Enhancement of Flame Retardancy and Mechanical Properties of Polylactic Acid with a Biodegradable Fire-Retardant Filler System Based on Bamboo Charcoal

Abstract

A cooperative flame-retardant system based on natural intumescent-grafted bamboo charcoal (BC) and chitosan (CS) was developed for polylactic acid (PLA) with improved flame retardancy and minimal decline in strength properties. Chitosan (CS) as an adhesion promoter improved the interfacial compatibility between graft-modified bamboo charcoal (BC-m) and PLA leading to enhanced tensile properties by 11.11% and 8.42%, respectively for tensile strength and modulus. At 3 wt.% CS and 30 wt.% BC-m, the crystallinity of the composite increased to 38.92%, or 43 times that of pure PLA (0.9%). CS promotes the reorganization of the internal crystal structure. Thermogravimetric analysis showed significantly improved material retention of PLA composites in nitrogen and air atmosphere. Residue rate for 5 wt.% CS and 30 wt.% BC-m was 29.42% which is 55.1% higher than the theoretical value of 18.97%. Flammability tests (limiting oxygen index-LOI and UL-94) indicated significantly improved flame retardancy and evidence of cooperation between CS and BC-m, with calculated cooperative effectiveness index(Ce) >1. From CONE tests, the peak heat release rate (pHRR) and total heat release (THR) were reduced by 26.9% and 30.5%, respectively, for 3% CS + 20% BC-m in PLA compared with adding 20% BC-m alone. Analysis of carbon residue morphology, chemical elements and structure suggest CS and BC-m form a more stable char containing pyrophosphate. This char provides heat insulation to inhibit complete polymer pyrolysis, resulting in improved flame retardancy of PLA composites. Optimal mix may be recommended at 20% BC-m + 3% CS to balance compatibility, composite strength properties and flame retardance.

Expanding Poly(lactic acid) (PLA) and Polyhydroxyalkanoates (PHAs) Applications: A Review on Modifications and Effects

“…Li et al [ 302 ] developed a cooperative flame-retardant system based on natural intumescent-grafted bamboo charcoal (BC) and chitosan (CS) for PLA. Figure 16 shows a schematic diagram of the composite preparation and testing.…”

“…Flammability tests (UL-94 V-0 rating and LOI of 33.6 vol.%) showed a substantial enhancement in flame retardancy. The reported composite is claimed to meet the requirements for strong, biodegradable and non-toxic PLA packaging products [ 302 ].…”

Mechanically Robust and Flame-Retardant Polylactide Composites Based on In Situ Formation of Crosslinked Network Structure by DCP and TAIC

“…As a common reinforcing material, natural fibers are also used to enhance the mechanical properties of flame-retardant PLA materials [26,27]. Commonly used fibers mainly include hemp fiber [28,29], wood fiber [30], bamboo fiber [31] and stem fiber [32].…”

Synthesis of P-/N-Containing Bamboo-Activated Carbon toward Enhanced Thermal Stability and Flame Retardancy of Polylactic Acid

“…The emergence of degradable plastics derived from renewable resources has provided a route to reduce the potential damage to the environment and health, and has gradually been an alternative to conventional polymers in various end uses. Polylactic acid (PLA) is one candidate that has attracted extensive academic interest and industrial attention for its excellent bio-compatibility and biodegradability, favorable processibility and abundance in raw material supply, which makes it ubiquitously used in food packaging, medical products, vehicle parts, 3D printing and the aerospace industry [ 4 , 5 , 6 , 7 ]. However, the inadequate thermal stability and easy degradation at high temperatures greatly hamper its perspective applications in electronics and various commercial fields.…”