When applying electron or gamma irradiation to poly-3-hydroxybutyrate (P3HB), main chain scissions are the dominant material reactions. Though propositions have been made that crosslinking in the amorphous phase of P3HB occurs under irradiation, a conclusive method to achieve controlled additive free irradiation crosslinking has not been shown and no mechanism has been derived to the best of our knowledge. By applying irradiation in a molten state at 195 °C and doses above 200 kGy, we were able to initiate crosslink reactions and achieved gel formation of up to 16%. The gel dose Dgel was determined to be 200 kGy and a range of the G values, the number of scissions and crosslinks for 100 eV energy deposition, is given. Rheology measurements, as well as size exclusion chromatography (SEC), showed indications for branching at doses from 100 to 250 kGy. Thermal analysis showed the development of a bimodal peak with a decrease in the peak melt temperature and an increase in peak width. In combination with an increase in the thermal degradation temperature for a dose of 200 kGy compared to 100 kGy, thermal analysis also showed phenomena attributed to branching and crosslinking.

Bioplastics research is currently challenged by high material prices and limited availability of biopolymers. For state-of-the-art compounding using a twin-screw extruder, even on lab-scale, large quantities of material are required. Poly(3-hydroxy-buthyrate) and its copolymers such as PHBV are promising biopolymers but are prone to degradation. The stabilizers used must also be biobased to ensure the sustainability of the material. In this study, a new material-saving process for the compounding of biocomposites was evaluated to investigate the potential of biogenic by-products from the winemaking industry to improve the stability of biopolyesters. Formulations based on PHBV powder and two different varieties of pulverized wine grape pomace with filler contents up to 10 wt.-% were prepared. The materials were processed on a modified miniaturized single-screw extruder with an L/D ratio of 15 equipped with a mixing screw and compared to a lab-scale twin-screw extruder with an L/D ratio of 44. Both extruders have screw diameters of 20 mm. Thermal and rheological properties of the compounded material were determined using standard polymer analyzing techniques such as GPC, MFR, DSC, TGA and OIT. The mixing quality of both extruder types was evaluated by light microscopy imaging. The results show that a miniaturized single-screw extruder represents an efficient alternative for research purposes, but minor differences in the dominant degradation mechanisms during processing must be considered for data evaluation. Especially for small quantities and frequent material changes, the miniaturized single-screw extruder is a beneficial option, reducing the limits of bioplastics research and contributing to its progress. Thermal analysis revealed that the wine-derived biogenic by-products act as antioxidant stabilizers preventing thermo-oxidative degradation of PHBV, representing sustainable biobased alternatives to synthetic stabilizers.

Bio-based polyamide 10.10 (PA 10.10) has excellent properties compared to other biobased  polymers such as polylactic acid (PLA) or polyhydroxyalkanoates (PHAs) and is therefore used in more technical applications where higher strength is required. For foam and filament extrusion,a good balance between strength and stiffness of the  polymer is needed. Therefore, two commercial chain-extenders (Joncryl® ADR types) with different epoxy functionalities are used to modify the melt properties of PA 10.10. The chain-extenders are used in a concentration range up to 1.25 wt.%. The range of glass transition temperature widens with increasing Joncryl® content, and the apparent activation energy shows a maximum at a concentration of 0.5 wt.%. Furthermore, the melting temperatures are constant and the crystallinity decreases with increasing chain-extender content due to the formation of branches. During the second heating run, a bimodal melting peak appeared, consisting of 𝛼-triclinic and pseudo 𝛾-hexagonal crystals. The weight average molar masses (Mw) measured by gel permeation chromatography (GPC) increased linearly with increasing ADR 4400 content. In contrast, the compounds containing ADR 4468 show a maximum at 0.5 wt.% and it begins to decrease thereafter. The rheological data show an increase in viscosity with increasing chainextender content due to branch formation. ATR spectra of the compounds show a decrease at the wavelength of the primary (3301 cm−1) and secondary (1634 cm−1) (-NH stretching in PA 10.10) amine, indicating that chain-extension, e.g., branching, takes place during compounding.

Biobased poly(butylene succinate) (PBS) represents one promising sustainable alternative to petroleum-based polymers. Its sensitivity to thermo-oxidative degradation is one reason for its limited application. In this research, two different varieties of wine grape pomaces (WPs) were investigated as fully biobased stabilizers. WPs were prepared via simultaneous drying and grinding to be used as bio-additives or functional fillers at higher filling rates. The by-products were characterized in terms of composition and relative moisture, in addition to particle size distribution analysis, TGA, and assays to determine the total phenolic content and the antioxidant activity. Biobased PBS was processed with a twin-screw compounder with WP contents up to 20 wt.-%. The thermal and mechanical properties of the compounds were investigated with DSC, TGA, and tensile tests using injection-molded specimens. The thermo-oxidative stability was determined using dynamic OIT and oxidative TGA measurements. While the characteristic thermal properties of the materials remained almost unchanged, the mechanical properties were altered within expected ranges. The analysis of the thermo-oxidative stability revealed WP as an efficient stabilizer for biobased PBS. This research shows that WP, as a low-cost and biobased stabilizer, improves the thermo-oxidative stability of biobased PBS while maintaining its key properties for processing and technical applications.

Linear low-density polyethylene (LLDPE) crosslinks under irradiation in the range of up to 250 kGy. Crosslinking leads to better chemical and thermal resistance but causes reduction in mechanical performance. To counter this reduction, compounds of LLDPE with thermoplastic elastomers (TPV) were made. Specimens were irradiated with doses reaching from 99 to 231 kGy. Gel content shows a decrease of around 12% for compounds with 20 wt% of TPV compared to pure LLDPE. It is also found that compounds containing 10 wt% TPV experience a 4% higher gel content than predicted. For higher amounts of TPV elongation at break increases from 689% for pure LLDPE to 769% and tensile strength decreases from 31.9 to 30.5 MPa. Under irradiation, a trend to lower elongations and tensile strengths is observed. Elongation at break decreased around 200% and tensile strength around 5 MPa under irradiation. Thermal analysis of TPV showed that while the melting temperature decreases, its crystallinity first rises for doses up to 165 kGy before decreasing. Infrared spectroscopy was used to identify changes in the chemical structure, where evidence of surface oxidation under irradiation is found for all compounds with LLDPE.