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<p>This study investigates the development of biodegradable starch-based foams as sustainable alternatives to petroleum-derived packaging materials. Foam samples were prepared from high-amylose corn starch and potato starch using chitosan and sodium trimetaphosphate (STMP) to promote crosslinking, and two processing routes – twin-screw extrusion and microwave expansion – were systematically compared. The influence of glycerol plasticization on foam morphology, mechanical performance, and aqueous stability was also evaluated. Key parameters such as density, compressive modulus, solubility, solution uptake, microstructure, and crystallinity were characterized. Results showed that microwave-expanded potato starch foams exhibited the lowest density of 0.1073&#xa0;g/cm<sup>3</sup> but the highest compressive modulus of 2688&#xa0;kPa, attributed to their fine, uniform pore structure and dense outer skin formed during rapid volumetric heating. Extruded corn starch foams with 5% glycerol exhibited higher densities of 0.4844&#xa0;g/cm<sup>3</sup> and mechanical stiffness due to reduced cell expansion and stronger cell wall integrity. Comparison of potato starch foams produced by extrusion and microwave expansion showed that the extruded foam had a density of 0.2133&#xa0;g/cm³, representing a 98.8% increase relative to the microwave-expanded foam. Scanning electron microscopy revealed significant differences in foam morphology between processing methods, with microwave-expanded foams displaying more uniform cell structures. X-ray diffraction (XRD) analysis confirmed that both extrusion and microwave expansion disrupted the native crystalline structure of starch, producing predominantly amorphous foams. Minor crystalline peaks associated with chitosan and retrogradation appeared only in selected extruded formulations. Glycerol plasticization effectively reduced foam brittleness but increased solubility and decreased water uptake capacity due to structural softening. These findings demonstrate that processing method plays a critical role in decoupling density and mechanical performance in starch-based foams, and identifies the potential of starch–chitosan-based composites, particularly those produced via microwave expansion, as viable, tunable candidates for biodegradable packaging applications.</p>

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Biodegradable Starch Foams with Tunable Properties: A Comparative Study of Microwave and Extrusion Processing

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月24日

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  • Caini Chen,
  • Apoorva Kulkarni,
  • Ramani Narayan,
  • Jeffrey M. Catchmark

摘要

This study investigates the development of biodegradable starch-based foams as sustainable alternatives to petroleum-derived packaging materials. Foam samples were prepared from high-amylose corn starch and potato starch using chitosan and sodium trimetaphosphate (STMP) to promote crosslinking, and two processing routes – twin-screw extrusion and microwave expansion – were systematically compared. The influence of glycerol plasticization on foam morphology, mechanical performance, and aqueous stability was also evaluated. Key parameters such as density, compressive modulus, solubility, solution uptake, microstructure, and crystallinity were characterized. Results showed that microwave-expanded potato starch foams exhibited the lowest density of 0.1073 g/cm3 but the highest compressive modulus of 2688 kPa, attributed to their fine, uniform pore structure and dense outer skin formed during rapid volumetric heating. Extruded corn starch foams with 5% glycerol exhibited higher densities of 0.4844 g/cm3 and mechanical stiffness due to reduced cell expansion and stronger cell wall integrity. Comparison of potato starch foams produced by extrusion and microwave expansion showed that the extruded foam had a density of 0.2133 g/cm³, representing a 98.8% increase relative to the microwave-expanded foam. Scanning electron microscopy revealed significant differences in foam morphology between processing methods, with microwave-expanded foams displaying more uniform cell structures. X-ray diffraction (XRD) analysis confirmed that both extrusion and microwave expansion disrupted the native crystalline structure of starch, producing predominantly amorphous foams. Minor crystalline peaks associated with chitosan and retrogradation appeared only in selected extruded formulations. Glycerol plasticization effectively reduced foam brittleness but increased solubility and decreased water uptake capacity due to structural softening. These findings demonstrate that processing method plays a critical role in decoupling density and mechanical performance in starch-based foams, and identifies the potential of starch–chitosan-based composites, particularly those produced via microwave expansion, as viable, tunable candidates for biodegradable packaging applications.