Impact of the coating process on the molecular structure of starch-based barrier coatings

Molecular analysis of starch structure can be used to explain and predict changes in physical properties, such as water vapor and oxygen barrier properties in packaging materials. Solution casting is a widely used technique to create films from starch formulations. This study compared the molecular properties of these standard films with those of experimental coatings applied to paper in laboratory-scale and pilot-scale trials, with all three techniques using the same starch formulation. The results revealed large differences in molecular structure, i.e., cross-linking and hydrolysis, between films and coatings. The main differences were due to the shorter drying time allowed to laboratory-scale coatings and the accelerated drying process in pilot trials owing to the high energy output of infrared dryers. Furthermore, surface morphology was highly affected by the coating technique used, with a rougher surface and many pinholes occurring in pilot-scale coatings, giving lower water vapor permeability than laboratory-scale coatings

Effect of amylose:amylopectin ratio and rice bran addition on starchfilms properties

The influence of the amylose:amylopectin ratio on the properties of pea, potato and cassava starch films and the effect of the incorporation of rice bran of two different particle sizes were studied. The structural, mechanical, optical and barrier properties of the films were analyzed after 1 and 5 weeks. The high content of amylose gave rise to stiffer, more resistant to fracture, but less stretchable films, with lower oxygen permeability and greater water binding capacity. Although no changes in the water vapour permeability values of the films were observed during storage, their oxygen permeability decreased. Throughout storage, films became stiffer, more resistant to break, but less stretchable. Rice bran with the smallest particles improved the elastic modulus of the films, especially in high amylose content films, but reduced the film stretchability and its barrier properties, due to the enhancement of the water binding capacity and the introduction of discontinuities.The authors acknowledge the financial support from the Spanish Ministerio de Economia y Competitividad throughout the project AGL2010-20694, co-financed with FEDER founds. Amalia Cano also thanks Spanish Ministerio de Educacion, Cultura y Deporte for the FPU grant.Cano Embuena, AI.; Jiménez Marco, A.; Cháfer Nácher, MT.; González Martínez, MC.; Chiralt Boix, MA. (2014). Effect of amylose:amylopectin ratio and rice bran addition on starchfilms properties. Carbohydrate Polymers. 111:543-555. https://doi.org/10.1016/j.carbpol.2014.04.075S54355511

Crystallinity and Morphology of Starch Polymers in Films

Starch is a renewable material that can be converted into biodegradable plastic products, or films with excellent oxygen barrier properties. Films of potato starch, amylose, amylopectin and blends thereof were made by solution casting. Their crystallinity, morphology, water content, thermal transitions and surface composition were studied and related to film composition and film formation conditions. <p />An increase in air humidity during film formation increased the crystallinity of starch films, whereas the crystallinity of amylose films was unaffected and amylopectin films were amorphous, as determined by wide-angle X-ray diffraction. Blending of amylose and amylopectin resulted in films with a considerably higher crystallinity than could be predicted. We propose that the reason for this is co-crystallization between amylose and amylopectin. Melting of co-crystals is suggested to give rise to an endotherm observed with differential scanning calorimetry. <p />The starch films and films with low amylose content were phase separated, with amylose domains in an amylopectin matrix. In films with high amylose content, the phase separation was prevented by the formation of a continuous network. Transmission electron microscopy of amylose rich films revealed an amylose network structure consisting of stiff strands and pores. Water is present in the pores, in the amorphous phase and in the crystalline structure. The water content of the films was therefore dependent both on the degree of crystallinity and on the morphology. Redistribution of water from crystalline regions and from network pores into the amorphous phase is suggested to be the reason for the lower glass transition temperature (T_g) observed after heating as compared to the initially observed T_g. <p />The film surfaces were covered with protrusions of nanometer size as observed with atomic force microscopy. These are proposed to be proteins, native in starch, that have migrated to the surface during film formation. The possibility of surface modification by gas plasma treatment was explored. <p />This research work provides broad knowledge of starch polymer behavior and inter-actions with water in films that can be used in the development of new and environmentally friendly plastic materials as well as in other areas with starch applications