Assessing the mechanical,phase inversion,and rheological properties of poly-[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate] (PHBV) blended with poly-(l-lactic acid) (PLA)

Poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly-(l-lactic acid) (PLA) have attracted much interest in recent years since they are biodegradable, thus can replace synthetic non-degradable materials. In this study, improvements of PHBV, mechanical, phase inversions, and rheological properties were investigated after blending with PLA in varying ratio’s. Three different blends of commercially available PLAs with 92–98% l-lactide units and one grade of PHB with 5% valerate content were blended using a micro-compounder at 175 °C. The composition of PHBV in blends ranged from 50% to 80%. With the addition of PLA, increases in the flexural strength and elastic modulus were observed for several blends, while minor to no changes were detected in the elongation at break and tensile strength as compared to pure PHBV material. Like many conventional plastics, the complex viscosity decreased with increasing rotational frequency due to decreasing entanglements and molecular weight. The complex viscosity with respect to time was very stable for the blends, but no improvements in the PHBV viscosity were observed with the addition of PLA at 170 °C. Three phase inversion models were used to predict the continuity of the blends, and the results showed both dual- and PLA-continuity phase for the blends. In summary, the mechanical results showed improvements in the tensile and flexural properties, while the rheological observation showed minor improvements in the complex viscosity for numerous concentrations.     

Tailoring the properties of electrospun PHBV mats: Co-solution blending and selective removal of PEO

Microstructure, surface topography, thermal and mechanical features of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) electrospun non-woven mats were modified, modulated and tailored through blending with different polyethylene oxide (PEO) amounts (20, 30 and 50% wt/wt). The optimal parameters of the soaking protocol for the selective removal of the sacrificial polymer were accurately identified by means of scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy, simultaneous thermogravimetric and differential analyses (TG-DTA) and differential scanning calorimetry (DSC). The complete PEO removal after soaking in H₂O for 7 days with daily refreshment was confirmed. The resulting samples were only comprised of PHBV fibers characterized by a remarkable decrease of the average size with respect to the respective blends. Their surface topography was corrugated and rough and presented nodules, pits, nanopores, shallow and elongated nanostructured indents/grooves along the fiber axis. A remarkable reduction (>75%) of the tensile modulus (E) of electrospun PHBV mats (15–20 MPa) was obtained, maintaining comparable elongation at break (ε_max) values (20–30%).     

Reducing the formation of six-membered ring ester during thermal degradation of biodegradable PHBV to enhance its thermal stability

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity and plastic-like properties. However, PHBV is unstable above 160 °C during melt processing at a temperature above the melting temperature, which restricts practical applications as a commodity material. It is widely believed that thermal degradation of PHBV occurs almost exclusively via a random chain scission mechanism involving a six-membered ring transition state. Here, 2,2′-bis(2-oxazoline) (BOX) was selected to modify PHBV to control the formation of six-membered ring ester during thermal degradation. The resulting hydroxyl-terminated PHBVs (HT-PHBVs) had improved thermal stability due to a decrease in the negative inductive effect of the neighboring group of methylene groups at the β-position to the ester oxygen, and a decrease in the electron-denoting effect of substituent group of carbon atoms at α-position to the ester oxygen. The optimal reaction temperature and time were determined to be 95 °C and 6 h, respectively. Compared with those of original PHBV, the temperature determined at 5% weight loss (T_5%), the initial decomposition temperature (T₀), the maximum decomposition temperature (T_max), the complete decomposition temperature (T_f) of HT-PHBV prepared under the optimal conditions increased by 31, 24, 19 and 19.1 °C, respectively.     

Effect of thermal degradation on rheological properties for poly(3-hydroxybutyrate)

Thermal degradation at processing temperature and the effect on the rheological properties for poly(3-hydroxybutyrate) have been studied by means of oscillatory shear modulus and capillary extrusion properties, with the aid of molecular weight measurements. Thermal history at processing temperature depresses the viscosity because of random chain scission. As a result, gross melt fracture hardly takes place with increasing the residence time in a capillary rheometer. Moreover, it was also found that the molecular weight distribution is independent of the residence time, whereas the inverse of the average molecular weight is proportional to the residence time. Prediction of average molecular weight with a constant molecular weight distribution makes it possible to calculate the flow curve following generalized Newtonian fluid equation proposed by Carreau as a function of temperature as well as the residence time.     

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from cottonseed oil and valeric acid in batch culture of Ralstonia sp. strain JC-64

A Ralstonia sp. strain JC-64 that is capable of accumulating poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[3HB-co-3HV]) from cottonseed oil and valeric acid was isolated. By using a high limiting-nitrogen (HLN) mineral medium as the medium for the second stage of the fermentation process and by adding the two carbon sources at different times, a range of copolymers with 12–62 mol% of 3HV were produced from a series of HLN mineral mediums containing different compositions of cottonseed oil and valeric acid by Ralstonia sp. JC-64. The melting temperature (T _m ) of polyhydroxybutyrate from cottonseed oil was 174°C and that of P(3HB-co-3HV) with the highest 3HV-mol fraction (62%) was 81°C.     

Controlling the size of poly(hydroxybutyrate-co-hydroxyvalerate) nanoparticles prepared by emulsification–diffusion technique using ethanol as surface agent

Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBHV) nanospheres and oily nanocapsules were prepared by emulsification–diffusion technique. Controlled particle sizes were obtained employing binary mixtures of solvents (chloroform:ethanol) in the organic phase. Ethanol was chosen because of its dipole–dipole interaction with chloroform and its hydrogen bond with water. The smallest particles (from 253 to 493 nm) were obtained using a mixture of solvents composed of 70% ethanol and 30% chloroform (v/v) in the organic phase, while the largest particles (from 896 to 1568 nm) were obtained using chloroform exclusively. Independently of the organic phase composition, the nanoparticles showed unimodal distributions. Optical microscopy showed that the size of the primary emulsion droplets of the nanosphere formulations decreased with increasing ethanol concentrations in the organic phase. A simple empirical equation was developed correlating the nanoparticle diameters with the surface tension gradient coefficient multiplied by the ethanol molar concentration in the organic phase. The strategy showed that the control of the nanoparticle diameters, using emulsification–diffusion technique, could be achieved by adjusting the surface tension of the organic phase.     

Changes in the mechanical properties of compression moulded samples of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) degraded by Streptomyces omiyaensis SSM 5670

Streptomyces omiyaensis SSM 5670 was characterized by its ability to use compression moulded samples of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as its sole carbon source. Biodegradation of PHBV in liquid mineral salts medium was investigated using scanning electron microscopy, gravimetric measurements, capillary viscometry, tensile testing and wide angle X-ray spectroscopy. The biodegradation of PHBV proceeds via surface erosion mechanism, resulting in the formation of pits by microbial attack. PHBV specimens lost about 45% of their original weight after 45 days of exposure. During the degradation process the elastic modulus reduces less than 10%. The formation of pores and microcracks initiated at the degraded pits determines the reduction of the elongation and stress at break. However, the true stress at break is practically independent of the degradation time. No significant changes of PHBV molecular weight or crystallinity were observed during biodegradation. The polymer chain cleavage occurred only at the specimen surface and does not discriminate between crystalline and amorphous states.     

Sphaerotilus natans isolated from activated sludge and its production of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)

Sphaerotilus natans is a sheathed bacterium existing in the activated sludge of wastewater treatment plants. IT is one of the filamentous bacteria causing the bulking and foaming difficulties of activated sludge. Isolating the strain and culturing it in an axenic environment could not only provide the metabolic knowledge of the strains that would be useful in the development of wastewater treatment methods, but also could enable us to gain an understanding of the mechanism by which poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (poly[3-HB-co-3-HV]) is produced by this strain. This article reports the screening and isolation of the strain from the activated sludge using the Nile blue staining method together with Fourier transform infrared analysis. We investigated the ability of the selected strain to produce poly(3-HB-co-3-HV) copolymer using glucose and peptone, or by adding valeric acid or sodium propionate as precursor. Proper precursor feeding could dramatically enhance its 3HV content in the copolymer P(3HB-co-3HV). By controlling the different feeding times in fed-batch fermentation, different desired copolymers were obtained with 15, 40, and 70% 3HV mole fraction of the copolymer. Polymer properties were analyzed by gas chromatography, differential scanning calorimetry, thermo-gravimetry, and nuclear magnetic resonance analysis. Open laboratory of Chirotechnology of the Institute of Molecular Technology for Drug Discovery and Synthesis The University Grants Committee Area of Excellence Scheme (Hong Kong).     

Biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer from wild-type Comamonas sp. EB172

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.     

Fracture evaluation of plasticized polylactic acid / poly (3-HYDROXYBUTYRATE) blends for commodities replacement in packaging applications

Nowadays, scientific and technological efforts are being carried out to diminish serious ecological problems caused by indiscriminate use of non-biocompostable polymers in the packaging industry. In this sense, novel biodegradable blends of different composition based on poly(lactic acid) (PLA), poly(3-hydroxybutyrate) (PHB) and tributyrin (TB) are developed and here proposed as an eco-friendly alternative. Materials are characterized by fracture experiments under quasi-static and biaxial impact loading. Fracture behavior is analyzed together with thermal, tensile and water permeation properties to evaluate their potential in-service performance. TB_PLA/PHB blends with 15 wt% TB exhibit better permeation and fracture toughness than currently used bio-based polymers, being in the range of polyethylene properties. Results highlight the potential of these new blends broadening the current application field of PLA.     

THERMAL AND MECHANICAL PROPERTIES OF SOME POLY(METHYL ACRYLATE)/SILICA COMPOSITES WITH INTENTIONALLY SUPPRESSED INTERFACIAL BONDING

ABSTRACT

Poly(methyl acrylate)/silica composites were prepared using a silane coupling agent designed to suppress the bonding between the silica and the acrylate elastomeric matrix. These composites were characterized using a scanning electron microscope, a differential scanning calorimeter, thermogravimetric analyzer, and an Instron mechanical tester. The mechanical properties of these materials were much poorer than those of the corresponding composite having a silane giving strong interfacial bonding, thus documenting the effects of these interactions on the reinforcement of a typical elastomeric material.     

Novel organic material with potential NLO application - electronic and spectroscopic properties

Novel dicyanoisophorone derivative, (E)-2-(3-(4-aminostyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile, is synthesized and its structure elucidated by means of conventional and linear polarized IR-spectroscopy of oriented colloids in nematic host, ¹H, ¹³C, ¹H, ¹H-COSY NMR, HPLC tandem ESI MS-MS spectrometry, UV-VIS and thermal methods. Ab initio and DFT level of theory are used to theoretically obtain the electronic structure and optical properties, both in ground and exited state, of the compound.      

Study on formation of poly(β-hydroxybutyrate-co-hydroxyvalerate) (PHBV) fiber

In this paper, the crystallization behavior, thermal degradation properties, rheological behavior and the spinnability of poly(β-hydroxybutyrate-co-hydroxyvalerate) (PHBV) fiber were studied. Experimental results indicated that the spherulite growth rate of PHBV was very slow and its size was very large. PHBV began to degrade above 170°C. The flowing curve indicated that the processing temperature and the residential time had important effects on PHBV melts. When the equipment of melting spinning was improved and processing conditions were strictly controlled, the mechanical properties of the PHBV filament can comply with the requirements of the American Pharmacopoeia. __________ Translated from Journal of Donghua University (Natural Science Edition), 2007, 33(4): 425–430     

Y443F mutation in the substrate-binding domain of extracellular PHB depolymerase enhances its PHB adsorption and disruption abilities

Extracellular poly[(R)-3-hydroxybutyrate] (PHB) depolymerase (PhaZ_RpiT1) 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 PhaZ_RpiT1 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.     

Micellization and controlled release properties of methoxy poly(ethylene glycol)-b-poly(D,L-lactide-co-trimethylene carbonate)

Amphiphilic block copolymers composed of D,L-lactide, trimethylene carbonate and the methoxy poly (ethylene glycol) (PETLA) were synthesized with ringopening copolymerization. Studies on the micellization and drug-controlled release behavior of PETLA were performed. Both of the copolymers and the micelles were characterized with the methods of ¹H nuclear magnetic resonance (¹H-NMR), fluorescence spectroscopy, gel permeation chromatographic (GPC), dynamic light scattering (DLS), transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV). As a result, the critical micelle concentration of the copolymer was decreased with the increase of the hydrophobic chain length. DLS results indicated the diameters of the micelle were increased with increasing hydrophobic length. TEM photographs illustrated that micelles MT1 were regularly spherical with the diameter from 30 nm to 40 nm. Taking 9-nitro-20(S)-camptothecin (9-NC) for the model drug, the release profiles in vitro show that the release behavior from micelles was controllable and nearly in zero order after the initial burst release. __________ Translated from Acta Polymerica Sinica, 2008, 2 (in Chinese)     

Thermal and mechanical characterization of plasticized poly (L-lactide-co-D,L-lactide) films for food packaging

In this work amorphous poly(L-lactide-co-D,L-lactide) (PLLA/PDLLA) was blended with four different commercial adipates to obtain films with enhanced mechanical and thermal properties. Efficiency of plasticizers was evaluated by studying their compatibility with the polymer and their effect on its glass transition temperature. All plasticizers were compatible with the matrix up to a critical composition depending on its molar mass. The addition of plasticizers caused a decrease in elastic modulus and tensile stress, meanwhile elongation at break had a maximum increase for polyadipates with the lower molar mass. Monomeric adipate showed some migration at concentration higher than 10 mass%, while the addition of the higher molar mass plasticizer lead to eventual phase separation. Polyadipates with low molar mass showed a promising behaviour to overcome the brittleness in PLLA/PDLLA films.     

Fabrication and enhanced mechanical properties of porous PLA/PEG copolymer reinforced with bacterial cellulose nanofibers for soft tissue engineering applications

A new class of polylactic acid (PLA)/polyethylene glycol (PEG) copolymer reinforced with bacterial cellulose nanofibers (BC) was prepared using a solvent casting and particulate leaching methods. Four weight fractions of BC (1, 2.5, 5, and 10 wt%) were incorporated into copolymer via silane coupling agent. Mechanical properties were evaluated using response surface method (RSM) to optimize the impact of pore size, porosity, and BC contents. Compressive strength obtained for PLA/PEG-5 BC wt% was 9.8 MPa, which significantly dropped after developing a porous structure to 4.9 MPa. Nielson model was applied to investigate the BC stress concentration on the PLA/PEG. Likewise, krenche and Hapli-Tasi model were employed to investigate the BC nanofiber reinforcement and BC orientation into PLA/PEG chains. The optimal parameters of the experiment results found to be 5 wt% for BC, 230 μm for pore size, and 80% for porosity. Scanning electron microscopy (SEM) micrograph indicates that uniform pore size and regular pore shape were achieved after an addition of BC-5% into PLA/PEG. The weight loss of copolymer-BC with scaffolds enhanced to the double values, compared with PLA/PEG-BC % without scaffolds. Differential Scanning Calorimetric (DSC) results revealed that the BC nanofiber improved glass transition temperature (T_g) 57 °C, melting temperature (T_m) 171 °C, and crystallinity (χ %) 43% of PLA/PEG reinforced-BC-5%.     

Tensile properties,thermal and morphological analysis of thermoplastic polyurethane films reinforced with multiwalled carbon nanotubes

The paper reports on thermal, tensile and morphological properties of thermoplastic polyurethane (TPU) based films obtained by melt-compounding and chill-roll extrusion. Composite films containing up to 1 wt% of multiwalled carbon nanotubes (MWNTs) are characterized in terms of thermal properties, tensile behavior and morphological issues taking the neat TPU film as the reference material.     

Development and thermal behaviour of ternary PLA matrix composites

Biodegradable PLA composites were prepared using microcrystalline cellulose (MCC) and silver (Ag) nanoparticles. The main objective of the present study is to develop new biopolymer composites with good mechanical properties, thermal stability, maintaining the optical transparency and also providing antimicrobial properties through silver nanoparticle introduction. Composites were prepared with 1%wt of Ag nanoparticles and 5%wt of MCC using a twin-screw microextruder; film parameters were optimized in order to obtain a thickness range between 20 and 60 μm.PLA composites maintained optical transparency properties of the matrix, while MCC was able to reduce polymer permeability. Thermal analysis revealed that MCC increased PLA crystallinity and the mechanical properties of the composites demonstrated that tensile modulus was improved by microcrystalline cellulose.     

Stereochemistry of ketone olefination with methyl trimethylsilylacetate

High (Z)-stereoselectivity of olefination of methyl α-phenylthioalkyl and methyl α-phenylthioalkenyl ketones with methyl trimethylsilylacetate decreases in the case of ketones containing a higher alkyl-substituent in place of the methyl group. Dedicated to Corresponding Member of the Russian Academy of Sciences E. P. Serebryakov on the occasion of his 70th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 1020–1021, April, 2005.