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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.

A process for preparing emulsions of alkyl ketene dimer (AKD) nanoparticles

Curable precursors for production of thermosetting (co)polyesters are developed based on poly(butylene adipate) (PBA), poly(ethylene terephthalate), and poly(lactic acid) (PLA). The precursors are prepared from methacrylation of their hydroxyl-terminated oligomers. These include commercial HO-capped PBA prepolymer (HO-PBA), and bis-2-hydroxyethyl terephthalate (BHET) and glycolized PLA (GPLA), which are obtained from glycolysis reactions of their post-consumer products and original resin. The optimal conditions for methacrylation of each prepolymer, i.e., molar ratios of prepolymer to methacrylic anhydride (MAAH), temperature and time, are examined. The most efficient conditions are 1:4/120 °C/3 h (HO-PBA), 1:2.5/120 °C/2 h (BHET), and 1:4/140 °C/3 h (GPLA), respectively. These conditions are justified, where the highest degree of substitution and double bond content are obtained without self-curing side reaction. The resulting methacrylated precursors from HO-PBA and BHET are isothermally cured faster than those of GPLA. Thermosetting copolyesters developed from binary mixtures of the precursors possess tunable thermal stability, and physical and mechanical properties. The degradable copolyesters can be applied in various applications, especially in packaging and agricultural fields.

A process for the chemical recycling of degradable polylactide (PLA) has been developed, to convert its disposable wastes into small-sized products for further use as value-added starting materials for specialty products. A microwave-assisted alcoholysis reaction, using diols and tetrabutyl orthotitanate (TBT) catalyst, was employed. The effects of the types of diols and PLA/diol feeding ratios on the structures and properties of the resulting alcoholized products were examined by using ethylene glycol (EG), propane-1,3-diol (PDO), and butane-1,4-diol (BDO). The PLA/diol ratios were varied from 1:1 to 4:1 wt/wt. The products were characterized by ATR-FTIR, 1H NMR, and 2D-NMR HMQC and HMBC spectroscopy. The products compost to diol-capped lactate sequences with different lengths, i.e., lactate, lactyllactate, and poly-lactate. The yield of the shortest lactate was about 65% for the LBDOT11 system, and 90% for the LEGT11 and LPDOT11 systems, when a feeding ratio of 1:1 wt/wt was employed. The yield decreased with an increase in the ratios, from 1:1 to 4:1 wt/wt. In contrast, the yields of longer lactyllactate and poly-lactate increased with an increase in the ratios. In terms of OH-endcapping efficiency, the products have two structures: (A) LA-O-(CH2)x-OH and (B) LA-O-(CH2)x-O-LA. The contents depend on diol types and the PLA/diol feeding ratio. The alcoholized products were then used as starting polyols in the preparation of lactide-based polyurethanes (PUs) by reacting with 1,6-diisocyanatohexane (HDI) and BDO chain extender. The resulting PUs exhibit promising mechanical and thermal properties. These PUs are suitable for use as either single-component materials, e.g., 3D-printing filaments and degradable adhesives, or as toughness-enhancing agents for brittle polymers, especially PLA.

Hydroxyl-capped polylactic acid (PLA) oligomers are prepared by glycolysis reaction of PLA with ethylene glycol (EG) and used as a macromolecular cross-linker for epoxidized natural rubber (ENR). The glycolyzed PLA (GPLA) with three different molecular weights (2000, 10,000, and 44,000 g mol−1) are prepared by varying the glycolysis conditions. Effects of GPLA chain lengths and GPLA/ENR feed ratios on cross-linking efficiency, chemical structures, and physical properties of the cured products are investigated. The cross-linking efficiency is examined using a moving die rheometer, solvent fractionation, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Optimum GPLA/ENR compositions for the curing reaction range from 20 wt% to 33 wt%, depending on the GPLA chain length. Because of their biodegradability, biocompatibility, and the ability to tune up their structures and properties, the cured rubber materials have high potential for use in various biomedical applications.

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.

Glycolyzed polylactic acid (GPLA)-cured epoxidized natural rubber (ENR) is developed for use as a toughening agent for PLA resin. GPLA is obtained from chemical recycling of PLA resin by a glycolysis reaction. GPLA-cured ENR is then prepared by the crosslinking reaction of ENR with GPLA in an internal mixer. Chemical structures of the cured products are characterized by solvent fractionation and thermogravimetric analysis (TGA). The cured ENR products are blended with PLA resin, by varying the cured ENR contents from 5 to 15% wt. Mechanical properties of the blends, and their toughening mechanisms are examined. The cured ENR materials has higher efficiency in improving toughness of PLA resin, compared to uncured ENR, likely due to their rubbery network nature and higher compatibility with the PLA matrix. The incorporation of 5% wt. GPLA-cured ENR also improves elongation at break with no adverse effect on tensile strength and modulus of PLA.

The reductions of silver nitrate by tannic acid at various pH with and without UV radiation at room temperature were done in order to study the effects of UV radiation and pH of tannic acid solution in the synthesis of silver nanoparticles. The results from UV-Visible spectroscopy, dynamic light scattering method and transmission electron microscopy indicated that using UV radiation resulted in silver nanoparticles with smaller particles and narrower size distribution at every pH. The results also revealed that smallest particles without agglomeration were obtained when alkali condition was applied. Therefore, the suitable condition for synthesizing silver nanoparticles in this research was to use UV radiation and tannic acid solution having pH of 8.0.

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

Curable precursors are prepared from chemical recycling of degradable polylactic acid (PLA) for development of aliphatic polyester thermoset materials. PLA resin (NatureWork 4042D) was de-polymerized via glycolysis under various conditions to produce PLA glycolysates (GlyPLAs), whose chain-ends mainly consist of hydroxyl groups with $$\bar{M}_{n}$$ ranging from 3,600 to 17,000 g/mol. Unsaturated double bonds (DB) were introduced into GlyPLA structures by end-capping with methacrylic anhydride to generate curable LA-precursors. The end-capping efficiency is strongly dependent on the molecular weight of GlyPLAs, where smaller-sized glycolysates produce LA-precursors with higher DB content. Curing behaviors of the precursors are thoroughly examined. DSC and FTIR results show that curing reactions at 140 °C are completed after 2 h for all samples. Results on gel fraction indicate that LA-precursor with $$\bar{M}_{n}$$ ~ 3,600 g/mol is the most effective candidate for producing network products with high crosslink density.

Aliphatic/aromatic copolyesters, which possess good mechanical property and degradability, are of immense interest. Standard characterization techniques for the copolymer structure and degradation behaviors have been developed. The techniques are applied to examine hydrolytic degradation of poly(ethylene terephthalate- co -lactic acid) in a phosphate buffer solution (pH 7.2) at 60 °C. The weight loss of the copolymer and pH of the medium as a function of time are examined. 1 H NMR spectra provide information on microstructure and molecular weight of the samples, where deviations of the results from the actual values are observed, due to low solubility of the copolymer. More accurate results are obtained from TGA and FTIR experiments, as the samples are characterized in bulk. Insight into degradation mechanisms of the copolymer is derived from FTIR spectra. The content of aromatic esters in the soluble degraded species is determined from UV–Vis spectroscopy. These standard methods can be applied to various types of degradable aliphatic/aromatic copolyesters, which are essential in property assessment and determination of their potential applications.

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.

Poly(L)lactide (PLLA), aliphatic polyester, and poly(LLA-co-DLLA) copolymers consisting of 2.5, 7.5, 50% of DLLA content were also synthesized. PLLA was successfully electrospun by using 15wt% solution in (1DMF:3CHCl3) mixed solvent. 2.5, 7.5, 50% P(LLA-co-DLLA) copolymers were then spun at 8, 10, and 15wt% concentration in a single chloroform solvent, respective. The lactide-based polymeric nanofibers were characterized by Scanning Electron Microscope (SEM). Smooth surface morphology was observed in nanofibers produced from PLLA and 50% P(LLA-co-DLLA) copolymer. However, surface porosity was observed in the corresponding fibers from 2.5 and 7.5% P(LLA-co-DLLA) copolymers. These nanofibers have high potential for wide range of applications such as filter media, nano-sensor, drug delivery and tissue scaffold, especially, those derived from 2.5 and 7.5% P(LLA-co-DLLA) copolymers which contain high degree of porosity.

Poly(lactic acid-co-ethylene glycol) (PLLA/PEG) copolymers were synthesized and their properties were characterized. The PLLA/PEG/PLLA triblock copolymers were synthesized by ring-opening polymerization from l-lactide (LLA) and PEG macroinitiator. Stannous octoate, Sn(Oct)2 was used as a catalyst. Effects of molecular weight of PEG (600, 2000 and 4000), LLA/OH molar ratios (95:5, 98:2) and a sequence of addition of the reactants on properties of the copolymers were investigated. The triblock copolymers were subsequently used in a production of multiblock copolymers by reacting with a chain-extending agent, hexamethylene diisocyanate (HMDI). Chemical structure and molecular weight of the copolymers were characterized by 1H-NMR, FTIR and GPC. The results showed that molecular weight of triblock copolymers varied from 4,500 to 10,200. After chain extension, multiblock copolymer with molecular weight of 16,490 was produced. Thermal properties of the copolymers were also examined by DSC.

Inter- and intramolecular crosslinking is the main cause of the water insolubility of phosphorylated chitosan synthesized with a phosphorus pentoxide/methanesulfonic acid system. The goal of this study was to eliminate inter- and intramolecular crosslinks and synthesize water-soluble phosphorylated chitosan. Two main factors for the formation of inter- and intramolecular crosslinks are (i) electrostatic interaction between amino groups and methanesulfonic acid salt and (ii) electrostatic interaction between ammonium groups and phosphoric groups. The influences of ethanol washing and sodium salt formation on the elimination of inter- and intramolecular crosslinks were investigated. Sodium phosphorylated chitosan was water soluble. The solubility was independent of the degree of phosphoric substitution.

In this study, effects of saturated acids on physical properties, including hardness, impact strength, flexural properties and thermal properties, of unsaturated polyester or UPE resins prepared from recycled PET bottles and fabrics were investigated. PET was depolymerized by glycolysis reaction with the excess propylene glycol in the presence of zinc acetate as a catalyst. UPE resins were then synthesized by polyesterification of these glycolyzed products with maleic anhydride as an unsaturated diacid as well as succinic acid and adipic acid as a saturated diacid. With the addition of styrene monomer, UPEs were subsequently casted into specimens by crosslinking reaction using methyl ethyl ketone peroxide and cobalt octoate as an initiator and a catalyst, respectively. Physical properties of the cured specimens were then studied. The results showed that, when a saturated acid was incorporated, the hardness of the cured UPE resins decreased due to the decreasing amount of crosslinks. The extended distance between crosslinking sites on molecular chains facilitated load distribution, resulting in the significant improvement of impact strength. The flexural strength was also improved when the small amount of saturated acid was used. The onset thermal degradation temperatures and the glass transition temperatures of the prepared UPE resins were almost unchanged.

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.

Urea fertilizer is a major source of nitrogen, which is one of the essential nutrients for plant growth. Due to its uncontrollable release, this chemical can be wasted easily by leaching and volatilization that can adversely cause the contamination to the environment. In this work, a controlled-release material for urea fertilizer has been prepared by using degradable polylactic acid. Unlike other conventional controlled-release system, the resulting material is able to provide an efficient supply of urea fertilizer, without causing further contamination to the environment from residue material, as polylactic acid can be degraded in the environment. Micron-size particles of polylactic acid coated urea were prepared by employing atomizing technique. Effect of the preparation conditions; urea/PLA composition, PLA concentration, and pressure of atomizing gun on the particle size of material are investigated. The urea release rate of these samples is then studied by employing UV-Visible spectrophotometer. In addition, the effect of preparation conditions on shape and morphology of sample is determined by using Scanning Electron Microscope (SEM).

PLA-based aliphatic aromatic copolyesters have been synthesized and characterized in order to incorporate the degradability of PLA and good mechanical properties of aromatic species. Synthesis of the copolymers was conducted by polycondensation of lactic acid with dimethyl terephthalate (DMT) and various diols using stannous(II) octoate as a catalyst. Three types of diols with different methylene lengths were employed, i.e., ethylene glycol (EG), propylene glycol (PG) and 1, 4-butanediol (BD). Effects of diols and comonomer molar ratio on the extent of polycondensation reaction and molecular weight of the resulting copolymers were investigated. Diacids and diol ratios of L-lactic acid (LLA), dimethyl terephthalate (DMT) and diol of 1/1/2, 1/2/4 and 2/1/2 were employed. Characterization of chemical structure, molecular weight and thermal and physical properties of the resulting copolymers were conducted by FTIR, NMR, and DSC.

ontrolled-release materials for urea are prepared by spray coating urea granulates with lactic acid based homo- and co-polymers solutions. Percent coating as a function of polymer types, molecular weight, polymer concentration, and dose applications are examined by gravimetric analysis. Percentage of urea dissolution in water of the coated fertilizer is measured by monitoring refractive index of the solutions. Morphology of the polymer coating surfaces is revealed by Scanning Electron Microscopy (SEM). It was found that an amount of cracks and pin-holes, which is dependent on polymer types and molecular weight, plays a significant role in controlling the rate of urea release. Results from urea dissolution test also suggests that the synthesized poly(lactic acid-co-ethylene terephthalate) show urea-holding efficiency comparable to that of commercial PLA, despite its much lower molecular weight, indicating that the copolymer is potentially suitable for this specific application.

Because of their respective advantages, the combination of good material properties of poly(ethylene terephthalate) (PET) and degradability of polylactic acid (PLA) is researched as degradable copolymer for packaging and agricultural applications. Poly(ethylene terephthalate-co-lactic acid) (PET-co-PLA) has been synthesized by employing polycondensation of mixtures of dimethyl terephthalate (DMT), lactic acid (LA) and ethylene glycol (EG), using tin(II) octoate as a catalyst. A chain-extending reagent, hexamethylene diisocyanate (HMDI), was then used in the subsequent step to increase the chain length of the copolymer and improve its mechanical properties for suitable applications. The chemical structure and molecular weight of the copolymers were investigated by FTIR, NMR, and DSC. NMR results indicated the incorporation of lactic acid and PET units in the copolymer chain. Additionally, blends of the resulting copolymer with commercially-available PLA were studied. The blend miscibility was examined by DSC and FTIR spectroscopy.

Thermal properties and crystallization behaviors of polylactide and its enantiomeric blends are investigated. DSC results demonstrate that only homopolymer crystallite is observed in PDLA and PLLA single polymers. A relatively stronger crystal structure, stereocomplex, can be achieved by mixing the two PLAs in a 1:1 ratio. For non-equimolar blends, both types of crystallites are formed at lower temperature than that of the single polymer counterparts. The degree of reduction in crystallization temperature is dependent on the degree of deviation of blend content from the equimolar value and the mobility of the polymer chain. The composition of the two crystallite domains is also dependent on the blend content, where the stereocomplex content is maximized in a 1:1 blend, and decreases upon varying the mixing ratio from equimolar value. Infrared spectroscopy is employed to follow the crystallization mechanisms of the non-equimolar blend. Results indicate a domination of stereocomplex formation band characteristics, despite evidences suggesting an existent of homopolymer crystallite formation, probably due to the involvement of C-H..O=C hydrogen bonding, which leads to larger change in dipole moment responsible for infrared transitions.

The band origins and transitions of weak vibrational modes developed in the 3500 cm−1 region of polylactide (PLA) spectra during crystallization are investigated. The band assignment to the OH stretching mode of terminal hydroxyls is unlikely because the trace amount of chain-ends is negligible considering the long chain of high molecular weight polymer. The band intensity can be enhanced for quantitative study by increasing the sample film thickness. The results show that the transition patterns of these bands mimic those of C=O stretching modes. Therefore, these are assigned to CXO overtones. Two bands associated with crystalline and amorphous characteristics are revealed during cold crystallization. The crystalline C=O bands of PDLA and its stereocomplex counterpart are located at 3510 cm−1 and 3482 cm−1, respectively, indicating a weaker C=O bond in the latter crystal structure. Two-dimensional Fourier transform infrared (2D-FT-IR) correlation spectroscopy is then applied to study the correlation between C=O overtones and the crystalline characteristic band located near 900 cm−1. The transitions of the two vibrational modes observed in crystallization of the stereocomplex are in-phase with each other. This reflects an involvement of short-range hydrogen bonding in the stereocomplex crystal structure. In contrast, crystallization of PDLA shows that the C=O overtone varies prior to that of the C–H character, indicating that dipole–dipole force is a crystal-induced interaction.