Degradation of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Reinforced with Regenerated Cellulose Fibers.

PHBV is a promising plastic for replacing conventional petroleum-based plastics in the future. However, the mechanical properties of PHBV are too low for use in high-stress applications and the degradation of the polymer limits possible applications. In this work, the mechanical properties were, therefore, increased using bio-based regenerated cellulose fibers and degradation processes of the PHBV-RCF composites were detected in accelerated aging tests under various environmental conditions. Mechanical, optical, rheological and thermal analysis methods were used for this characterization. The fibers significantly increased the mechanical properties, in particular the impact strength. Different degradation mechanisms were identified. UV radiation caused the test specimens to fade significantly, but no reduction in mechanical properties was observed. After storage in water and in aqueous solutions, the mechanical properties of the compounds were significantly reduced. The reason for this was assumed to be hydrolytic degradation catalyzed by higher temperatures. The hydrolytic degradation of PHBV was mainly caused by erosion from the test specimen surface. By exposing the regenerated cellulose fibers, this effect could now also be visually verified. For the use of regenerated cellulose fiber-reinforced PHBV in more durable applications, the aging mechanisms that occur must be prevented in the future through the use of stabilizers.

Tuning of cellulose fibres' structure and surface topography: Influence of swelling and various drying procedures.

Presented study deals with the pre-treatment of cellulose fibres with the aim to activate their surface and to enlarge their pore system, leading to an enhancement of fibres' affinity for subsequent functionalization processes. Swelling of fibres in aqueous solutions of sodium hydroxide opens their fibrillar structure, while freezing and freeze-drying retain this enlargement of the pore system, in contrast with conventional air or elevated temperature drying. Effect of different pre-treatment procedures on fibres' supramolecular structure, enlargement of their pore system, surface topography, zeta potential and mechanical properties was investigated. Degree of enhancement of the pore system depends on the concentration of sodium hydroxide and type of freezing; higher alkali concentrations are more effective, but at the cost of extensive deterioration of mechanical properties. Swelling of fibres in lower concentrations of NaOH, in combination with freeze drying, offers an acceptable compromise between enhancement of the fibres' pore system, changes in surface potential and tensile properties of treated fibres. Design of a suitable regime of swelling and drying of cellulose fibres results in an effective procedure for controlled tuning of their surface topography in combination with an increase of the available internal surface area and pore volume.