Preparation of graphene by pressurized oxidation and multiplex reduction and its polymer nanocomposites by masterbatch-based melt blending

TLDR

The study develops a masterbatch strategy for dispersing graphene into poly(lactic acid) via melt blending and examines graphene’s heat and mass barrier effects on the composites’ thermal degradation and combustion. Graphene is synthesized from graphite using pressurized oxidation followed by multiplex reduction with ammonia and hydrazine, yielding single‑atom‑thick sheets that are incorporated into PLA through a masterbatch melt‑blending process. The resulting nanocomposites exhibit enhanced crystallinity, crystallization rate, mechanical strength, electrical conductivity, and fire resistance, with properties varying with graphene dispersion and loading and showing a percolation threshold at 0.08 wt % where reinforcing and reducing effects produce inflexions.

Abstract

Graphene is prepared from graphite by pressurized oxidation and multiplex reduction. The pressurized oxidation is advantageous in easy operation and size-control, and the multiplex reduction, based on ammonia and hydrazine, produces single-atom-thick graphene (0.4–0.6 nm thick) which can be directly observed by atomic force microscopy. A masterbatch strategy, which is feasible in "soluble" thermoplastic polymers, is developed to disperse graphene into poly(lactic acid) by melt blending. The graphene is well dispersed and the obtained nanocomposites present markedly improved crystallinity, rate of crystallization, mechanical properties, electrical conductivity and fire resistance. The properties are dependent on the dispersion and loading content of graphene, showing percolation threshold at 0.08 wt%. Graphene reinforces the nanocomposites but cuts down the interactions among the polymer matrix, which leads to reduced mechanical properties. Competition of the reinforcing and the reducing causes inflexions around the percolation threshold. The roles of the heat barrier and mass barrier effects of graphene in the thermal degradation and combustion properties of the nanocomposites are discussed and clarified.