Influence of recycling of poly(lactic acid) on packaging relevant properties

Abstract

The most promising representative of biodegradable plastics in packaging applications is polylactide (PLA). Despite this, there is only a small market of PLA in Europe. Reasons for that are the high price of PLA raw material and the lack of knowledge of the behavior in packaging applications. It has a number of peculiarities so producers of plastics packaging hesitate to use it. Like other polyesters, it can degrade at increased temperatures in the presence of moisture by hydrolysis whereby it loses its physical and chemical properties. In all production processes, production waste is generated (i.e., stamping grids or edge trim). In most cases, this waste is used. It is not known in detail, how an internal recycling process will influence the final product properties. One problem is hydrolysis by which the production waste is partially degraded. Target of this study is to analyze the recycling process of PLA within the context of necessary process adaptions and the effects upon ecological efficiency. Films for packaging containing multiple types and amounts of production waste will be produced by extrusion and tested concerning their mechanical properties. The analysis of the recycling behavior showed that internal PLA production waste is well suitable for recycling. The influence of the recycling on the molecular weight is negligible. The effect on the viscosity and thus on the extrusion process is higher. Packaging relevant properties like mechanical or optical properties are hardly influenced. Especially recycling with a recycling quota of up to 50% has an insignificant effect on the film properties.

Long-term properties and end-of-life of polymers from renewable resources

“…The mechanical recycling of PLA has been approached in lab-scale studies by means of multiple injection [183], [275]- [277] and extrusion [278]- [281] steps, and the recyclates characterized in terms of structural and morphological analysis rheological, thermal and mechanical properties, release of low molecular weight compounds (LMWC) [282], and application-driven techniques such as mass-transport [221] or dielectric properties [181]. A review devoted to the mechanical recycling of PLA [261] showed that, in general terms, reprocessing of PLA was responsible for a decrease in molecular weight, modification of thermal properties and crystallization kinetics, dynamic fragility or permeation performance, among other parameters [261].…”

“…This is the case of the application of physical treatments such as annealing to increase young modulus and yield strength of PLA [275], [283] or the use of chemical stabilizers such as tropolone, quinones or irgafos/irganox during processing to prevent transesterification [284], [285]. Other options include the blending of recycled polymers with other ones that can act as plasticizers or tougheners (blendingin) [277], [286]- [288], or the use of recycled bioplastics as value-added modifiers for other plastic matrixes (blendingout) [289]- [291]. The case of the combination of PLA and PHBV is remarkable [272].…”

Mechanical recycling of polylactide, upgrading trends and combination of valorization techniques

“…aiming durability. Techniques for the analysis of mass-transport properties for the use of recyclates as packaging [44] or concerning dielectric properties [39], [45], [46] are used, among others. On the other side, when the application is to find the most sustainable discarding process for wastes, the combination of further simulations of waste management options [13] such as composting [47], [48] or energetic valorization [20], [42], [49]- [51], among others, have been reported.…”

“…Mechanical recycling of biopolymers has been mainly reported for poly(hydroxybutirate) [60], poly(caprolactone) [61] and polylactide. The mechanical recycling of polylactide has been approached in lab-scale studies by means of multiple injection [35], [62] and extrusion [44], [63], [64] steps, during one [65], three [64], five , [66] and ten [63] processing cycles, and the recyclates characterized in terms of structural and morphological analysis [35], [62], [65], rheological, thermal and mechanical…”

“…In this line, a pilot project was started in PLA recycling by yogurt maker Stonyfield Farm, which began working with NatureWorks on mechanical recycling of PLA trim scrap from its thermoforming/filling/sealing packaging lines [105]. Other studies have pointed out the potential of internal recycling up to a recycling quota of 50%, maintaining the mechanical and optical properties, with little influence on the molar mass [44].…”