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%).     

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.     

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.     

Study of enzymatic degradation of microbial copolyesters consisting of 3-hydroxybutyrate and medium-chain-length 3-hydroxyalkanoates

Enzymatic degradation of poly(3-hydroxybutyrate-co-3-hydroxyalkanoates) (PHBA) biopolyester consisting of 3-hydroxybutyrate (HB) and 15 mol% medium-chain-length 3-hydroxyalkanoates (HA) was studied using a polyhydroxyalkanoates (PHA) depolymerase produced by Ralstonia pickettii T1. It was found that PHBA films did not lose their weight after 25 h of depolymerase treatment. In contrast, three commercially available PHAs including poly-3-hydroxybutyrate (PHB), poly(3-hydroxybutyrate-19 mol% 3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-19 mol% 3-hydroxyhexanoate) (PHBHHx) lost 75%, 94% and 39% of their original weights. Slow degradation of PHBA was also confirmed by the absence of HA monomers, dimers or trimers as degradation products in their depolymerase solution compared with abundance of degradation products released by the other three PHAs under the same condition. Surface erosion of PHBA was only observed after 48 h of enzymatic treatment compared with those of PHB, PHBV and PHBHHx which already had obvious surface changes after 7.5 h of same treatment. Although the crystallinities of PHB, PHBV, PHBHHx and PHBA were in the order PHB > PHBV > PHBHHx > PHBA valued at 55.8%, 47.8%, 45.9% and 40.9%, respectively, the order of degradability was PHBV > PHB > PHBHHx > PHBA. It can be proposed that PHA enzymatic degradation using this depolymerase was structure related: longer side-chain PHA including PHBHHx and PHBA was less favorable for the depolymerase degradation, longer the side chain, less the biodegradation.     

Mechanical, thermal and degradation properties of poly(d,l-lactide)/poly(hydroxybutyrate-co-hydroxyvalerate)/poly(ethylene glycol) blend

The mechanical, thermal and biodegradable properties of poly(d,l-lactide) (PDLLA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ethylene glycol) (PEG) blends were studied. The influence of PEG on the tensile and impact strengths of the blends was investigated. The results showed that the toughness and elongation at break of the PDLLA/PHBV (70/30) blends were greatly improved by the addition of PEG, and the notched Izod impact strength increased about 400% and the elongation at break increased from 2.1% to 237.0%. The thermal and degradation properties of the blends were investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA), it was found that the thermal stability of PHBV in the presence of PDLLA was improved. The degradation test showed that the addition of PEG could notably accelerate the biodegradation of the blends in the soil at room temperature, and the mass loss is about 20% after 30 days of the storage.     

Thermal and mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) plasticized by biodegradable soybean oils

The effects of soybean oil (SO) and epoxidized soybean oil(ESO) as biodegradable plasticizers for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were studied using thermal and mechanical analyses. PHBV/SO and PHBV/ESO blends were prepared by evaporating solvent from blend solutions. The levels of additive in the blend varied from 5% to 30%. As a plasticizer for PHBV, ESO was more effective than SO in depression of the glass transition temperature as well as in increasing the elongation at break and the impact strength of the films with increasing levels of additive. Biodegradation of the plasticized PHBV films was carried out by accelerated compost method. The degradation rates of the blend films with SO or ESO were found to be faster than that of PHBV film. From the thermogravimetric analysis, it was found that the thermal reaction between the epoxide groups of ESO and PHBV fragments with carboxylic chain ends, occurred during the degradation of PHBV/ESO blends.     

STUDY ON BIODEGRADABILITY OF POLY（3-HYDROXYBUTYRATE-co-3-HYDROXYVALERATE）／ORGANOPHILIC MONTMORILLONITE NANOCOMPOSITES

Poly (3-lydroxybutyrate-co-3-hydroxyvalerate)/Organophilic montmorillonite(PHBV/OMMT) nanocomposites were prepared and the biodegradability of the PHBV/OMMT nanocomposites was studied by a cultivation degrading method in soil suspension The relationship between structure and biodegradability of PHBV/OMMT nanocomposites was investigated. The results showed that the biodegradability of PHBV/OMMT nanocomposites decreased with increasing amount of OMMT and it was related to the number of PHBV degrading microorganisms in degradation environment, the anti-microbial property of OMMT and the degree of crystallinity of the nanocomposites.     

STUDY ON BIODEGRADABILITY OF POLY (3-HYDROXYBUTYRATE-co-3-HYDROXYVALERATE)/ORGANOPHILIC MONTMORILLONITE NANOCOMPOSITES

1. INTRODUCTION Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has been recognized as apotential environment-friendly substitute for traditional plastics. The structure, mechanicalproperties and biodegradability of PHBV as biodegradable plastic have been reported by many groups [1-3]. However, PHBV presents some problems, such as high cost, slow crystallization rate, relatively difficult processing and high degree of crystallinity. Therefore, it is difficult to use PHBV widel…     

PHBV/Sol-gel Bioglass多孔材料在模拟生理溶液中的化学反应研究

3-羟基丁酸-co-3-羟基戊酸共聚物(PHBV)/生物活性玻璃(SGBG)是一种用于骨和软骨组织工程支架的新型多孔复合材料,本文探讨了PHBV/SGBG在模拟生理溶液中的一系列化学反应,以及多孔材料在模拟生理溶液中浸泡后的成分和结构变化.研究结果表明,在SBF溶液中浸泡后,SGBG与SBF溶液的离子交换反应和PHBV的降解反应使SBF溶液的离子浓度发生变化,并在PHBV/SGBG表面形成了结晶态类骨碳酸羟基磷灰石.     

Thermal properties and degradability of poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends

Poly(propylene carbonate)/poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PPC/PHBV) blends were prepared via the solution casting method at different proportions. Their thermal characteristics were studied by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The degradability of the blends was investigated in soil suspension cultivation and in vitro degradation testing. The changes of structure and molecular weight for blends were also studied by ¹H nuclear magnetic resonance spectroscopy (¹H NMR), scanning electron microscopy (SEM) and gel permeation chromatography (GPC) before and after degradation. Although the PPC/PHBV blends were immiscible, the addition of PHBV could improve the thermal stability of PPC. PHBV was degraded mainly by the action of microbial enzymes in the soil suspension, which biodegraded it more rapidly than PPC in a natural environment. PPC was degraded mainly by chemical hydrolysis and random hydrolytic scission of chains in the PBS solution in vitro, and degradation of PPC was more rapid than that of PHBV in a simulated physiological environment.     

PPDO/OMMT纳米复合材料在微生物环境下的降解行为

采用微生物水性培养液降解实验法对聚对二氧环己酮/有机蒙脱土(PPDO/OMMT)纳米复合材料的生物降解性能进行了研究.通过质量、特性黏数、pH、热分析和电子扫描显微镜(SEM)研究了试样的降解过程.结果表明,在本实验条件下,PPDO/OMMT纳米复合材料降解性随着OMMT含量的增加而增加.降解90天,在微生物水性培养液...     

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n=3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U∗=1500 cal mol⁻¹, T_∞=30 K and T_g=278 K, the nucleation parameter K_g was determined, which was found to be 3.14 ± 0.07 × 10⁵ (K²), lower than that for pure PHB. The surface-free energy σ=2.55×10⁻² J m⁻² and σ_e=2.70±0.06×10⁻² J m⁻² were estimated and the work of chain-folding (q=12.5±0.2 kJ mol⁻¹) was derived from σ_e, and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.     

Characterization and enzymatic degradation of microbial copolyester P(3HB-co-3HV)s produced by metabolic reaction model-based system

The two types of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)s [P(3HB-co-3HV)s] were produced by Paracoccus denitrificans ATCC 17741 using two different feeding methods. The produced P(3HB-co-3HV)s were fractionated and the copolymer sequence distributions were analyzed by ¹H and ¹³C NMR spectroscopy. It was found that the P(3HB-co-3HV) samples produced by conventional feeding method were statistically random copolymers. The sequence distributions of P(3HB-co-3HV) samples produced by optimization method were different from random P(3HB-co-3HV)s. The thermal properties and melting behaviors were analyzed by differential scanning calorimetry (DSC). These results demonstrated that P(3HB-co-3HV) samples produced by optimization method are close in nature to P(3HB-co-3HV)s rich in long-sequence of block 3HB units, but less in 3HV random regions. The enzymatic degradation profile of P(3HB-co-3HV) films was investigated in the presence of 3-hydroxybutyrate depolymerase from Pseudomonase lemoignei. The degradation process was observed by monitoring the time-dependent change in the weight loss of copolymer films. The surface erosion of copolymer films was qualitatively monitored by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The highest degradation rate of 2.6% per day was observed for random P(3HB-co-38%3HV) produced by conventional method. In comparison, the hydrolysis degradation rates of random P(3HB-co-3HV)s were about one time faster than those of P(3HB-co-3HV)s produced by optimization method.     

Biodegradation of microbial polyesters P(3HB) and P(3HB-co-3HV) under the tropical climate environment

The biodegradation of poly(3-hydroxybutyrate), P(3HB), and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV) produced by a locally isolated bacteria identified as Erwinia sp. USMI-20 were carried out by using soil burial test and immersion test method at various places under the tropical environment in West Sumatra, Indonesia. The isolation of P(3HA)-degrading microorganisms was done by the in vitro rapid plate test method and was further characterized by using biochemical reactions. Our results showed that P(3HB) biodegraded at a rate of 3.6% per week in activated sludge, 1.9% per week in soil, 1.5% per week in lake water and 0.8% per week in Indian Ocean sea water. The degradation rates for P(3HB-co-3HV) were 17.8% per week in activated sludge, 6.7% per week in soil, 3.2% per week in lake water and 2.7% per week in Indian Ocean sea water. The biodegradation of both polymers were highest after burial into activated sludge with a half-life (T_1/2) of 14 weeks and the time for 100% degradation (T_100%) of 28 weeks for P(3HB), and a T_1/2 of 3 weeks and T_100% at 6 weeks for P(3HB-co-3HV). In this study, 10 bacteria which were responsible for the biodegradation of P(3HB) and P(3HB-co-3HV) film were isolated and identified from the various places studied under the tropical environment. They were Bacillus sp. FAAC-2202, Enterobacter sp. FAAC-2207, Bacillus sp. FAAC-2209 and Proteus sp. FAAC-2203 obtained from activated sludge, Bacillus sp. FAAC-2201 and Alcaligenes sp. FAAC-2210 from soil, Alcaligenes sp. FAAC-2205, Micrococcus sp. FAAC-2206 and Pseudomonas sp. FAAC-2208 from lake water and Proteus sp. FAAC-2204 from Indian Ocean sea water.     

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.     

Crystallization behavior and biodegradation of poly(3-hydroxybutyrate) and poly(ethylene glycol) multiblock copolymers

Block copolymerization by using isocyanates is an effective method for incorporating PHB and PEG because it can prepare copolymers with good properties, such as toughness, strength, and so on. In this study, we adopted soil suspension system to estimate the biodegradability of a series of PHB/PEG multiblock copolymers with different compositions and block lengths. In the degradation process, the changes in weight loss, molecular weight, and tensile strength were periodically measured to determine the biodegradability, and the surface morphology was also observed by SEM. In contrast to pure PHB, the weight loss of the copolymer was relatively lower. On the other hand, the tensile strength and molecular weight experienced apparent decrease, and for BHG1000-3-1, they reached 46.7% and 77.7% of the initial value, respectively. SEM observation showed that the surface was covered with numerous erosion pits. All these indicate that the degradation indeed took place and long-chain molecules have been hydrolyzed into shorter ones. The crystallization behavior was also investigated by DSC and WAXD. The results showed that both the segments, PEG and PHB, can form crystalline phases at lower PHB contents ranging from 29% to 44%, and when PHB component was more than 60%, only PHB phase can crystallize.     

Synthesis and characterization of biodegradable poly(?-caprolactone-co-β-butyrolactone)-based polyurethane

Poly(?-caprolactone-co-β-butyrolactone) (PCLBL)-based polyurethane (PCLBL-PU) was synthesized and its tensile properties and hydrolytic degradability were investigated in an attempt to improve the degradability of poly(?-caprolactone)-based polyurethane (PCL-PU). PCLBL was synthesized by the ring-opening polymerization of ?-caprolactone (CL) and β-butyrolactone (BL) with stannous octoate as a catalyst. The introduction of a small amount of BL units significantly decreased the crystallinity of PCLBL. The crystallinity of the soft segment of PCLBL-PU also decreased with increasing BL content, and thus its hydrolytic degradation rate was dramatically increased. PCLBL-PU polymerized with PCLBL containing 5.7 mol% of BL units showed very similar tensile properties to PCL-PU, but its hydrolytic degradation rate increased by 100% at 45 °C.     

Synergistic effect of compatibilizer and sepiolite on the morphology of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(butylene succinate) blends

Blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(butylene succinate) (PBS) with different PHBV/PBS weight ratios (100/0, 75/25, 50/50 and 0/100) were elaborated by melt mixing. The morphological investigation of the different samples, in comparison with that of neat PHBV and neat PBS, pointed out that PHBV/PBS blends form a biphasic system over the whole composition range. Low amount of compatibilizing agent (5 wt%), obtained by grafting maleic anhydride (MA) onto PHBV, i.e. PHBV-g-MA, was used for improving the miscibility between the two components of the blend. The incorporation of a fibrous filler as the sepiolite, easily dispersible in a polymer matrix, was also investigated. The morphology of the different blends as well as the evolution of their material properties were discussed in terms of the sepiolite and compatibilizing agent contents. The dispersion of PBS in the PHBV matrix markedly became finer with incorporation of sepiolite and PHBV-g-MA, due to enhanced interactions between the components. This paper highlighted a synergistic effect induced by the presence of both compatibilizer and sepiolite leading to an improved miscibility of the two blend components. The resulting properties were correlated with the morphology observed for the different blends.     

Synthesis and characterization of biodegradable poly(butylene succinate-co-butylene fumarate)s

A series of aliphatic biodegradable polyesters modified with fumaric residues was synthesized by transesterification in the melt of dimethyl succinate, dimethyl fumarate and 1,4-butanediol. The amount of unsaturation, originating from the fumaric acid residues in the polyesters chains was varied from 5 to 20 mol%. The molecular structure and composition of the polyesters were determined by ¹H NMR spectroscopy. The effects of the content of fumaric residues on the thermal and thermo-oxidative properties of the synthesized polyesters were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis. The degree of crystallinity was determined by DSC and wide angle X-ray scattering. The degrees of crystallinity of the unsaturated copolyesters were reduced, while the melting temperatures were higher in comparison to poly(butylene succinate). Biodegradation of the synthesized copolyesters was estimated in enzymatic degradation tests using a buffer solution with Rhizopus arrhizus lipase at 37 °C. Although the degree of crystallinity of the copolyesters decreases slightly with increasing unsaturation, the biodegradation is not enhanced suggesting that not only the chemical structure and molecular stiffness but also the morphology of the spherulites has an influence on the biodegradation properties. The highest biodegradability was observed for the copolyesters containing 5 and 10 mol% of fumarate units.     

Accelerated degradation behaviour of poly(?-caprolactone) via melt blending with poly(aspartic acid-co-lactide) (PAL)

Poly(?-caprolactone) (PCL) has many favourable attributes for tissue engineering scaffold applications. A major drawback, however, is its slow degradation rate, typically greater than 3 years. In this study PCL was melt blended with a small percentage of poly(aspartic acid-co-lactide) (PAL) and the degradation behaviour was evaluated in phosphate buffer solution (PBS) at 37 °C. The addition of PAL was found to significantly enhance the degradation profile of PCL. Subsequent degradation behaviour was investigated in terms of the polymer's mechanical properties, molecular weight (M_w), mass changes and thermal characteristics. The results indicate that the addition of PAL accelerates the degradation of PCL, with 20% mass loss recorded after just 7 months in vitro for samples containing 8 wt% PAL. The corresponding pure PCL samples exhibited no mass loss over the same time period. In vitro assessment of PCL and PCL/PAL composites in tissue culture medium in the absence of cells revealed stable pH readings with time. SEM studies of cell/biomaterial interactions demonstrated biocompatibility of C₃H₁₀T_1/2 cells with PCL and PCL/PAL composites at all concentrations of PAL additive.