Search

A process for sizing down and functionalizing commercial polylactide (PLA) resin is developed by alcoholysis with 1,4-butanediol (BDO) and propylene glycol (PG) to medium-sized PLA-based diols, with lower cost than a bottom-up synthesis process. These are subsequently used as polyols in preparing polyurethanes (PU) by reacting with 1,6-diisocyanatohexane (HDI). The PLA-based PU has an excellent elongation at break of 487%. The products are suitable as toughening agents for brittle PLA resin due to their highly elastic properties and high compatibility with PLA. The PU products are blended with PLA resin at various compositions, and their physical and mechanical properties and shape recovery are examined. The tensile tests showed enhancements in elongation at break up to 160% with low modulus. The fracture morphology and FTIR results confirm that the blends show strong interfacial interaction and adhesion between the PLA-based PU disperse phase and the PLA matrix. The PLA/PU blends exhibit a high shape recovery efficiency, and their recovery mechanisms are identified. These flexible PLA/PU blends are promising for various applications where bio-compatibility/degradability and high ductility are required, especially as filaments for 3D bio-printing.

Multi-branched poly(D-lactide)s (mbPDLAs) with various structures are synthesized via ring-opening polymer- ization by using polyglycidol (PG) macro-initiators. Their chemical structures and thermal properties are controlled by adjusting feed ratios of D-lactide (DLA) and PG. The materials are blended with commercial linear poly(L-lactide) (l-PLLA) to form a stereocomplex structure. Effects of mbPDLAs structures and l-PLLA/mbPDLA ratios on the blends' thermal, mechanical, and rheological properties are evaluated. Mechanical properties of the stereocomplex blends, espe- cially elongation at break and toughness, are dependent on the blend compositions, in which a 90:10 ratio exhibits the most desirable properties. The material also exhibits the lowest complex viscosity, which provides easy processing conditions. This is achieved by the incorporation of copolymers with multi-branched structures and an ability to form a much stronger stereocomplex structure.

Nanofibers of poly(L-lactide-co-DL-Lactide) (PDLLAx) copolymers with DL-lactate (DLLA) contents of 0, 2.5, 7.5, and 50%, which exhibit strong structure/properties correlation, were fabricated by electrospinning. Effect of the copolymer structure and electrospinning conditions on morphology and properties of the fibers were examined by SEM, DSC, XRD, and tensile measurements. Bead-free fibers of PDLLAx prepared from a DMF/CHCl3 mixed solvent are roughly 10-times smaller in size (600–800 nm), with lower degree of surface porosity, compared to those of CHCl3. When CHCl3 is employed, an increase in size (2.4–5.5 μm) and surface porosity (0–45%) with relative humidity value is observed in crystallizable copolymers, whereas an amorphous copolymer shows a reverse trend. Thermal properties and chain arrangements of the electrospun fibers are critically affected by DLLA content of the copolymers and electrospinning conditions, as a result from interplay between intermolecular and intramolecular hydrogen bonding. Contents of crystalline domains and “physical crosslinks” generated from DL lactate segments are proposed as the origin of this phenomenon. Fiber mats of PDLLA with 50% DLLA content show a large improvement in all aspects of mechanical properties, which are suitable for various biomedical applications. POLYM. ENG. SCI., 54:472–480, 2014. © 2013 Society of Plastics Engineers

Crosslinkable poly(lactic acid-co-glycidyl methacrylate), P(LLA-co-GMA), copolymer was systematically synthesized by ring-opening polymerization. Synthesis parameters, i.e., catalyst type, comonomer ratio and polymerization time and temperature were studied. The incorporated GMA content strongly affected the physical and thermal properties of the obtained copolymers, which varied from semi-crystalline to completely amorphous polymers. Melting and glass transition temperatures, and molecular weights of the copolymers decreased as the GMA content in the copolymer increased. Curing behavior of the copolymers was assessed by employing thermo- and photo-crosslinking processes, and the crosslink density was evaluated via their gel content and solvent swelling ratio. A photo-crosslinking process was proven as a practical method in the curing of the copolymers, as the reaction was almost complete within 2 min, as indicated by a gel content of 96%. In the thermo-crosslinking process, at least a 15-min curing time was required at 120 °C. The cured products of copolymers with 19.2 mol% GMA showed the highest compressive stress at 25.5 MPa. Random copolymer of poly(lactic acid-co-glycidyl methacrylate), P(LLA-co-GMA) was systematically synthesized by ring-opening polymerization. Synthesis parameters, that is, catalyst type, comonomer ratio and polymerization time and temperature were studied. The incorporated GMA content strongly affected physical and thermal properties of the obtained copolymers, which varied from semi-crystalline to completely amorphous polymer. Curing behaviors of the copolymers were assessed by employing thermo- and photo-crosslinking processes, where the crosslink density was evaluated via their gel content and solvent swelling ratio.

A series of 0–3 composites of lead zirconate titanate (PZT)/ferroelectric odd–odd nylons was prepared with variations in the size of PZT powder and in the dipole density of ferroelectric odd–odd nylons. The as-formed PZT powder prepared by a spray-drying technique consists of spherical granules composed of large numbers of interconnected fine particles. Electrical properties of the composites as a function of the size of this particular PZT powder and the dipole density of ferroelectric odd–odd nylons were studied. With the PZT powder sintered at 1100°C, the relative permittivity, polarization, and piezoelectric strain coefficient (d33) of the PZT/nylon composites increased with increasing powder size of PZT. The electrical properties of the composites also increased as the dipole density of the polymer increased. The PZT/nylon 57 composite exhibited a high-relative permittivity and piezoelectric strain coefficient d33 due to an increase in its dipole density. The optimum relative permittivity and polarization of this composite were obtained by the PZT with an average granule size of 95 μm. The highest piezoelectric strain coefficient d33 of the 0–3 composite was found at 28 pC/N whereas the relative permittivity was approximately 73.

Lactic acid-based aliphatic/aromatic copolyesters are synthesized to incorporate the degradability of polylactic acid and good mechanical properties of aromatic species by using polycondensation of lactic acid (LA), dimethyl terephtha- late (DMT), and various diols. Effects of diol lengths and comonomer feed ratios on structure and properties of the result- ing copolymers are investigated. Three types of diols with different methylene lengths are employed, i.e., ethylene glycol (EG), 1,3-propanediol (PD) and 1,4-butanediol (BD). LA/DMT/diol feed ratios of 2:1:2, 1:1:2, and 1:2:4 are used in each diol system. It is found that types of the diols play an important role in the properties of the copolyester, where an increase in diol length results in an increase in the copolymers molecular weight, and a decrease in Tg, Tm and crystallinity, when a constant monomer feed ratio is employed. Monomer feed ratio also has a significant effect on properties of the copolymers, where an increase in the aromatic content leads to formation of copolymers with higher molecular weight, longer aromatic block sequence and high aromatic to aliphatic ratio in the chain structure. These, in turn, lead to an increase in Tg, Tm, crys- tallinity and thermal stability of the copolymer samples, and a reduction in their solubility.

Lactic acid/ethylene terephthalate copolyesters were synthesized by the standard melt polycondensation of lactic acid (L), ethylene glycol (EG) and dimethyl-terephthalate (DMT). Effects of reaction temperatures and types of catalysts on the structures and properties of the copolymers were examined. In addition, feasibility of promoting the copolymerization process by a novel synthesis step of using thermo-stabilizers was investigated. The results show that a reaction temperature of higher than 180°C is necessary to produce copolymers with appreciable molecular weight. However, degradation was observed when the reaction temperature is higher than 220°C. Triphenyl phosphate (TPP) shows promising results as a potential thermo-stabilizer to minimize this problem. It was found that Sb2O3 and Tin(II) octoate are most effective among 4 types of catalysts employed in this study. 1H-NMR results indicate that copolymers have a random microstructure com- posed mainly of single L units alternately linked with ET blocks at various sequential lengths. The longer ET sequence in the chain structure leads to the increase in melting temperature of the copolymer. TGA results show that the resulting copolymers possessed greater thermal stability than commercially-available aliphatic PLA, as a result of the inclusion of T (terephthalate) units in the chain structure.