Knowledge-based design of better biopolymers
Conventional polymers or plastics are made from petroleum-based materials and there is a push to find alternative biopolymers to do their jobs. In addition, the nanoceramic inorganic fillers commonly used to impart unique properties demonstrate low stability during processing and in service. The EU-funded project 'Novel nano-stabilisation for green bioplastic nanocomposites' (NANOSTAB-GB) delivered a solution to both problems. Scientists developed novel composites having enhanced thermal stability and durability based on the use of biopolymers and naturally occurring functionalised nanoclay fillers. Their smart stabilisation strategies for modifying the nanoclay with antioxidants induce reinforcing biopolymer-nanoclay networks. In one approach, NANOSTAB-GB researchers developed novel organic modifiers of clay containing an antioxidant or a (hindered amine) light stabiliser to inhibit polymer photo-oxidation. The modified clays were incorporated into the biopolymers polyamide (PA11) and polylactic acid (PLA) to produce novel biopolymer-clay nanocomposites. The new composites were more stable during thermal processing and accelerated ultraviolet exposure than the same polymers containing commercially available clay organic modifiers. In a second approach, scientists exploited a relatively new class of molecules, layered double hydroxides (LDHs). Positively charge layers are separated by an interlayer of weakly bound anions that can be replaced by a variety of negatively charged species. The team synthesised new LDH nanoparticles containing either an antioxidant or a light stabiliser. These were incorporated into PA11 and PLA. The novel biopolymer-based LDH nanocomposites were not as stable at high temperatures as composites with unmodified LDH but had better photo-oxidative stability in accelerated weathering tests. NANOSTAB-GB successfully prepared stable biopolymer-based functionalised-clay nanocomposites exploiting a sort of silver bullet or site-directed stabilisation mechanism. The innovative functionalised clay nanofillers, in addition to their nanofiller role, stabilised the nanocomposite. Being available on demand at the oxidation sites (the interface between polymer matrix and filler), they delivered maximum inhibition for improved long-term stability. The project has delivered an important route to stabilisation of polymers, bio or not, that employ clay nanofillers. Its new functionalised nanofillers with built-in stabilisation capabilities will improve the durability of many products. Taken together, outcomes have made an important contribution to a sustainable knowledge-based bio-economy for Europe.
Keywords
Biopolymers, nano-stabilisation, bioplastic, nanocomposites, nanoclay
