Copolyester toughened poly(lactic acid) biodegradable material prepared by in situ formation of polyethylene glycol and citric acid.

Polylactic acid (PLA) is a high-modulus, high-strength bio-based thermoplastic polyester with good biodegradability, which is currently a promising environmentally friendly material. However, its inherent brittleness has hindered its widespread use. In this study, we reported a simple and non-toxic strategy for toughening PLA, using biodegradable materials such as polyethylene glycol (PEG) and citric acid (CA) as precursors. Through reactive melt blending with PLA, PEG and CA form PEGCA copolyesters in situ during blending. At the same time, CA can react with PLA and PEG, forming a copolyester structure at the interface of the two phases, improving the interfacial compatibility between PEG and PEGCA with PLA. Fourier transform infrared spectroscopy confirms this. Experimental results show that when the content of PEG/CA reaches 15% (PLA/PEG/CA-15%) in the blends, the impact strength of the blend was 4.47 kJ m-2, and the maximum elongation at break was as high as 360.1%, which were about 2 and 44 times higher than those of pure PLA, respectively. Moreover, the tensile strength was still maintained at the level of 70%. This work can expand the application of PLA in food packaging and medical supplies.

Protein modified cellulose nanocrystals on reinforcement and self-driven biodegradation of aliphatic polyester.

Due to the highly environment-dependent biodegradation and uncontrolled degradation period, the long-run feasibility and effectiveness of biodegradable polymers are extensively questioned to solve plastics waste accumulation and pollution problems. This work physically incorporated lipase PS from Burkholderia cepacian on cellulose nanocrystals (CNC) and embedded it in polycaprolactone (PCL) to construct stable and controllable interfacial microenvironment between CNC and PCL for the reinforcement and controllable self-driven biodegradation. The physical adsorption of lipase PS on CNC was studied by monitoring the surface charge and particle size. FT-IR spectra confirmed the successful incorporation of lipase PS and CNC. Compared with CNC, protein-modified CNC had a higher maximum thermal decomposition temperature of 345 °C and lower interfacial tension of 11 mN/m with PCL which provided PCL composites with higher nucleation efficiency and tensile elongation of 1086 % at break. In addition, only 0.67 % embedded lipase PS completely hydrolyzed PCL membranes in <140 h. The post-compression molding at 80-100 °C had negligible influence on the lipase activity, which indicated that CNC could protect the lipase from inactivation in polymer extrusion and compression. This work also highlighted protein-modified CNC as a new technology for polymer reinforcement.

A facile strategy for preparation of strong tough poly(lactic acid) foam with a unique microfibrillated bimodal micro/nano cellular structure.

This work reports the design and fabrication of strong tough poly(lactic acid) (PLA) foam by combining pressure-induced-flow (PIF) processing with supercritical CO2 foaming. PIF processing widened the foaming window of PLA to 40-120 °C, while supercritical CO2 foaming released the undesired internal stress of PLA samples with PIF processing (P-PLA). The prepared PLA foams displayed a unique microfibrillated bimodal micro/nano cellular structure which is strongly affected by saturation temperature (Ts). Both micron and nano cells showed decreasing cells size and increasing cell density as Ts elevated. The orientation factor as well as internal stress of PLA foams decreased with increased Ts. Compared with P-PLA samples, PLA foam prepared at Ts of 40 °C showed negligible reduction of orientation from 0.45 to 0.41 and release of internal stress characterized by the rightward shift of Raman peak (stretching vibration of CO bond from 1763 to 1766 cm-1). Furthermore, PLA foam prepared at Ts of 40 °C presented excellent impact strength (32.3 kJ/m2), tensile strength (42.0 MPa), and ductility (14.2%). The combination of PIF processing and supercritical CO2 foaming provides a facile and effective method to prepare strong tough PLA foam that has immense potential in biomedical, aerospace, automotive, and other structural applications.

Synthesis of Transition Metal Complexes and Their Effects on Combustion Properties of Semi-Rigid Polyvinyl Chloride.

Using introduction of MoO42- and Fe3+, Cu2+, or Zn2+ into amphiphilic polymers (DN) via an ion-exchange reaction, different transition metal complexes, as retardants and smoke suppressants, including (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo were synthesized. Combined with the results of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), it could be determined that ionic bonding of these ions with DN occurred. Subsequently, the influence of flame-retardant, smoke-suppression, and mechanical properties of (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo on polyvinyl Chloride (PVC) were tested. It was demonstrated that transition metal complexes of three metal elements, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo, showed better flame retardancy, smoke suppression, and thermal stability as confirmed by microcalorimetry, limiting oxygen index (LOI), smoke density, and thermogravimetric analysis (TGA) tests, in which Cu(DN)Mo worked best due to the Lewis acid mechanism and reductive coupling mechanism. Scanning electron microscopy (SEM) showed that the addition of (DN)Mo, Fe(DN)Mo, Cu(DN)Mo, and Zn(DN)Mo promoted the formation of a dense carbon layer on the PVC surface during combustion, which could protect the interior PVC. The addition of these transition metal complexes hardly impaired the mechanical properties of PVC.

Degradable Controlled Release Fertilizer Composite Prepared via Extrusion: Fabrication, Characterization, and Release Mechanisms.

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate "smart fertilizers" for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the "bottleneck" for nitrogen-phosphorous-potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers.