1. Introduction
In recent years, the large increase in world population, combined with the need to improve lifestyles, has led to a dramatic increase in polymer consumption [
1,
2,
3].
Fossil-derived polymers make a significant contribution to the anthropogenic carbon dioxide emission released to the environment. This contribution derives from all the steps of the life of the polymer: extraction of the oil, cracking, polymerization, processing and end of life [
4,
5]. The decarbonization of plastics can be achieved through two important steps: use of bio-based, or at least partly bio-based, polymers and recycling of these bio-based polymers. The end of life of these polymers, both through biodegradation or through combustion to recover energy, does not put new carbon dioxide in the environment and, rather, carbon dioxide is used for the production of the biomasses to be used for bio-based polymers. Moreover, the mechanical recycling [
6,
7], extending the life of the polymers, can, in its turn, make a significant contribution to a decrease in the huge amounts of plastics.
To date, although the recycling of conventional polymers is quite well researched [
8,
9,
10,
11], there is less research on the recycling of biodegradable polymers.
In our previous work [
12], the rheology of biodegradable poly(butylene adipate-co-butylene terephthalate) (PBAT) blends subjected to multiple extrusion cycles, as well as the mechanical properties, was studied. The results showed that the conditions used had no significant effect on the rheological and mechanical properties of the sample; therefore, the material was considered reusable. Similar studies on poly(lactic acid) (PLA) [
13,
14,
15] showed that it is possible to obtain recycled PLA with good properties only by adding small amounts of additives during mechanical recycling. The study by Bruzaud et al. [
16] showed that PLA is more stable than PHBV and, also, when blended with PHBV, shows more stability than pure PHBV in terms of recyclability. La Mantia et al. [
17] showed that typical processing conditions begin to significantly affect the rheological and mechanical properties of starch-based biodegradable polymers only after five extrusions.
Studies on monopolymer blends [
18,
19,
20,
21] reported that the mechanical and rheological properties of these blends were in most cases intermediate between those of the two components used alone.
Bio-Flex
® is a commercial blend of poly(lactic acid) PLA and poly(butylene adipate-co-terephthalate) (PBAT) [
22] used in various applications. This polymer is biodegradable although not fully bio-based. Due to its physical properties, it is generally considered the biodegradable alternative to low-density polyethylene; moreover, it is one of the new PLA-based materials approved for food contact [
23] and thus commercially available with wide use in food packaging.
In this paper, a sample of commercially available Bio-Flex
® F2110 was reprocessed up to two times using a single-screw extruder. The main purpose was to determine the effect of small amounts of reprocessed polymer on the rheological (shear and elongation) then mechanical properties of monopolymer blends. In addition, experimental values of mechanical properties were compared with theoretical values obtained using an additive model proposed in our work [
24].
The results obtained demonstrate that while multiple extrusions significantly affect the mechanical and rheological properties, the concentration of reprocessed material present in the blends very slightly affect the virgin material. These results indicate that the properties of the monopolymer blends were similar to the virgin material. In addition, the experimentally observed trends were accurately predicted by the additive model.
4. Conclusions
In this study, a commercial biopolymer called Bio-Flex® F2110 was reprocessed in a single extruder up to two times. Then, a fraction was ground and reprocessed, at 10 and 25 wt%, with the same virgin polymer, simulating a classic industrial recycle operation. The mechanical and rheological properties in shear and elongation flow were evaluated. The results obtained showed the predominance of the chain scission mechanism, with the exception of the R225 blend, which appeared to show both chain scission behavior and branching. The mechanical results showed the great recyclability of this polymer system in monopolymer blends, as the rheological and mechanical property values remain almost constant compared to the virgin material. Finally, the additive model adopted predicts the behavior of these monopolymer blends quite well.