Abstract
Even though casein has an intrinsic potential ability to act as a flame retardant (FR) additive, the research regarding the FR performance of casein filled polymeric composites has not been thoroughly conducted. In the present work, two commercial casein products, such as lactic casein 720 (LAC) and sodium casein 180 (SC), were chosen to investigate their effects on the performances of the polypropylene (PP) composites. The melt compounding and compression moulding processes were employed to fabricate these casein-based composites. Ammonium polyphosphate (APP) was also selected to explore its combined effects in conjunction with casein on the composite’s flammability. The cone calorimeter results showed that the addition of casein significantly reduced (66%) the peak heat release rate (PHRR) of the composite compared to that of neat PP. In particular, the combination of LAC and APP led to the formation of more compact and rigid char compared to that for SC based sample; hence, a further reduction (80%) in PHRR and self-extinguishment under a vertical burn test were accomplished. Moreover, the tensile modulus of the composite improved (23%) by the combined effects of LAC and APP. The overall research outcome has established the potential of casein as a natural protein FR reducing a polymer’s flammability.
Highlights
The usage of natural materials in the composites field has become vital because of the growing needs for sustainable production, coupled with the increasing environmental awareness [1]
The effect of casein on Tc can be identified in PP-15APP-20LAC composite since the incorporation of 20 wt% lactic casein 720 (LAC) in PP-15APP promotes an increase of Tc of the composite (128.1 ◦ C) in comparison with that of PP-15APP (126.8 ◦ C)
The melting point of PP-15APP-20LAC composite indicated that the effect of ammonium polyphosphate (APP) on an increase in Tm is more dominant than casein as APP has the long-chain linked by covalent bonds, as opposed to the shell structure of casein micelles
Summary
The usage of natural materials in the composites field has become vital because of the growing needs for sustainable production, coupled with the increasing environmental awareness [1]. The potential of protein-based fibres to reduce flammability of fabrics and polymers have been explored [2]. Keratinous fibres (fibrous proteins), such as wool and chicken feather fibres, have been used as reinforcements to improve mechanical and fire-resistant properties of composites. Poly(lactic) acid and polyurethane composites with chicken feather fibres have demonstrated improved char formation and higher limiting oxygen index [7,8]. Globular proteins, such as casein and hydrophobin, have not been investigated in the context of composites These proteins have mostly been used in the food industry to improve flavour or texture of daily products. Even though casein has the effective residue forming ability under heating, the protein has not been employed to investigate its effects on the flammability of polymeric composites. The effects of LAC on the mechanical properties of the composites have been evaluated by conducting tensile tests
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