Coated with hydrophobic substances starch based foam tray production

The usage of expanded polystyrene trays in food packaging and service has become widespread especially in recent years due to its lightness and cheapness. However, its usage has begun to be banned or restricted in many parts of the world due to its negative effects on the environment. In recent years, many studies have been carried out on the production of biodegradable foam trays. Although starch-based foam trays show great promise in terms of being biodegradable and having sufficient mechanical resistance, their inadequate resistance to water is one of the most important obstacles in the spread of commercial use. In this study, the 35% starch suspensions were prepared from wheat starch or a mixture of wheat-potato starch cross-linked with glyoxal, 0,5% guar gum, 7% wheat fiber were added to the suspensions, and then foam trays were produced by baking. To increase the water-resistance of the trays, the trays were coated using polylactic acid (PLA), polycaprolactone (PCL), and polymethyl methacrylate (PMMA) solutions. Coating solutions were prepared by dissolving PLA and PCL in chloroform and by dissolving the PMMA solution in benzene. Densities, percentage water absorption amounts, and rates, mechanical properties of the uncoated and coated foam trays were determined. The surface of the coated trays was examined with Fourier Transform Infrared Spectrometer (FT-IR), The surface and cross-sections of the foam were imaged under the scanning electron microscope (SEM). The percent weight loss and visual changes of the foam tray pieces embedded in the simulated soil were observed. While the density of foam trays is not affected by the starch source, it was founded that the coating materials significantly (p<0,05) affected and increased the density of the trays. The average percentage water absorptions of the foam trays produced from wheat and wheat-potato starch were determined as 50% and 53%, respectively, and the difference between them was not statistically significant. The average percentage water absorption of foam trays coated with PLA (12%) and PMMA (8%) decreased significantly (p<0,01). The avarage water absorption rate of the uncoated trays was 8,413 g/min, and the coating application significantly reduced the water absorption rate of the trays. The water absorption rates of the samples coated with PCL, PLA, and PMMA were 1,783 g/min, 0,247 g/min and, 0,014 g/min, respectively, and especially the PMMA coating reduced the water absorption rate of the samples most effectively. The bending strength (1,848 MPa) and elastic modulus (66,026 MPa) of foam trays made of wheat starch were found to be higher than the bending strength (1,388 MPa) and elastic modulus (50,598 MPa) of the foam trays produced from wheat-potato starches. It was found that the flexural strength of trays coated with PLA (1,525 MPa) was similar to that of uncoated trays (1,180 MPa), while the bending strength of trays coated with PMMA (1,801 MPa) and PCL (1,967 MPa) was statistically significantly higher than that of uncoated trays. FT-IR analysis showed that the coating materials successfully coated the surfaces of starch-based foam trays. The Surface SEM images showed that the trays made of wheat-potato starch had less surface cracks, fewer pores and smaller pore diameters than the trays made of wheat starch. The coating materials filled the cracks and pores on the tray surfaces, so the density, bending strength, elastic modulus of the trays increased, the percentage and rate of water absorption of the trays decreased. The average coating thicknesses of PCL, PLA, and PMMA from cross-section SEM images were measured as 48,37 µm, 29,93 µm, and 44,07 µm, respectively. It was observed that the uncoated trays embedded in the simulated soil were disintegrated on the 3rd day, PCL coated trays on the 42nd day, and the trays coated with PLA on the 84th day. It was determined that the trays coated with PMMA were disintegrated at an average rate of 95% on the 120th day. It was concluded that the trays that will take the longest time to completely disintegrate under the tested composting conditions are those coated with PMMA, regardless of the starch source.