wheat straw was pre-treated with sodium hydroxide and fractionated in a twin screw extruder. Chopped straw was also used for comparison purposes. The straw was then extrusion compounded with wheat starch where plasticisation and gelatinisation of the matrix took place. Microstructure and mechanical properties of the compression moulded compounds were examined. The wheat straw formed good adhesion with the matrix which lead to enhanced mechanical properties. Refinement of the straw contributed to the exposure of the straw fibre surfaces. This led to an increase in flexibility and packing efficiency of the straw fibre thus giving a high tensile strength and ductility of the composites. Composites containing untreated chopped straw also displayed comparable mechanical properties and these materials are more cost-competitive alternatives to those containing the refined straw fibre.

This paper reports work in the extrusion fractionation of wheat straw and biocomposites utilising the entire constituents of straw. The effects of pre-treatment and extrusion conditions on fractionation of straw and mechanical properties of the biocomposites were studied systematically. It is demonstrated that twin screw extrusion can be used for effective fractionation of straw feedstock for production of biocomposites utilising the natural resin and fibre reinforcement without additional polymeric resin. In comparison with the conventional approaches where cellulose is extracted and compounded with resins, the self-reinforced biocomposites benefit from low material and processing costs as well as lower environmental impacts.

Using a method known as regular packing and stacking (RPS) technology, starch foams made by extrusion foaming of wheat flour can be converted by self-adhesion to produce bulk foams of any required sizes for much more broad applications. These block foams are reinforced by a network of the bonding interfaces and hence can be regarded as macrocomposites. The influence of the reinforcing interfaces on compression behavior of the RPS blocks was investigated by mechanical testing of foams with different geometry of the interface network and interface thickness. It is demonstrated that the interface network of the block foams can be designed to manipulate the macrostructure and compression behavior of the foam for protective packaging.

Extruded pellets made from wheat flour and purified wheat starch were expanded by applying microwave heating within moulds, a method known as microwave-assisted moulding (MAM). Selection of adequate mould material, pre-treatment of pellets and control of the initial loading of pellets in the mould cavity were found to be the key issues to achieve a uniformly foamed block with good integrity. Polytetrafluoroethylene (PTFE) was found to be an appropriate mould material for the MAM process. The bonding between foamed pellets in a block can be significantly enhanced by soaking the pellets in a NaCl solution before microwave foaming. There exists an optimum initial loading of pellets in the mould for a given pellet formulation, which allows sufficient expansion to achieve an acceptable extent of interfacial bonding and mould filling. The work demonstrated the feasibility of moulding starch block foams and potential applications of the foams in packaging and lightweight composites.