Over the years, the spread of plastics has largely contributed to progress and competitiveness in all industrial sectors. However, this trend, in addition to contributing to the progressive depletion of fossil resources, inevitably involves energy consumption, no longer sustainable in the current global emergency situation, significant carbon dioxide emissions related to manufacturing processes and highly responsible for climate change phenomena, as well as environmental disasters usually generated by improper management of end-of-life products.
These critical issues, particularly limiting in the context of the key points of the current ecological transition, have strongly influenced the research trends as demonstrated by an accentuated interest in bio-based raw materials [1–4], thermoplastic polymer systems being intrinsically recyclable [5, 6] and new zero-waste technologies [7, 8].
In this frame, several environmental friendly polymers were explored, including polyhydroxyalkanoates [9], poly (1,4-butylene succinate) [10] and polylactic acid [11]. In addition to their natural origin, these materials can be synthesized by microorganisms and, at the end of their life cycle, they can be degraded in environmental conditions. However, their potential range of applications is still limited due to lower performance and their relatively high cost compared to similar petrochemical resins.
Poly(lactic acid) (PLA) is a compostable aliphatic thermoplastic polyester produced by the polymerization of lactic acid, in turn, obtained from the fermentation of carbohydrates such as corn starch, sugar beet or sugar cane[12–16].Unfortunately, the potential employment prospects due to these peculiarities are still limited by some critical issuessuch as brittleness, low stiffness and thermal stability, very slow crystallization kinetics, poor melt strength often alleviated by adding specific additives such as plasticizers, chain extenders, tougheners, and so on. [17–19].
In this frame, interesting results are available by adding PLA with wood flours (FW), an important source of renewable biomass. Lv et al. have studied compounds containing 30% by weight of starch or wood flour and have demonstrated through artificial weathering tests that the inclusion of the filler enhances the durability of the matrix in outdoor applications [20]. This benefit has been attributedto a slowdown of the PLA structure breakdown thanks to screening effects exerted by the included fillers that would not allow ultraviolet rays and humidity to penetrate effectively and deeply into the polymer matrix.
In addition to using renewable biomass, other researchers have focused on the use of natural fibres deriving from processing waste of agricultural products typical of specific areas. Isadouneneet al. studiedthe effect of waste deriving from the milling of olives as a filler to have an economic component, available locally and avoid having to dispose of it by incineration [21]. Another example of the use of processing waste is offered by the study of Özdemiret al. [22], which analyzes the effect of a filler made from the processing waste of hazelnuts. In particular, the research considered the hazelnut husk (HH), an external fibrous component that, together with the shell, contains the hazelnut and is normally discarded during harvesting. This waste, usually destined for incineration, amounts to about 200,000 tons per year and can potentially be recovered as a filler to develop new plastic formulations.
In this work, PLA compounds filled with different amounts(up to 5% by weigth) of a food flour waste (FW)were explored in terms of thermal and mechanical properties as well as morphological aspects.
The interest in the recovery/recycling of food waste, otherwise destined for landfill or incineration, is clearly supported by aspects of environmental sustainability that can no longer be derogated from.
The results of the experimentation reported in this paper show that the inclusion of FW in a poly (lactic) acid gives rise to new compounds with improved mechanical strength and stiffness but lower toughness with respect to the reference matrix.