Designing Sustainable Polymer Blends: Tailoring Mechanical Properties and Degradation Behaviour in PHB/PLA/PCL Blends in a Seawater Environment

Biodegradable polyesters are a popular choice for both packaging and medical device manufacture owing to their ability to break down into harmless components once they have completed their function. However, commonly used polyesters such as poly(hydroxybutyrate) (PHB), poly(lactic acid) (PLA), and polycaprolactone (PCL), while readily available and have a relatively low price compared to other biodegradable polyesters, do not meet the degradation profiles required for many applications. As such, this study aimed to determine if the mechanical and degradation properties of biodegradable polymers could be tailored by blending different polymers. The seawater degradation mechanisms were evaluated, revealing surface erosion and bulk degradation in the blends. The extent of degradation was found to be dependent on the specific chemical composition of the polymer and the blend ratio, with degradation occurring via hydrolytic, enzymatic, oxidative, or physical pathways. PLA presents the highest tensile strength (67 MPa); the addition of PHB and PCL increased the flexibility of the samples; however, the tensile strength reduced to 25.5 and 18 MPa for the blends 30/50/20 and 50/25/25, respectively. Additionally, PCL presented weight loss of up to 10 wt.% and PHB of up to 6 wt.%; the seawater degradation in the blends occurs by bulk and surface erosion. The blending process facilitated the flexibility of the blends, enabling their use in diverse industrial applications such as medical devices and packaging. The proposed methodology produced biodegradable blends with tailored properties within a seawater environment. Additionally, further tests that fully track the biodegradation process should be put in place; incorporating compatibilizers might promote the miscibility of different polymers, improving their mechanical properties and biodegradability.

Physical Properties of Shellac Material Used for Hot Melt Extrusion with Potential Application in the Pharmaceutical Industry

Hot melt extrusion offers an efficient way of increasing the solubility of a poorly soluble drug. Shellac has potential as a pharmaceutical matrix polymer that can be used in this extrusion process, with further advantages for use in enteric drug delivery systems. The rheological property of a material affects the extrusion process conditions. However, the literature does not refer to any published work that investigates the processability of various shellac materials. This work explores various types of shellac and explores their physicochemical and thermal properties along with their processability in the hot melt extrusion application. Physicochemical characterization of the materials was achieved using differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Additional processability characterization was achieved using melt flow index and rheology analysis. The results indicated that there was no chemical difference between the various shellac types compared in this study. However, the extrudable temperature ranges and rheological properties of different shellac types varied; SSB 55 Pharma FL had the lowest processing temperature and glass transition temperatures. Due to the shear-thinning behaviours, shellac can be extruded at lower temperatures. This study provides necessary data to determine the processing conditions in hot melt extrusion applications for the range of shellac materials.

The Influence of Low Shear Microbore Extrusion on the Properties of High Molecular Weight Poly(l-Lactic Acid) for Medical Tubing Applications

Biodegradable polymers play a crucial role in the medical device field, with a broad range of applications such as suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. Poly-l-lactic acid (PLLA) is one of the most commonly used and investigated biodegradable polymers. The objective of this study was to determine the influence low shear microbore extrusion exerts on the properties of high molecular weight PLLA for medical tubing applications. Results showed that even at low shear rates there was a considerable reduction in molecular weight (M_n = 7–18%) during processing, with a further loss (M_n 11%) associated with resin drying. An increase in melt residence time from ~4 mins to ~6 mins, translated into a 12% greater reduction in molecular weight. The degradation mechanism was determined to be thermal and resulted in a ~22-fold increase in residual monomer. The differences in molecular weight between both batches had no effect on the materials thermal or morphological properties. However, it did affect its mechanical properties, with a significant impact on tensile strength and modulus. Interestingly there was no effect on the elongational proprieties of the tubing. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.