Preparation of porous ultra-fine poly(vinyl cinnamate) fibers

In this study, a new method of preparing porous ultra-fine fibers via photo-crosslinking was developed. Ultra-fine poly(vinyl cinnamate)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PVCi/PHBV) blend fibers were electrospun and then the PVCi was photo-crosslinked by UV irradiation. PVCi and PHBV were immiscible and the phase separation proceeded during the electrospinning process. After the photo-crosslinking of PVCi, PHBV was extracted from the blend fibers with chloroform. The average pore sizes in the remaining ultra-fine PVCi fibers were increased with increasing the content of PHBV in the ultra-fine PVCi/PHBV fibers.     

Processing and characterization of solid and microcellular PHBV/PBAT blend and its RWF/nanoclay composites

Solid and microcellular components made of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly (butylene adipate-co-terephthalate) (PBAT) blend (weight ratio of PHBV:PBAT = 30:70), recycled wood fiber (RWF), and nanoclay (NC) were prepared via a conventional and microcellular-injection molding process, respectively. Morphology, thermal properties, and mechanical properties were investigated. The addition of 10% RWF (both untreated and silane-treated) reduced the cell size and increased the cell density of the microcellular components. Also, the addition of 10% RWF (both untreated and silane-treated) generally increased the specific Young’s modulus and tensile strength, but decreased the specific toughness and strain-at-break in both solid and microcellular components. Moreover, unlike the neat PHBV/PBAT blend, microcellular PHBV/PBAT/RWF (both untreated and silane-treated) composites showed higher specific toughness and strain-at-break compared to their solid counterparts. In addition, higher specific toughness and strain-at-break was observed in the PHBV/PBAT/untreated-RWF composite compared with the PHBV/PBAT/silane-treated RWF composite, particularly in the microcellular components. The degree of PHBV crystallinity increased significantly in both solid and microcellular PHBV/PBAT/RWF composites although the degree of PHBV crystallinity in the solid components was slightly higher than that of their microcellular counterparts. The effects of adding 2% nanoclay on the properties of the PHBV/PBAT/silane-treated-RWF composite were also investigated. The nanoclays exhibited an intercalated structure in the composites based on XRD analysis and did not induce significant changes in the cell morphology and mechanical properties of the PHBV/PBAT/silane-treated-RWF composite. However, it did improve its thermal stability.     

Improving the interfacial adhesion in a new renewable resource-based biocomposites from biofuel coproduct and biodegradable plastic

Biocomposites of a biopolymer and the coproduct of corn bioethanol industry, dried distillers’ grains with solubles (DDGS), were produced by reactive melt extrusion and injection molding. The biopolymer matrix was a blend of polyhydroxy(butyrate-co-valrerate), PHBV, and poly(butylene adipate-co-terphthalate), PBAT. The effect of compatibilizer, polymeric methylene diphenyl diisocyanate (PMDI), and corn oil lubricant was studied. The change in melt processing force suggested the occurrence of chemical reactions during the processing. This hypothesis was further investigated by infrared spectroscopy by which the formation of urethane and urea bonds between DDGS and polymeric matrix was approved. Dynamic mechanical analysis confirmed the occurrence of crosslinks at PBAT–PHBV interface showing that the tan δ curves for PBAT and PHBV of the matrix shifted slightly towards each other. Moreover, the calculated parameter of interaction, A, from tan δ curves admitted the stronger bond at the DDGS–matrix interface as a result of addition of PMDI compatibilizer. Also, scanning electron microscopy images revealed improved interfacial adhesion at the DDGS–matrix interface as well as PBAT–PHBV interface within the matrix itself. The obtained crosslinked interfaces resulted in improvement in the strength, modulus, and elongation-at-break of biocomposites. Moreover, a synergism of PMDI and corn oil effects led to a dramatic improvement in impact strength of this biocomposite system so that the respective value for the prepared DDGS biocomposite increased from 75 to 212 J/m with addition of 1 % of PMDI and 3 % of corn oil.     

Temperature-sensitivity and cell biocompatibility of freeze-dried nanocomposite hydrogels incorporated with biodegradable PHBV

The structure, morphology, thermal behaviors and cytotoxicity of novel hydrogels, composed of poly(N-isopropylacrylamide)(PNIPAM) and biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) under nanoclay hectorite “Laponite XLG” severed as physical cross-linker, were characterized by X-ray diffraction, scanning electron microscopy, gravimetric method, differential scanning calorimetry, and cell culture experiments. It was found that, due to the introduction of hydrophobic PHBV, the homogeneity of interior pore in the pure PNIPAM nanocomposite hydrogel was disrupted, the transparency and swelling degree gradually decreased. Although the weight ratio between PHBV and NIPAM increased from 5 to 40 wt.%, the volume phase transition temperature (VPTTs) of hydrogel were not altered compared with the pure PNIPAM nanocomposite hydrogel. No matter what PHBV content, the PHBV/PNIPAM/Hectorite hydrogels always exhibit good stimuli-responsibility. In addition, human hepatoma cells(HepG2) adhesion and spreading on the surface of PHBV-based hydrogels was greatly improved than that of pure PNIPAM nanocomposite hydrogel at 37 °C due to the introduction of PHBV.     

可全生物降解PLA/PBAT/PHBV共混材料的结构与性能

为了得到刚性与韧性平衡的聚乳酸（PLA）基可生物降解共混材料,通过熔融共混挤出法制备了不同质量比的PLA/己二酸-对苯二甲酸-丁二酯共聚物（PBAT）/聚（3-羟基丁酸-co-羟基戊酸共聚酯（PHBV）可全生物降解共混材料,采用SEM、TG、DSC、毛细管流变仪和万能材料试验机对PLA/PBAT/PHBV共混材料的形态结构、热性能、流变性能和力学性能进行了研究。结果表明:PLA/PBAT/PHBV共混材料的热失重起始分解温度相对纯PHBV提高了45 ℃,热稳定性提高;共混体系中各组分的玻璃化转变温度与单一体系相比几乎无变化,PLA/PBAT/PHBV共混体系为完全不相容体系,同时PBAT和PHBV的加入阻碍了PLA的冷结晶;PLA/PBAT/PHBV 共混体系的共混形态呈“海-岛”分布,PBAT和PHBV均匀地分散于PLA基体中,相界面分明;随着PBAT含量增加,PLA/PBAT/PHBV共混材料熔体的流动性增加,温度变化对黏度的影响变大;PLA/PBAT/PHBV质量比为70/20/10的共混材料可在保留纯PLA 60%拉伸应力的同时,拉伸应变提高到纯PLA的2.6倍,韧性得到改善。所得结论表明PLA/PBAT/PHBV质量比为70/20/10的共混材料的综合力学性能较纯PLA好。      

Microparticles of poly(hydroxybutyrate-co-hydroxyvalerate) loaded with andiroba oil: Preparation and characterization

Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a biodegradable polyester, was used in the preparation of polymeric microparticles containing andiroba oil. Andiroba oil, extracted from the seeds of Carapa guianensis, has insecticide and medicinal properties. Microparticles of PHBV were prepared using o/w simple emulsion followed by solvent evaporation. The properties of these microparticles, such as encapsulation efficiency, and morphological aspects were investigated. Several characterization techniques were used: FTIR, XRD, DSC, TGA-DTA, SEM, and particle-size analysis. The efficiency of encapsulation of andiroba oil was determined by UV-spectroscopy. The results confirmed that PHBV microspheres containing andiroba oil were obtained.     

Processing conditions and characterization of novel electrospun poly (3-hydroxybutyrate-co-hydroxyvalerate)/chitosan blend fibers

Novel hybrid fibrous membranes with potential application on the biomedical field were successfully developed via electrospinning of blend solutions of two biocompatible and biodegradable polymers, poly (3-hydroxybutyrate-co-hydroxyvalerate) [PHBV] and chitosan. The effect of solvent, using different proportions of trifluoracetic acid (TFA) and 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP), PHBV/chitosan ratio, and chitosan molecular weight on solution spinnability, fiber morphology and size, and in vitro degradation were investigated. Continuous nanofiber structures were obtained from pristine PHBV to a PHBV/chitosan ratio of 2:3 (w/w), at 10% (w/v) total polymer concentration. In general, main fiber average diameters increased as chitosan content and molecular weight increased and decreased with the decrease of HFIP content in the solvent. In vitro dissolution tests revealed that the hybrid fibers show much higher degradation rates than the neat PHBV.     

Effect of lipase treatment on the biocompatibility of microbial polyhydroxyalkanoates

Films made from microbial polyesters polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) were treated by lipases and NaOH solution. The change of the polyester biocompatibility was evaluated by inoculating mouse fibroblast cell line L929 on films of PHB, PHBHHx and their blends. Polylactic acid (PLA) was used as a control. It was found that untreated PHB and PLA films gave a poor support to the growth of L929 cells, viable cell density ranged from 0.1×10⁴ to 0.7×10⁴ per ml only. While films of pure PHBHHx and PHB blended with PHBHHx showed improved biocompatibility, viable cell density observed increased from 9.6×10² to 6×10⁴ on blended films of PHB/PHBHHx in ratios of 0.9/0.1 to 0/1, respectively. This result showed PHBHHx has a better biocompatibility compared with PHB. Films of PHB, PLA and the blends treated with lipases and 1 N NaOH, respectively, showed an improved ability to support cell growth. Biocompatibility of PHB was approximately the same as PLA after the treatment, while PHBHHx and its dominant blends showed improved biocompatibility compared with PLA. The sensitivity of the treatments was reduced when PHBHHx content increased in the PHB/PHBHHx blends. All three lipase treatments demonstrated more biocompatibility increase on all the films compared with the results of NaOH treatment. Scanning electron microscopy showed that PHB films changed its surface from multi-porous to rough non-porous after the lipase or NaOH treatment. While PHBHHx films showed little change after these treatments. The results showed that the polyester surface morphology played an important role in affecting cell attachment and growth on these materials.     

Influence of ethylene glycol vapor annealing on structure and property of wet-spun PVA/PEDOT:PSS blend fiber

In this study, blend fibers composed of poly(vinyl alcohol) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) were prepared via wet-spinning technology. Ethylene glycol (EG) vapor annealing was employed to improve the electrical conductivity and tensile properties of blend fibers. The effects of EG vapor annealing on structures and properties of blend fibers were investigated in detail by analyzing the changes in chemical constituent and structure, molecular structure, surface morphology, surface chemical composition, electrical conductivity, and tensile properties. FTIR spectroscopy indicates that EG vapor annealing does not change the chemical constituent and structure of blend fibers. Raman spectroscopy shows that vapor annealing leads to conformational changes of PEDOT chains from benzoid structure to quinoid structure. AFM and SEM images show that surface morphology of blend fibers become smoother after vapor annealing. XPS measurement shows that EG vapor annealing induces significant phase separation between PEDOT and PSS, forming an enriched PSS layer on the surface of blend fibers, thus leading to a thinner insulating PSS layer between PEDOT grains. This conformational change is beneficial to improve the electrical conductivity of blend fibers. The resultant blend fiber reached conductivity up to 20.4 S cm^?1. The mechanical properties of blend fibers were also improved by EG vapor annealing, with the Young’s modulus and tensile strength increasing from 3.6 GPa and 112 MPa to 4.4 GPa and 132.7 MPa, respectively.     

A novel PHBV/HA microsphere releasing system loaded with alendronate

Microspheres of poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) incorporated with hydroxyapatite (HA) and loaded with alendronate (AL), an osteoporosis preventing drugs, were prepared by single emulsion technique. Several methods were used to evaluate this novel drug carrier microsphere system (referred as PHBV/HA–AL). Fourier transform infrared (FTIR) was used to evaluate the enwrapping of HA and the X-ray diffraction (XRD) analysis further confirmed the success. The morphology of PHBV/HA–AL microspheres was observed by scanning electron microscope (SEM), showing rough surface with HA particles enwrapped in the PHBV matrix. The in vitro drug releasing profile of PHBV/HA–AL system was investigated in a 26-day period. There is a sustained releasing pattern after a slight burst release during the first few days. Additionally, rabbit mesenchymal stem cells (MSCs) were used to evaluate the cytotoxicity of the PHBV/HA–AL composites. This controlled release system can well support the proliferation of MSCs. The novel PHBV/HA–AL controlled release system is promising for bone repair therapy.     

MFC-structured biodegradable poly(l-lactide)/poly(butylene adipate-co-terephatalate) blends with improved mechanical and barrier properties

Both polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are biodegradable polymers. They are thermoplastics which can be processed using conventional polymer processing methods. In this study, microfibrillar-reinforced composites (MFC) based on PLA/PBAT (PLA/Ecoflex^®) blends in different weight ratios were prepared under industry-relevant conditions by melt extrusion followed by continuous cold drawing of the extrudates. Strip-like specimens (films) and plates (laminates) of the drawn blends were prepared by compression molding (CM) at processing temperature above the melting temperature (T _m) of PBAT, but below T _m of PLA. SEM and WAXS observations show that the extruded blend components are isotropic, but become highly oriented after drawing, and they are converted into MFC-structured polymer–polymer composites after CM. An effect of PLA microfibrils on the non-isothermal crystallization of the Ecoflex during cooling from the melt, associated with the formation of crystalline regions of the matrix around the fibrils, was observed. Depending on the blend composition, the compression-molded samples possess a 3- to 7-time higher tensile strength as well as a 15–30 higher modulus than the neat Ecoflex. In addition, the MFC-structured plates exhibited superior barrier properties compared to the neat Ecoflex, e.g., the oxygen permeability decreased by up to 5 times.     

Effect of composition ratio on the thermal and physical properties of semicrystalline PLA/PHB-HHx composites

In this study, composites of semicrystalline, biodegradable polylactide (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHB-HHx) were prepared by direct melt compounding. The physical and thermal properties of the composites were investigated as a function of the composition ratio. Differential scanning calorimetry analysis indicated that PLA and PHB-HHx formed immiscible composites over the observed range of composition. The crystallization of PLA was gradually suppressed by increasing proportions of PHB-HHx. Dynamic mechanical analysis results confirmed that the innate ductility of PHB-HHX and its inhibiting effect on PLA crystallization improved the stiffness of the composite compared to those of neat PLA. The infrared spectra of the immiscible PLA/PHB-HHx composites at two crystallization temperatures (30 °C, 130 °C) were obtained and presented. At 30 °C, PHB-HHx existed as crystalline domains in the PLA matrix, while, amorphous phase of molten PHB-HHx was diffused within the crystalline phase of PLA at 130 °C. The interaction between PHB-HHX and PLA could not be elucidated from the temperature data. Mechanical tests showed that the addition of PHB-HHx improves ductility of PLA/PHB-HHx composite. Morphological analysis revealed that small proportions of PHB-HHx exhibited less tendency to aggregate, which resulted in greater plastic deformation and improved toughness. From this study, PLA blended with small portions of PHB-HHx may further expand the use of bio-friendly resources in a variety of applications such as flexible films, food packaging and something like that.     

Osteointegration of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds incorporated with violacein

This work reports on the production and in vivo evaluation of biodegradable scaffolds of poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) incorporated with violacein, an antibiotic and antitumoral agent. PHBV produced in a bioreactor by Chromobacterium violaceum was pressed and partially sintered to produce scaffolds with 3 mm of diameter and 3 mm of height. The scaffolds were microstructurally characterized and exhibited suitable micromorphology for bone ingrowth. The PHBV-violacein scaffolds were implanted in femur of Wistar rats, extracted and analyzed after 30 and 60 days of surgery. Histological evaluation revealed that no inflammatory reaction occurred and new bone tissue was formed in the implant. The results indicated that PHBVs with violacein are potential candidates for application in regenerative bone tissue engineering.     

Tetracycline hydrochloride (TCH)-loaded drug carrier based on PLA:PCL nanofibre mats: experimental characterisation and release kinetics modelling

The experimental characterisation of electrospun poly(lactic acid) (PLA):poly(ε-caprolactone) (PCL) as drug carriers, at five blend ratios from 1:0, 3:1, 1:1, 1:3 and 0:1, was holistically investigated in terms of their morphological structures, crystallinity levels and thermal properties. A widely used antibiotic tetracycline hydrochloride (TCH) was loaded to prepared fibrous mats at TCH concentrations of 1 and 5 wt%. The additional TCH into PLA:PCL better facilitates the reduction of fibre diameter than polymer blends. Increasing the TCH concentration from 1 to 5 wt% was found to result in only a modest decrease in the crystallinity level, but a significant increase in the crystallisation temperature (T _c) for PLA within PLA:PCL blends. The infrared spectra of fibre mats confirm the successful TCH encapsulation into fibrous networks. The first order and Zeng models for drug release kinetics were in better agreement with experimental release data, indicating the release acceleration of TCH with increasing its concentration. In a typical case of PLA:PCL (1:1) loaded with 5 wt% TCH, the fibre mats apparently demonstrate more wrinkled and floppy structures and increased fibre diameters and decreased inter-fibrous spaces after 7-day in vitro fibre degradation, as opposed to those obtained after 3-h degradation.     

Solution blow spinning: parameters optimization and effects on the properties of nanofibers from poly(lactic acid)/dimethyl carbonate solutions

Solution blow spinning (SBS) is a process to produce non-woven fiber sheets with high porosity and an extremely large amount of surface area. In this study, a Box–Behnken experimental design (BBD) was used to optimize the processing parameters for the production of nanofibers from polymer solutions consisting of poly(lactic acid) (PLA) dissolved in dimethyl carbonate. In addition, a comparative study between SBS fibers and cast film was performed to verify the influence of the SBS process on the crystallinity and thermal properties of PLA. The PLA concentration in polymer solutions was the most significant parameter affecting fiber diameter. The BBD analysis revealed that small diameter fibers were best obtained by a combination of 8 % w/v PLA concentration, 80 psi air pressure, and a feed rate of 50 µL min^?1. The comparative study showed that both the SBS and the film casting processes increased the PLA crystallinity. However, the PLA films had a higher degree of crystallinity compared with the fibers made by the SBS process (39 and 17 %, respectively), which was attributed to the high shear created at the SBS nozzle inducing orientation and chain alignment. During the fiber formation, crystals formed with varied morphology including the α′-crystals, which have a less ordered structure and lower thermal stability compared to the α-crystals. The lower thermal stability of SBS fibers compared to the films can be explained by the lower degree of crystallinity and also by the higher surface area which can accelerate the weight loss process.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

A new nanofiber fabrication technique based on coaxial electrospinning

In tissue engineering, nanofibrous scaffolds can achieve better biological responses than microfibrous scaffolds and electrospinning is a common method for producing fibrous scaffolds. However, not all biopolymers can be made into nanofibers through conventional electrospinning. The current investigation developed an innovative nanofiber fabrication technique based on coaxial electrospinning and used poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) as an example for achieving nanofibers. For obtaining PHBV nanofibers, core-shell structured fibers were fabricated first via coaxial electrospinning, with PHBV being the core and chitosan being the shell. The chitosan shell was then removed by washing electrospun scaffolds with water, leading to the formation of nanofibrous PHBV scaffolds. The PHBV nanofiber diameter was affected by the inner polymer (i.e., PHBV) solution concentration during coaxial electrospinning, which can be explained in terms of the coaxial electrospinning process and polymer solution viscosity. Compared to the approach of using a conductivity-enhancing salt in polymer solution to produce polymer nanofibers, the new technique not only eliminates the biocompatibility concerns but also provides a more effective way of reducing fiber diameters to the nano-size range.     

Characterization of spray-coating methods for conjugated polymer blend thin films

We examine the characteristics and functionality of conjugated polymer thin films, based on blends of poly(9,9-dioctylfluorene-2,7-diyl-co-bis-N,NN′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-2,7-diyl-co-benzothiadiazole) (F8BT), using a spray-coating deposition technique suitable for large areas. The morphological properties of these blend films are studied in detail by atomic force microscopy (AFM) methods, showing that favourable results, in terms of layer deposition rate and uniformity, can be achieved using a 5:1 blend of o-dichlorobenzene and chlorobenzene as the solvent medium. A photoluminescence quenching efficiency of above 80 % is also observed in such blend films. As a feasibility study, prototypical photovoltaic devices exhibit open circuit voltages of up to 1.0 V under testing, and solar power conversion efficiencies in the 0.1–1 % order of magnitude; metrics which are comparable with those reported for spin-coated cells of the same active blend and device architecture.     

Crystallization kinetics of poly(hydroxybutyrate- co -hydroxyvalerate) and poly(dicyclohexylitaconate) PHBV/PDCHI blends: thermal properties and hydrolytic degradation

The influence of poly(dicyclohexylitaconate) (PDCHI) content, on the crystallization kinetics, thermal properties, and hydrolytic degradation of poly(hydroxybutyrate-co-hydroxyvalerate), PHBV, was studied. Irrespective of the blend composition, the calorimetric and FTIR spectroscopy analyses indicate that the blend components are immiscible. The kinetics of non-isothermal crystallization and melting behavior of PHBV were studied by differential scanning calorimetry (DSC) and examined using non-isothermal Avrami and Mo’s analyses. Based on Mo’s model, the PDCHI content has significant effect on the crystallization kinetics of PHBV matrix. Despite the immiscibility of these polymers, the amorphous polyvinyl ester could extensively control the rate of hydrolytic degradation.     

Crystallization behavior of poly(hydroxybytyrate-<Emphasis Type="Italic">co</Emphasis>-valerate) in model and bulk PHBV/kenaf fiber composites

The kinetics of non-isothermal crystallization and melting behavior of poly(hydrohybutyrate-co-valerate) (PHBV) in model, bulk and compatibilized (PHBV)/kenaf fiber composites were investigated using differential scanning calorimetry (DSC). Analysis of the non-isothermal crystallization data was carried out based on the Avrami and Mo’s models. Activation energies of the crystallization process were determined by the Kissinger approach, and were in the range between 41 and 48 kJ/mol for all investigated samples. It was shown that the kenaf fibers, as well as their content, do not affect significantly the crystallization kinetics of PHBV matrix. The results indicate that crystallization behavior of polymer resin in bulk composites is not affected by the melt processing, thus suggesting absence of degradation processes.