Polymer Degradation and Stability (v.95, #8)
Editorial by K. Sudesh; H. Abe; T. Iwata (1275).
Biomass carbon ratio of polymer composites included biomass or petroleum origin resources by Toru Onishi; Fumi Ninomiya; Masao Kunioka; Masahiro Funabashi; Keiichi Ohara (1276-1283).
The biomass carbon ratios of various polymer composites were studied. The biomass carbon ratios of polymer composites were estimated by the ratios of 14C to 12C measured by accelerator mass spectrometry (AMS) based on ASTM D 6866-08. The pretreatment conditions of the polymer composite of each constituent for the AMS measurement are described. The repeatability and accuracy of the biomass carbon ratio evaluation by AMS for the polymer composites with an inorganic filler, which are biomass-based plastics with mineral calcium carbonate and petroleum-based plastics with biobased calcium carbonate, such as shell powder or an organic filler, are discussed. The standard deviation of the polymer composite was less than 1%, and it was sufficiently lower compared with the limit of the AMS measurement (0.12%). Also, the biomass carbon ratio of each constituent of the polymer composite including the inorganic filler was significant based on the AMS measurement by changing the pretreatment conditions.
Keywords: Polymer composite; Calcium carbonate; Cellulose; Biomass carbon ratio; Accelerator mass spectrometry; Repeatability;
Effect of ethylene glycol on the end group structure of poly(3-hydroxybutyrate) by Kenji Yamanaka; Yoshiharu Kimura; Takashi Aoki; Toshiji Kudo (1284-1291).
Ralstonia eutropha was cultivated in a culture medium supplemented with ethylene glycol (EG), which is known to act as a chain transfer agent in the production of poly(3-hydroxybutyrate) (PHB). The PHB extracted from the bacterial cells was analyzed by 1H and 31P NMR spectroscopies and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The addition of EG exerted a remarkable influence on the mass of production and molecular weight of PHB, and then was found to result in chain transfer and termination reactions. MALDI-TOF MS of the partially hydrolyzed PHB revealed that either succinate or glutarate combined with the hydroxyl terminals of PHB as polymerization starters. From 31P NMR analysis, the carboxyl groups of the succinyls and glutaryls held in the terminals of the isolated PHB were found to be capped with EG, giving the telechelic polyester with hydroxy functionalities. Based on these results, we propose a plausible mechanism of enzymatic polymerization in the microbial PHB synthesis in the presence of EG.
Keywords: Ralstonia eutropha; Ethylene glycol; Poly(3-hydroxybutyrate); NMR spectroscopy; MALDI-TOF MS; Glutarate;
Crystallinity and dimensional stability of biaxial oriented poly(lactic acid) films by Ching-Chun Tsai; Ren-Jye Wu; Hsiu-Yu Cheng; Shu-Chen Li; Ya-Yu Siao; Dan-Cheng Kong; Guang-Way Jang (1292-1298).
Transparent biaxial oriented poly(lactic acid) (BOPLA) films with improved dimensional stability were successfully prepared by controlling the crystallization of poly(lactic acid) (PLA). The crystalline morphology of PLA films can be manipulated by changing certain processing parameters, such as stretch ratio, heat setting temperatures, and heat setting time. Optical and mechanical properties as well as dimensional stability of the resulting polymer films are governed by their crystallinity and crystalline morphology. Crystallization behavior and kinetics of PLA, therefore, were investigated using wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) techniques. Mechanical properties and the dimensional stability of the biaxial oriented PLA films were obtained and correlated with their processing conditions. Poly(lactic acid) films prepared by melt extrusion methods have great potential for food packaging, shrink labeling and protective film applications. However, shrinkage at elevated processing temperature should be minimized to avoid puckering of the polymer film. Shrinkage of less than 2% was achieved for a BOPLA film stretched 300% in both directions at 75 °C and then annealed at 160 °C for 30 s. Fabrication, properties, and potential applications of a series of biodegradable films will be described.
Keywords: PLA; BOPLA; Crystallization; Shrinkage; Biaxial; Films;
Silver sulfide/poly(3-hydroxybutyrate) nanocomposites: Thermal stability and kinetic analysis of thermal degradation by S.Y. Yeo; W.L. Tan; M. Abu Bakar; J. Ismail (1299-1304).
The non-isothermal degradation of poly(3-hydroxybutyrate) (PHB) and silver sulfide/poly(3-hydroxybutyrate) (Ag2S/PHB) nanocomposites was investigated using thermogravimetric (TG) analysis. In the composite materials, Ag2S caused the degradation of PHB at a lower temperature as opposed to that of neat PHB. Moreover, an increase Ag2S loading in the PHB decreased the onset temperature (T onset) of thermal degradation, whereas it was raised upon augmenting the heating rate. From Kissinger plots, the observed trend of the degradation activation energy, E d, was attributed to polymer–particle surface interactions and the agglomeration of Ag2S. The thermal degradation rate constant, k, was linearly related to the Ag2S loading in PHB. Thus, the Ag2S nanoparticles effectively catalyzed the thermal degradation of PHB in the Ag2S/PHB nanocomposites. Differential scanning calorimetry (DSC) data also supported the catalytic property of Ag2S.
Keywords: PHB; Silver sulfide; Nanocomposite; Thermal degradation; Kissinger;
Engineering of pha operon on Cupriavidus necator chromosome for efficient biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from vegetable oil by Jun Mifune; Satoshi Nakamura; Toshiaki Fukui (1305-1312).
Cupriavidus necator H16CAc, previously constructed for production of poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate) [P(3HB-co-3HHx)] from soybean oil, was further engineered aiming to increase 3HHx composition in the copolyester. PHA synthase gene derived from Aeromonas caviae on the H16CAc chromosome was replaced by a gene encoding the N149S/D171G mutant and this recombination enhanced PHA productivity as well as slightly increased 3HHx composition. Manipulation of phaACn locus partially reduced the amount of 3HB unit concomitantly with relative increase of 3HHx composition, whereas deletion of phaB1Cn resulted in drastic decline of 3HB unit in P(3HB-co-3HHx). Insertion of phaJAc encoding (R)-specific enoyl-CoA hydratase from A. caviae into pha operon significantly enlarged 3HHx fraction without negative effects on the cell growth and polyester accumulation. Consequently, efficient production of P(3HB-co-3HHx) with 3HHx composition of 5.7–9.9 mol% was successfully achieved from soybean oil by the engineered strains.
Keywords: Polyhydroxyalkanoates; Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); pha operon; Cupriavidus necator; Ralstonia eutropha; Vegetable oil;
Influence of clay surface modification with urethane groups on the crystallization behavior of in situ polymerized poly(butylene succinate) nanocomposites by Sung Yeon Hwang; Myong Jo Ham; Seung Soon Im (1313-1320).
The crystallization behavior and fine structure of poly(butylene succinate) (PBS) nanocomposites with intercalation (30B20) and exfoliation (30BM20) morphologies, respectively, were investigated via isothermal crystallization testing and synchrotron small-angle X-ray scattering (SAXS). The dynamic viscosity of 30BM20 was markedly increased due to favorable interactions between the PBS matrix and the urethane group on the clay surface. However, 30BM20 showed similar crystallization rates to that of homo PBS because the surface urethane modification for 30BM20 precluded PBS matrix from the metallic group into clay to difficult in contact with each other, resulting in a reduced nucleation activity for the metallic group. SAXS profiles revealed that the long period and amorphous region size for 30B20 drastically decreased during isothermal crystallization. Meanwhile, 30BM20 was similar to those of homo PBS. This result also supports the above explanation for isothermal crystallization behavior. Considering all results in total, the introduction of a urethane modification considerably enhanced the physical properties of PBS but caused delayed crystallization rates.
Keywords: Nanocomposites; Clay modification; Crystallization behavior; SAXS;
Biobased myo-inositol as nucleator and stabilizer for poly(lactic acid) by Yuya Tachibana; Takuya Maeda; Osamu Ito; Yasukatsu Maeda; Masao Kunioka (1321-1329).
myo-Inositol made from a biomass feedstock was used as an additive for poly (l-lactic acid) (PLLA) which was also made from biomass feedstock. The crystallization and stabilization of PLLA by the addition of myo-inositol were evaluated by the melt injection molding process. While the isothermal crystallization of PLLA at 100 °C had finished over 14 min after melting, that of PLLA with 5 wt% myo-inositol finished within 2 min. The crystal growth of PLLA started when the myo-Inositol crystal was added, and the crystallization was promoted. Furthermore, the molecular weight of PLLA with myo-inositol did not decrease during the melt-mixed at 200 °C, different from that of PLLA without the myo-inositol. myo-Inositol prevented the degradation of PLLA during the thermal melting process. The biomass carbon ratio measured by the accelerator mass spectroscopy method showed that the PLLA with 5 wt% myo-inositol was a fully biobased material. It was demonstrated that myo-inositol was a multi-functional biobased additive for the modification of PLLA without decreasing its mechanical properties.
Keywords: Poly(l-lactic acid); myo-Inositol; Nucleator; Stabilizer; Biomass carbon ratio;
X-ray diffraction study on the thermal expansion behavior of cellulose Iβ and its high-temperature phase by Masahisa Wada; Ritsuko Hori; Ung-Jin Kim; Sono Sasaki (1330-1334).
Oriented films of cellulose prepared from algal cellulose were hydrothermally treated to convert them into highly crystalline cellulose Iβ. The lateral thermal expansion behavior of the prepared cellulose Iβ films was investigated using X-ray diffraction at temperatures from 20 to 300 °C. Cellulose Iβ was transformed into the high-temperature phase when the temperature was above 230 °C, allowing the lateral thermal expansion coefficient of cellulose Iβ and its high-temperature phase to be measured. For cellulose Iβ, the thermal expansion coefficients (TECs) of the a- and b-axes were αa = 9.8 × 10−5 °C−1 and αb = 1.2 × 10−5 °C−1, respectively. This anisotropic thermal expansion behavior in the lateral direction is ascribed to the crystal structure and to the hydrogen-bonding system of cellulose Iβ. For the high-temperature phase, the anisotropy was more conspicuous, and the TECs of the a- and b-axes were αa = 19.8 × 10−5 °C−1 and αb = −1.6 × 10−5 °C−1, respectively. Synchrotron X-ray fiber diffraction diagrams of the high-temperature phase were also recorded at 250 °C. The cellulose high-temperature phase is composed of a two-chain monoclinic unit cell, a = 0.819 nm, b = 0.818 nm, c (fiber repeat) = 1.037 nm, and γ = 96.4°, with space group = P21. The volume of this cell is 4.6% larger than that of cellulose Iβ at 30 °C.
Keywords: Cellulose Iβ; High-temperature phase; Phase transition; Synchrotron X-ray diffraction; Thermal expansion;
Isolation of polyhydroxyalkanoate-producing bacteria from a polluted soil and characterization of the isolated strain Bacillus cereus YB-4 by Kouhei Mizuno; Aya Ohta; Manami Hyakutake; Yousuke Ichinomiya; Takeharu Tsuge (1335-1339).
We describe the characterization of polyhydroxyalkanoate (PHA)-producing bacteria isolated from an ammunition-polluted soil in Kitakyushu City, Japan. Over 270 strains were evaluated for PHA accumulation based on a colony staining method using Nile red. Of these, nine strains were selected based on the intensity of Nile red fluorescence and the cells were quantitatively analyzed for PHA by gas chromatography. PHA accumulation was observed in five strains, all of which are inferred to be close to the Bacillus cereus group according to 16S rDNA sequence analysis. Interestingly, these strains produced a PHA copolymer, poly(3-hydroxybutyrae-co-3-hydroxyvalerate) [P(3HB-co-3HV)], with a 3HV fraction up to 2 mol% with glucose as a carbon source. Further characterization was performed on one isolate, B. cereus YB-4. Gel permeation chromatography analysis revealed that the number of average molecular weights of PHA accumulated in B. cereus YB-4 drastically changed from 722,000 to 85,000 over a 72-h cultivation period. Furthermore, the PHA synthase genes were cloned and the deduced amino acid sequences were determined. This study provides new insights into PHA biosynthesis by members of the B. cereus group.
Keywords: Polyhydroxyalkanoate; Bacillus; Molecular weight change; Polluted soil; Isolation;
Establishment of a metabolic pathway to introduce the 3-hydroxyhexanoate unit into LA-based polyesters via a reverse reaction of β-oxidation in Escherichia coli LS5218 by Fumi Shozui; Ken'ichiro Matsumoto; Ren Motohashi; Miwa Yamada; Seiichi Taguchi (1340-1344).
New lactate (LA)-based terpolymers, P[LA-co-3-hydroxybutyrate (3HB)-co-3-hydroxyhexananoate (3HHx)]s, were produced in recombinant Escherichia coli LS5218 harboring three genes encoding LA-polymerizing enzyme (LPE), propionyl-coenzyme A (CoA) transferase (PCT) and (R)-specific enoyl-CoA hydratase (PhaJ4). When the recombinant LS5218 was grown on glucose with the feeding of butyrate, 3HB-CoA and 3HHx-CoA were supplied, probably via reverse reactions of the β-oxidation pathway and PhaJ4. LPE copolymerized the two monomers 3HB-CoA and 3HHx-CoA with LA-CoA, which was generated by PCT, to yield the terpolymers. Gas chromatography analysis revealed that the terpolymers consisted of 2.7–34 mol% LA, 38–81 mol% 3HB and 17–33 mol% 3HHx units, which can be varied depending on the butyrate concentration fed in the medium. In addition, 1H-13C COSY NMR analysis provided evidence for a linkage between LA and 3HHx units in the polymer.
Keywords: Poly(LA-co-3HB-co-3HHx); LA-based polyester; PhaC1Ps(ST/QK); Microbial cell factory; Metabolic engineering; β-oxidation pathway;
Characterization of biosynthesized P(3HB-co-3HA)s swellable in organic solvents by Takeharu Tsuge; Yoshihiro Hamada; Yoriko Watanabe; Satoshi Tomizawa; Tetsuya Yamamoto; Hideki Abe (1345-1348).
Polyhydroxyalkanoate (PHA) copolymers consisting of (R)-3-hydroxybutyrate (3HB) and medium-chain-length (R)-3-hydroxyalkanoate (3HA), P(3HB-co-3HA), are usually solved in chloroform. However, we found that some of the P(3HB-co-3HA) aged for more than 1 month under ambient conditions were not solved in chloroform, but instead swelled when the 3HA fraction was over 14 mol%. On the basis of differential scanning calorimetry and wide-angle x-ray diffraction analyses, we predicted that swellable P(3HB-co-3HA) contained numerous P(3HB) microcrystals, which may form physical crosslinks between adjacent PHA polymer chains.
Keywords: Polyhydroxyalkanoate; Swelling; Organogel; Microcrystal;
Bioplastic biodegradation activity of anaerobic sludge prepared by preincubation at 55 °C for new anaerobic biodegradation test by Hisaaki Yagi; Fumi Ninomiya; Masahiro Funabashi; Masao Kunioka (1349-1355).
The new method to evaluate the anaerobic biodegradability of bioplastics, such as polycaprolactone (PCL) and poly (lactic acid) (PLA), under aquatic (slurry) conditions at 55 °C is applying. For this method, we prepared the sludge at 55 °C from the sludge at 37 °C by the method in which the sludge from the real tank operating at around 37 °C using cow manure and vegetable waste as the feed stock was preincubated at 55 °C. It was unknown at which stage the sludge during preincubation has the optimized anaerobic biodegradation activity of plastics. Four different stage sludges during preincubation (the sludge at 7 days after the start of preincubation at 55 °C, at 12 days, at 18 days, and at 40 days) were compared by the anaerobic biodegradation activity of PLA. The preincubated sludge at around 18 days (a gradual decrease in biogas evolution and a methane ratio over 60%) showed the highest biodegradation activity of PLA. In addition, the bacterial population in each sludge was analyzed by the denaturing gradient gel electrophoresis (DGGE) analysis of the amplified 16S rRNA gene fragments, however, the newly grown bacteria bands at 55 °C were not clearly detected.
Keywords: Anaerobic biodegradation; Poly (lactic acid); 16S rRNA; Methane fermentation;
Biodegradation-induced surface change of polymer microspheres and its influence on cell growth by Yu Zhang; Lei Sun; Jian Jiang; Xiaolin Zhang; Wenjun Ding; Zhihua Gan (1356-1364).
Biodegradable microspheres were fabricated by poly(ɛ-caprolactone) (PCL) homopolymer and poly(ɛ-caprolactone-b-ethylene oxide) (PCL-b-PEO) amphiphilic block copolymer. The regulation of microsphere surface morphology was successfully achieved by controlled enzymatic degradation. The morphological changes induced by biodegradation and their influences on the growth of MG-63 human osteosarcoma cells were studied. Results based on the evaluation of cytotoxicity and the morphological observation of MG-63 cells cultivated on microspheres showed better growth of cells on the surface of degraded microspheres than on the surface of those undegraded microspheres no matter they were fabricated by homopolymers or copolymers. The influences of morphological changes of microsphere surface before and after biodegradation on MG-63 cell growth were discussed. The results of this work indicated that the biodegradation-induced morphological changes of microspheres could be well controlled and were favorable for MG-63 cell attachment and proliferation.
Keywords: Biodegradable polymers; Microcarriers; Enzymatic degradation; Surface change; Cell culture;
Evaluation of jatropha oil to produce poly(3-hydroxybutyrate) by Cupriavidus necator H16 by Ko-Sin Ng; Wei-Yang Ooi; Lay-Koon Goh; Rajaiah Shenbagarathai; Kumar Sudesh (1365-1369).
Jatropha oil, a non-edible vegetable oil, may be an alternative substrate to food-grade oils for bioplastic production. Jatropha oil contains 93.9% palmitic acids, oleic acids and linoleic acids. High P(3HB) accumulation of 87 wt% from 13.1 g/L of cell dry weight (CDW) was obtained by Cupriavidus necator H16 when 12.5 g/L of jatropha oil and 0.54 g/L of urea were used. Lipase activity increased in the initial stages of P(3HB) production, when 1 g/L of jatropha oil was added to the preculture medium. Addition of oil in preculture did not affect final CDW or P(3HB) accumulation. P(3HB) production in a 10 L lab-scale fermenter gave a yield of 0.78 g P(3HB) per g jatropha oil used after 48 h. For the first time, this study proved that jatropha oil is a feasible and excellent carbon source for P(3HB) biosynthesis by C. necator H16 with potential for large-scale production. The toxins in jatropha oil did not affect the P(3HB) biosynthesis.
Keywords: Jatropha oil; Ratanjyot oil; Physic nut; Poly(3-hydroxybutyrate); Bioplastics;
Y443F mutation in the substrate-binding domain of extracellular PHB depolymerase enhances its PHB adsorption and disruption abilities by Tomohiro Hiraishi; Naoya Komiya; Mizuo Maeda (1370-1374).
Extracellular poly[(R)-3-hydroxybutyrate] (PHB) depolymerase (PhaZRpiT1) from Ralstonia pickettii T1 adsorbs to the PHB surface via its substrate-binding domain (SBD) and cleaves the PHB chain using its catalytic domain. Our previous study (Biomacromolecules 2010; 11: 113–119) has suggested that the hydrophobic interaction between the amino acid residues at positions 441, 443, and 445 in the SBD and the PHB surface plays a crucial role in facilitating the association phase of the enzyme adsorption process. In the present study, in order to improve PhaZRpiT1 for effective PHB degradation, we targeted Tyr at position 443 for substitution with a more highly hydrophobic amino acid residue because its hydrophobicity shows medium to high degree compared to those of general naturally occurring amino acid residues. We designed a mutant enzyme with an amino acid substitution at this position, taking the following factors into consideration: (1) to achieve higher hydrophobicity than the original residue, (2) to retain the β-sheet structure, and (3) to change as little as possible the volume of the amino acid residue after the substitution. As a result, the substitution of Tyr443 with Phe (Y443F) was considered to be appropriate. The purified Y443F enzyme showed identical CD spectrum and hydrolysis activity for a water-soluble substrate with the wild type, indicating that the mutation had no influence on the structure and the ester bond cleavage activity. In contrast, the Y443F enzyme had higher PHB degradation activity than the wild type. Kinetic analysis of PHB degradation suggests that this amino acid substitution promoted not only the adsorption of the mutant enzyme to PHB, but also the disruption of the PHB surface to enhance the hydrolysis of the PHB polymer chain.
Keywords: poly[(R)-3-hydroxybutyrate] (PHB); PHB depolymerase; Substrate-binding domain (SBD); Amino acid substitution; Adsorption; Disruption;
Highly selective transformation of poly[(R)-3-hydroxybutyric acid] into trans-crotonic acid by catalytic thermal degradation by Hidayah Ariffin; Haruo Nishida; Yoshihito Shirai; Mohd Ali Hassan (1375-1381).
Highly selective transformation of poly[(R)-3-hydroxybutyric acid] (PHB) into trans-crotonic acid was achieved by thermal degradation using Mg compounds: MgO and Mg(OH)2 as catalysts. Through catalytic action, not only the temperature and E a value of degradation were lowered by 40–50 °C and 11–14 kJ mol−1, respectively, but also significant changes in the selectivity of pyrolyzates were observed. Notably, Mg(OH)2 showed nearly complete selectivity (∼100%) to trans-crotonic acid. Kinetic analysis of TG profiles revealed that the catalytic thermal degradation of PHB was initiated by some random degradation reactions, followed by the unzipping β-elimination from crotonate chain-ends as a main process. It was suggested that the Mg catalysts promote the totality of the β-elimination reactions by acting throughout the beginning and main processes, resulting in a lowering in the degradation temperature and the completely selective transformation of PHB.
Keywords: Polyhydroxy butyrate; Catalytic depolymerization; Crotonic acid; Unzipping β-elimination; Kinetic analysis;
Biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer from wild-type Comamonas sp. EB172 by Mohd Rafein Zakaria; Hidayah Ariffin; Noor Azman Mohd Johar; Suraini Abd-Aziz; Haruo Nishida; Yoshihito Shirai; Mohd Ali Hassan (1382-1386).
Poly(3-hydroxybutyrate) [P(3HB)] homopolymer and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] copolymer was produced by Comamonas sp. EB172 using single and mixture of carbon sources. Poly(3-hydroxyvalerate) P(3HV) incorporation in the copolymer was obtained when propionic and valeric acid was used as precursors. Incorporation of 3HV fractions in the copolymer varied from 45 to 86 mol% when initial pH of the medium was regulated. In fed-batch cultivation, organic acids derived from anaerobically treated palm oil mill effluent (POME) were shown to be suitable carbon sources for polyhydroxyalkanoate (PHA) production by Comamonas sp. EB172. Number average molecular weight (M n) produced by the strain was in the range of 153–412 kDa with polydispersity index (M w/M n) in the range of 2.2–2.6, respectively. Incorporation of higher 3HV units improved the thermal stability of P(3HB-co-3HV) copolymer. Thus the newly isolated bacterium Comamonas sp. EB172 is a suitable candidate for PHA production using POME as renewable and alternative cheap raw materials.
Keywords: Polyhydroxyalkanoates; Poly(3-hydroxybutyrate-co-3-hydroxyvalerate); Palm oil mill effluent; Comamonas sp.; Characterization;
Chemical recycling of poly(lactic acid)-based polymer blends using environmentally benign catalysts by Yota Tsuneizumi; Maiko Kuwahara; Kohei Okamoto; Shuichi Matsumura (1387-1393).
Typical poly(l-lactic acid) (PLLA)-based polymer blends, PLLA/polyethylene (PE) and PLLA/poly(butylene succinate) (PBS), were degraded into each repolymerizable oligomer using environmentally benign catalysts, clay catalysts and enzymes, with the objective of developing a selective chemical recycling process. Two routes to selective chemical recycling of PLLA/PE blend were tested. One is the direct separation of PLLA and PE first by their different solubilities in toluene, followed by the chemical recycling of PLLA using montmorillonite K5 (MK5). The other is the selective degradation of PLLA in the PLLA/PE blend by MK5 in a toluene solution at 100 °C for 1 h forming the LA oligomer with a molecular weight of M n = 200–300 g/mol, which is the best M n for repolymerization. Thus regenerated PLLA had a M w of greater than 100,000 g/mol. The PE remained unchanged and was quantitatively recovered by the reprecipitation method for material recycling. In a similar procedure, chemical recycling of PLLA/PBS blend was also carried out and compared by two routes. One is the direct separation of PLLA and PBS by solubility in toluene. The other route is the sequential degradation of PLLA/PBS blend using a lipase first to degrade PBS into cyclic oligomer, which was then repolymerized to produce a PBS. Next, PLLA was degraded into repolymerizable LA oligomer by MK5. The former procedure was carried out using a single solvent; however, the latter required mixed solvents, which decreased the efficient recycling use of solvents.
Keywords: Chemical recycling; Polymer blends; Lipase; Montmorillonite; Poly(l-lactic acid); Polyethylene;
Comparison study of TEMPO-analogous compounds on oxidation efficiency of wood cellulose for preparation of cellulose nanofibrils by Shinichiro Iwamoto; Weihua Kai; Takuya Isogai; Tsuguyuki Saito; Akira Isogai; Tadahisa Iwata (1394-1398).
The effect of chemical structures of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical) derivatives and its analogous compounds on oxidation efficiency of C6 primary hydroxyls of wood cellulose was investigated using the NaClO/NaBr system at pH 10. Because the oxidation takes place selectively on the surfaces of cellulose microfibrils, individualized and surface-oxidized cellulose nanofibrils can be obtained by simple mechanical treatment in water, when sufficient amounts of carboxylate groups are formed homogeneously in cellulose microfibrils. 4-acetamide-TEMPO and 4-methoxy-TEMPO showed efficient catalytic behavior with short reaction times (<4 h) and high carboxylate contents (>1.1 mmol/g) in oxidation of wood cellulose, comparable to TEMPO. Correspondingly, these TEMPO derivatives as well as TEMPO gave high nanofibril yields >56%. On the other hand, the use of 4-hydroxy-TEMPO and 4-oxo-TEMPO resulted in the lowest efficiency in oxidation: oxidation times >24 h, carboxylate contents <0.3 mmol/g, and individualized and surface-oxidized nanofibril yields <2%.
Keywords: Cellulose; TEMPO-mediated oxidation; Nanofibrils; TEMPO derivatives;
Synthesis of high-performance green nanocomposites from renewable natural oils by Takashi Tsujimoto; Hiroshi Uyama; Shiro Kobayashi (1399-1405).
This paper describes preparation and properties of green nanocomposites from renewable resources. The nanocomposites were synthesized by an acid-catalyzed curing of epoxidized natural oils in the presence of silane coupling agents. The resulting nanocomposites were transparent and highly glossy. Their hardness and Young's modulus of the nanocomposite coatings improved, as compared with those only from the epoxidized natural oils. Dynamic viscoelasticity analysis and TEM observation showed the homogeneous structure of the nanocomposites. The properties of the nanocomposites were strongly affected by the structure and feed ratio of the monomers.
Keywords: Bio-based polymers; Epoxidized natural oil; Nanocomposite; Silane coupling agent;
Cellulose acetate butyrate as multifunctional additive for poly(butylene succinate) by melt blending: Mechanical properties, biomass carbon ratio, and control of biodegradability by Yuya Tachibana; Nguyen Thien Truong Giang; Fumi Ninomiya; Masahiro Funabashi; Masao Kunioka (1406-1413).
We have evaluated the plasticizing effect of poly(butylene succinate) (PBS) and cellulose acetate butyrate (CAB). PBS and CAB were mixed with a melt-kneading machine. The tensile strength and strain at break in the case of the blend with 10% CAB in the PBS matrix were 547% and 35 MPa. It showed that CAB acted as a plasticizer for PBS. The biomass carbon ratio of the blends measured by accelerator mass spectrometry based on ASTM D6866 showed that the biomass carbon derived from a part of the CAB corresponded to the theoretical value of the polymer blend. The biodegradation of PBS with the CAB melt blend powders was evaluated by a microbial oxidative degradation analyzer under controlled compost conditions based on ISO 14855-2. PBS with 10% CAB was not degraded within 60 days due to the addition of CAB that could control the biodegradability of the PBS.
Keywords: Poly(butylene succinate); Cellulose acetate butyrate; Plasticizer; Biomass carbon ratio; Biodegradability;
Solvent-induced morphological diversification in poly(l-lactide-b-ɛ-caprolactone) block copolymer thin films by Yoshihiro Kikkawa; Kenji Kurokawa; Ryota Kimura; Mayuko Takahashi; Masatoshi Kanesato; Hideki Abe (1414-1420).
Biodegradable block copolymer of poly(l-lactide-b-ɛ-caprolactone) (P(LA-b-CL)) was dissolved in various solvents with different solubility as well as volatility, and spin-cast on a highly oriented pyrolytic graphite (HOPG) to prepare thin films. The surface morphologies were observed by using atomic force microscopy (AFM) in a dynamic force (tapping) mode. Particle like morphology was found in the thin films prepared form the dichloromethane and acetone. Higher volatility of dichloromethane and acetone resulted in the reflection of the particle like objects in the solution to HOPG substrate. In contrast, the P(LA-b-CL)s in toluene and 1,4-dioxane exhibited different morphologies compared to those in dichloromethane and acetone. Lower volatility of toluene and 1,4-dioxane assisted the epitaxial crystallization of PCL component along the HOPG lattice, that was revealed by enzymatic degradation of PLLA component by proteinase K. Thus, adjusting the solubility and solvent volatility for the film formation provided morphological divergence of the P(LA-b-CL) block copolymer, and this technique would be applicable for the surface patterning of biodegradable polymers.
Keywords: Block copolymer; Atomic force microscopy; Thin film; Enzymatic degradation; Solvent;
Current advances in microbial cell factories for lactate-based polyesters driven by lactate-polymerizing enzymes: Towards the further creation of new LA-based polyesters by Seiichi Taguchi (1421-1428).
Polylactic acid (PLA), a representative bio-based polyester, has been commonly synthesized via a multi-step by chemical process. The current modes of generating PLA involve microbial fermentation of starting material, lactic acid (LA), followed by chemical ring-opening polymerization. Recently, one-pot complete bioprocess for LA-based polyesters has been established as a microbial cell factory (MCF). The concept is a process conversion from the usual chemical factory to the MCF. This new challenge was triggered by discovery of an engineered LA-polymerizing enzyme (LPE). The LPE was found as one of the members of an extensive mutant library that has been created through the long-term evolutionary engineering study of natural biopolyester-synthesizing enzymes. Needless to say, a strategic method of getting the beneficial mutation in the enzyme is of the utmost importance and an essential step towards accomplishing the desired purpose, the acquisition of the LA-polymerizing activity in this case. In this review, the structures and properties of LPE-catalyzed polymerization products will be discussed as well as backgrounds on establishment of the MCFs for synthesis of LA-based polyesters. Also, experimental strategies for enrichment of the LA fraction will be proposed to further advance the prototype of MCF based on the related metabolic pathways.
Keywords: Polylactic acid (PLA); Biopolymer; Polyhydroxyalkanoates (PHAs); PHA synthase; Enzyme engineering; Metabolic pathway engineering;
Tyrosine 105 of Paucimonas lemoignei PHB depolymerase PhaZ7 is essential for polymer binding by Siska Hermawan; Dieter Jendrossek (1429-1435).
The 3-dimensional structure of the Paucimonas lemoignei poly(3-hydroxybutyrate) (PHB) depolymerase PhaZ7 has significant similarity to Bacillus subtilis lipase LipA but differs from the latter by the presence of an additional domain. Analysis of this lid-like domain revealed the presence of many hydrophobic amino acid residues including Tyr105. In this study we constructed His-tag fusions of PhaZ7 for simplified purification and investigated the effect of amino acid exchange of eight tyrosine codons of the lid-like domain. Exchanges of Tyr103, Tyr172, Tyr173, Tyr203 or Tyr204 to alanine or serine had no phenotype but muteins with substitution of Tyr189, Tyr190 and Tyr105 to alanine showed a lag phase of the in vitro PHB depolymerase reaction. Replacement of Tyr105 by glutamate further increased the lag phase. Binding assays of the purified PHB depolymerase proteins with the natural substrate, native PHB granules, revealed a significantly reduced binding ability of the Tyr105Glu mutant compared to the wild type protein and confirmed that Tyr105 is involved in interaction with the polymeric substrate.
Keywords: Polyhydroxybutyrate; PHA; PHB depolymerase; PHB binding domain;
Improved synthesis of P(3HB-co-3HV-co-3HHx) terpolymers by mutant Cupriavidus necator using the PHA synthase gene of Chromobacterium sp. USM2 with high affinity towards 3HV by Kesaven Bhubalan; Devi-Nair Rathi; Hideki Abe; Tadahisa Iwata; Kumar Sudesh (1436-1442).
Unlike polyhydroxyalkanoates (PHAs) copolymers, the controlled and efficient synthesis of PHA terpolymers from triglycerides and fatty acids are yet to be established. This study demonstrates the production of P(3HB-co-3HV-co-3HHx) terpolymer with a wide range of 3HV monomer compositions from mixtures of crude palm kernel oil and 3HV precursors using a mutant Cupriavidus necator PHB−4 transformant harboring the PHA synthase gene (phaC) of a locally isolated Chromobacterium sp. USM2. The PHA synthase of Chromobacterium has an unusually high affinity towards 3HV monomer. P(3HB-co-3HV-co-3HHx) terpolymers with 3HV monomer composition ranging from 2 to 91 mol% were produced. Generation of 3HHx monomers was affected by the concentration and feeding time of 3HV precursor. P(3HB-co-24 mol% 3HV-co-7 mol% 3HHx) exhibited mechanical properties similar to that of common low-density polyethylene. P(3HB-co-3HV-co-3HHx) terpolymers with a wide range of 3HV molar fraction had been successfully synthesized by adding lower concentrations of 3HV precursors and using a PHA synthase with high affinity towards 3HV monomer.
Keywords: Chromobacterium sp.; 3-Hydroxyvalerate; 3-Hydroxyhexanoate; Crude palm kernel oil; Sodium valerate;