Bamboo fiber-based water- and oil-proof cardboard with reversible thermochromic properties for fast food packaging

Abstract

The rapid development of street vendor economies has driven the popularity of fast food, mainly due to its inherent convenience. However, such foods are typically served at high temperatures, and existing packaging materials fail to allow consumers to effectively judge the temperature. This study developed thermochromic, water- and oil-proof cardboard specifically designed for fast food packaging. The coating, consisting of sodium alginate (SA), hydroxypropyl methylcellulose (HPMC), polyvinyl butyral (PVB), and ethyl cellulose (EC), was applied to the cardboard, coupled with a thermochromic material (TC) incorporating crystal violet lactone (CVL), bisphenol A (BPA), and stearyl alcohol. The resultant cardboard exhibited outstanding water- and oil-proof properties. The enhanced oil resistance was attributable to hydrogen bonding between SA and HMRC, as well as cross-linking between SA/HPMC and calcium ions (Ca²⁺) in the base paper. The PVB/EC coating further reinforced the cardboard's waterproofing and mechanical properties through additional hydrogen bonding. In thermochromic tests, the cardboard displayed a significant color change, transitioning from dark blue to colorless as the temperature increased from 30 °C to 55 °C. Overall, this research developed a bamboo-fiber-based food packaging cardboard with superior water- and oil-proof, and thermochromic properties.