Degradation of commercially important polyhydroxyalkanoates in tropical mangrove ecosystem

This paper presents the degradation trends of selected polyhydroxyalkanoate (PHA) films in a tropical mangrove environment. The biodegradability of homopolymer poly(3-hydroxybutyrate) [P(3HB)] and its co-polymers, poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyvalerate) [P(3HB-co-5 mol% 3HV)] and poly(3-hydroxybutyrate-co-5 mol% 3-hydroxyhexanoate) [P(3HB-co-5 mol% 3HHx)], was investigated along with P(3HB) films containing 38 wt% titanium dioxide (TiO₂) [P(3HB)-38 wt% TiO₂]. The degradation of these formulations was monitored for 8 weeks at three different zones in an intermediate mangrove compartment along Sungai Pinang, adjacent to a famous fishing village on south of Penang Island. The degradation rate was observed both on the surface and in the sediment and was expressed in percentage of weight loss. The microbial enumeration done using sediment from the different zones indicated similar colony-forming unit (CFU) counts even though differences were noticed in the degradation profile of the various films in the respective zones. The results obtained revealed that co-polymers disintegrated at similar or higher rate than the homopolymer, P(3HB). However, the incorporation of TiO₂ into PHB films caused the degradation rate of P(3HB)-38 wt% TiO₂ composite film to be far slower than all the other PHA films. The overall rate of degradation of all PHA films placed on the sediment surface was slower than those buried in the sediment. Microscopic analyses showed that the surface morphology of P(3HB-co-5 mol% 3HHx) was more porous compared to P(3HB) and P(3HB-co-5 mol% 3HV) films, which may be an important factor for its rapid degradation.     

Surface properties and enzymatic degradation of end-capped poly(l-lactide)

Surface properties and enzymatic degradation of poly(l-lactide) (PLLA) end-capped with hydrophobic dodecyl and dodecanoyl groups were investigated by means of advancing contact angle (θ_a) measurement, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The θ_a values of end-capped PLLA films were larger than those of non-end-capped PLLA films, suggesting that the hydrophobic dodecyl and dodecanoyl groups were segregated on the film surface. The weight changes of end-capped PLLA thin films during enzymatic degradation in the presence of proteinase K were monitored by using a QCM technique. The relatively fast weight loss of PLLA film occurred during first few hours of degradation, followed by a decrease in the erosion rate. The erosion rate of PLLA films at the initial stage of degradation was dependent on the chain-end structure of PLLA molecules, and the value decreased with an increase in the amount of hydrophobic functional groups. The surface morphologies of PLLA thin films before and after degradation were characterized by AFM. After the enzymatic degradation, the surface of non-end-capped PLLA films was blemished homogeneously. In contrast, the end-capped PLLA thin films were degraded heterogeneously by the enzyme, and many hollows were formed on the film surface. From these results, it has been concluded that the introduction of hydrophobic functional groups at the chain-ends of PLLA molecules depressed the erosion rate at the initial stage of enzymatic degradation.     

Bioconversion of Glycerine Pitch into a Novel Yellow-Pigmented P(3HB-co-4HB) Copolymer: Synergistic Effect of Ammonium Acetate and Polymer Characteristics

Glycerine pitch waste generated from oleochemical industry was exploited as a carbon source for poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) copolymer production by a novel, yellow-pigmented bacterium Cupriavidus sp. USMAHM13 to improve the economics of microbial polyhydroxyalkanoate production and to establish a feasible waste management approach. Medium optimization using response surface methodology through shake-flask fermentation had led to the accumulation of P(3HB-co-51%4HB) copolymer using a combination of glycerine pitch (10 g/l), 1,4-butanediol (8.14 g/l), and ammonium acetate (2.39 g/l). P(3HB-co-4HB) copolymers with 4HB monomer compositions ranged from 3 to 40 mol% were obtained through batch fermentation in a bioreactor using different concentrations of ammonium acetate. The copolymers exhibited a wide range of material properties depending on the monomer composition and type of carbon sources. P(3HB-co-40%4HB) was a typical random copolymer, whereas other P(3HB-co-4HB) produced were blend copolymers. Carotenoid pigment which was produced simultaneously with the polymer production was found to have negligible effect on the mechanical and thermal properties of the P(3HB-co-4HB) copolymer films.     

Current Advances towards 4-Hydroxybutyrate Containing Polyhydroxyalkanoates Production for Biomedical Applications

Polyhydroxyalkanoates (PHA) are polyesters having high promise in biomedical applications. Among different types of PHA, poly-4-hydroxybutyrate (P4HB) is the only polymer that has received FDA approval for medical applications. However, most PHA producing microorganisms lack the ability to synthesize P4HB or PHA comprising 4-hydroxybutyrate (4HB) monomer due to their absence of a 4HB monomer supplying pathway. Thus, most microorganisms require supplementation of 4HB precursors to synthesize 4HB polymers. However, usage of 4HB precursors incurs additional production cost. Therefore, researchers have adopted strategies to reduce the cost, such as utilizing low-cost substrate as well as constructing 4HB monomer supplying pathways in microorganisms. We herein summarize the biomedical applications of P4HB, the natural producers of 4HB polymer, and the various strategies that have been applied in producing 4HB polymers in non-4HB producing microorganisms. It is expected that the readers would gain a vivid idea on the different strategic developments in the field of 4HB polymer production.     

Biosynthesis and characterization of novel polyhydroxyalkanoate polymers with high elastic property by Cupriavidus necator PHB4 transformant

We attempted to synthesize novel polyhydroxyalkanoate (PHA) containing new 3-hydroxy-4-methylvalerate (3H4MV) monomer from the transformed strain of Cupriavidus necator PHB⁻4 harboring the PHA synthase gene of Chromobacterium sp. USM2 (phaC_Cs). Novel PHA containing SCL and MCL monomers were successfully synthesized from crude palm kernel oil (CPKO) and isocaproic acid. Results showed that P(3HB-co-1 mol% 3HV-co-3 mol% 3H4MV-co-18 mol% 3HHx) possessed higher thermal stability, higher elastomeric behavior at room temperature and higher ductility than the P(3HB-co-5 mol% 3HHx). The novel PHA film was found to possess an interesting rubber-like elasticity and flexibility property which has not been reported. The soil surface degradation study showed that the novel PHA film was degraded faster than the 3HB homopolymer and copolymer with 5 mol% of 3HHx.     

Biodegradation of a medium-chain-length polyhydroxyalkanoate in tropical river water

The medium-chain-length polyhydroxyalkanoate (PHA_MCL) produced by Pseudomonas putida PGA1 using saponified palm kernel oil as the carbon source could degrade readily in water taken from Kayu Ara River in Selangor, Malaysia. A weight loss of 71.3% of the PHA film occurred in 86 d. The pH of the river water medium fell from 7.5 (at d 0) to 4.7 (at d 86), and there was a net release of CO₂. In sterilized river water, the PHA film also lost weight and the pH of the water fell, but to lesser extents. The C8 monomer of the PHA was completely removed after 6 d of immersion in the river water, while the proportions of the other monomers (C10, C12, and C14) were reversed from that of the undegraded PHA. By contrast, the monomer composition of the PHA immersed in sterilized river water did not change significantly from that of the undegraded PHA. Scanning electron microscopy showed physical signs of degradation on the PHA film immersed in the river water, but the film immersed in sterilized river water was relatively unblemished. The results thus indicate that the PHA_MCL was degraded in tropical river water by biologic as well as nonbiologic means. A significant finding is that shorter-chain monomers were selectively removed throughout the entire PHA molecule, and this suggests enzymatic action.     

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.     

聚羟基烷酸酯酶降解动力学研究

研究了羟基丁酸 羟基戊酸共聚物 (PHBV)在脂肪酶中的降解行为 ,用滴定法测定降解速度并进行酶促反应动力学研究 .探讨了降解速度与酶浓度和底物浓度的数学关系和Michaelis Menten常数 ,从实验上和理论上证实了PHBV的物理形态和几何尺寸对酶降解过程的影响 ,以及实验数据与非均相动力学模型的拟合     

Cationic wood cellulose films with high strength and bacterial anti-adhesive properties

In this work, periodate oxidized birch wood pulp and microfibrillated cellulose (MFC) were cationized using Girard’s reagent T or aminoguanidine. Cationic celluloses were used to obtain films via solvent-casting method, and the effects of the cationization route and the cellulose fiber source on the properties of the films were studied. Thermal and optical properties of the films were measured using differential scanning calorimetry and UV–Vis spectrometry, and the morphology of the films was examined using an optical microscope and a field emission scanning electron microscope. Bacterial anti-adhesive properties of the films were also studied using a modified leaf print method and against Staphylococcus aureus and Escherichia coli. Both cationizing agents exhibited similar reactivity with periodate oxidized celluloses, however, MFC had significantly higher reactivity compared to birch pulp. The films with high tensile strength (39.1–45.3 MPa) and modulus (3.5–7.3 GPa) were obtained from cationized birch pulp, aminoguanidine modification producing a film with slightly better mechanical properties. Modulus of the films was significantly increased (up to 14.0 GPa) when MFC was used as a cellulose fiber source. Compared to the unmodified MFC films, the cationic MFC films were less porous and significantly more transparent; however, they had slightly lower tensile strength values. It was found that aminoguanidine modified celluloses had no culturable bacteria on its surface and also exhibited resistance to microbial degradation, whereas there were culturable bacteria on the surface of Girard’s reagent modified films and they were partially degraded by the bacteria.     

Influence of Teflon Substrate on Crystallization and Enzymatic Degradation of Polymorphic Poly（butylene adipate）

Oriented and non-oriented Teflon films, which were found to have the same crystalline structure, but different surface morphologies, were used to sandwich poly(butylene adipate)(PBA) films during isothermal crystallization. It was found that both the Teflon surface structure and the PBA polymorphic structure are the determining factors to induce epitaxial crystallization. The oriented Teflon film was able to induce epitaxial crystallization of PBA α crystal, while the non-oriented Teflon did not induce any epitaxial crystallization of PBA. Epitaxial crystallization did not occurred for PBA β crystals between neither the oriented nor the non-oriented Teflon films. The enzymatic degradation rate of PBA films was not determined by the epitaxial crystallization, in fact it was still dependent on the polymorphic crystal structure of PBA. The morphological changes of PBA films after enzymatic degradation confirmed again that the epitaxial crystallization only occurred for the PBA film with α crystal structure which was produced by being sandwiched between oriented Teflon films, and it happened only on the surface of PBA films.     

Enhancement of Stress Tolerance in the Polyhydroxyalkanoate Producers without Mobilization of the Accumulated Granules

Poly(3-hydroxybutyrate) [P(3HB)], a polymer belonging to the polyhydroxyalkanoate (PHA) family, is accumulated by numerous bacteria as carbon and energy storage material. The mobilization of accumulated P(3HB) is associated with increased stress and starvation tolerance. However, the potential function of accumulated copolymer such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] remained unknown. In this study, Delftia acidovorans DS 17 was used to evaluate the contributions of P(3HB) and P(3HB-co-3HV) granules during simulated exogenous carbon deprivation on cell survival by transferring cells with PHAs to carbon-free mineral salt medium supplemented with 1 % (w/v) nitrogen source. By mobilizing the intracellular P(3HB) and P(3HB-co-3HV) at 11 and 40 mol% 3HV compositions, the cells survived starvation. Surprisingly, D. acidovorans containing P(3HB-co-94 mol% 3HV) also survived although the mobilization was not as effective. Similarly, recombinant Escherichia coli pGEM-T::phbCAB _Cn (harboring the PHA biosynthesis genes of Cupriavidus necator) containing P(3HB) granules had a higher viable cell counts compared to those without P(3HB) granules but without any P(3HB) mobilization when exposed to oxidative stress by photoactivated titanium dioxide. This study provided strong evidence that enhancement of stress tolerance in PHA producers can be achieved without mobilization of the previously accumulated granules. Instead, PHA biosynthesis may improve bacterial survival via multiple mechanisms.     

Degradation of medium-chain-length polyhydroxyalkanoates in tropical forest and mangrove soils

Bacterial polyhydroxyalkanoates (PHAs) are perceived to be a suitable alternative to petrochemical plastics because they have similar material properties, are environmentally degradable, and are produced from renewable resources. In this study, the in situ degradation of medium-chain-length PHA (PHA_MCL) films in tropical forest and mangrove soils was assessed. The PHA_MCL was produced by Pseudomonas putida PGA1 using saponified palm kernel oil (SPKO) as the carbon source. After 112 d of burial, there was 16.7% reduction in gross weight of the films buried in acidic forest soil (FS), 3.0% in the ones buried in alkaline forest soil by the side of a stream (FSst) and 4.5% in those buried in mangrove soil (MS). There was a slight decrease in molecular weight for the films buried in FS but not for the films buried in FSst and in MS. However, no changes were observed for the melting temperature, glass transition temperature, monomer compositions, structure, and functional group analyses of the films from any of the burial sites during the test period. This means that the integral properties of the films were maintained during that period and degradation was by surface erosion. Scanning electron microscopy of the films from the three sites revealed holes on the film surfaces which could be attributed to attack by microorganisms and bigger organisms such as detritivores. For comparison purposes, films of polyhydroxybutyrate (PHB), a short-chain-length PHA, and polyethylene (PE) were buried together with the PHA_MCL films in all three sites. The PHB films disintegrated completely in MS and lost 73.5% of their initial weight in FSst, but only 4.6% in FS suggesting that water movement played a major role in breaking up the brittle PHB films. The PE films did not register any weight loss in any of the test sites.     

Degradation behaviors of polyester monolayers at the air/water interface: Alkaline and enzymatic degradations

The degradation kinetics of Langmuir monolayer films of a series of biodegradable polyesters has been studied to investigate the effect of degradation medium, alkalinity and enzymes. The degradation behavior of polyester monolayers strongly depended on both degradation medium and surface pressure. As the surface pressure was increased, the degradation rates of poly(l-lactide) (PLLA) and poly[(R)-3-hydroxybutyrate] (P(3HB)) increased in both degradation media. When monolayers were exposed to an alkaline subphase, the degradation of PLLA monolayers occurred at relatively low surface pressures; the PLLA monolayers were hydrolyzed at pH 10.5 regardless of surface pressure, while the alkaline degradation of P(3HB) monolayer occurred over a constant surface pressure of 7 mN/m at pH 11.8. These results have been explained by the difference in hydrophilic/hydrophobic balance of the polymers; PLLA is more hydrophilic than P(3HB). In contrast, the enzymatic degradations of both polymer monolayers occurred at higher constant surface pressures than those of the alkaline treatment; 7 mN/m for PLLA and 10 mN/m for P(3HB). This behavior was attributed to the enzymes being much larger than the alkaline ions: the enzymes need a larger contact area with the submerged monolayers to be activated.     

Studies on the Microbial Synthesis and Characterization of Polyhydroxyalkanoates Containing 4-Hydroxyvalerate Using γ-Valerolactone

In this study, the ability of Cupriavidus sp. USMAA2-4 to synthesize polyhydroxyalkanoates (PHA) containing 4-hydroxyvalerate monomer (4HV) was studied through one-stage cultivation using γ-valerolactone as the carbon precursor. The presence of 4HV monomer unit in the polymer was detected through gas chromatography analysis, proving the capability of this wild strain bacterium to produce poly(3-hydrxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) [P(3HB-co-3HV-co-4HV)] terpolymer. Existence of a 4HV monomer unit in the PHA produced was further confirmed through ¹³C and ¹H NMR analysis. P(3HB-co-88 % 3HV-co-1 % 4HV) terpolymer with the highest PHA content of 63 wt% was obtained through combination of 0.14 wt% C of γ-valerolactone with 0.42 wt% C of oleic acid. Various compositions of P(3HB-co-3HV-co-4HV) terpolymer with 3HV and 4HV compositions ranging from 11 to 94 mol% and from 1 to 4 mol%, respectively, were acquired by manipulating γ-valerolactone and oleic acid concentrations. The molecular weight and the thermal and mechanical properties of four different compositions of terpolymers—P(3HB-co-91 % 3HV-co-1 % 4HV), P(3HB-co-55 % 3HV-co-2 % 4HV), P(3HB-co-27 % 3HV-co-2 % 4HV), and P(3HB-co-9 % 3HV-co-1 % 4HV)—were characterized. Among these terpolymers, P(3HB-co-27 % 3HV-co-2 % 4HV) terpolymer with a molecular weight of 5.7 (10⁵ Da) exhibited the highest elongation to break (264 %). The monomer unit compositional distributions of these terpolymers were investigated through acetone–water fractionation analysis. The results suggested that these produced terpolymers had broad 3HV compositional distribution and narrow 4HV compositional distribution.     

Characteristic Interactions between Poly(hydroxybutyrate) Depolymerase and Poly[(R)‐3‐hydroxybutyrate] Film Studied by a Quartz Crystal Microbalance

Enzymatic degradation of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) film by the poly(hydroxybutyrate) (PHB) depolymerase from Ralstonia picketti T1 was studied in 0.01 M phosphate buffer solution (pH 7.4) at 37 °C by using a quartz crystal microbalance (QCM) technique. Enzymatic degradation of P(3HB) film was quantitatively followed by QCM as a positive frequency shift. While, the amount of depolymerases adsorbed on the film could be evaluated as a negative frequency shift by using a mutant enzyme which had no hydrolytic activity in a catalytic site. The degradation rate increased with enzyme concentration to reach a maximum value at 1.0 μg · mL^?1, and then the rate decreased at higher enzyme concentration. This enzyme concentration dependence could be quantitatively explained in terms of a change of coverage of the film surface by the adsorbed enzyme. When the wild‐type enzyme solution in a QCM cell was replaced with the mutant enzyme solution in the middle of the reaction, the degradation rate was reduced markedly, indicating that the wild‐type enzyme adsorbed on the P(3HB) surface is easily substituted by the mutant enzyme in the solution. On the other hand, replacement of the wild‐type enzyme solution with other proteins or buffer solutions did not affect the degradation rate at all, suggesting that the adsorbed enzyme was not desorbed from the film surface. Thus, the adsorbed PHB depolymerase is released from the P(3HB) surface only by interaction with the same depolymerase in solution.

Time courses of frequency changes (ΔF) or weight changes (Δw) observed during enzymatic degradation of P(3HB) film by PHB depolymerase from R. picketti T1 at 37 °C.     

Structural and optical properties of TiO2 thin films prepared by spin coating

Transparent semiconducting thin films of titanium oxide (TiO₂) were deposited on glass substrates by the sol–gel method and spin-coating technique. The physical properties of the prepared films were studied as a function of the number of spun-cast layers. The microstructure and surface morphology of the TiO₂ films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), with respect to the film thickness. The XRD analysis reveals that the films are polycrystalline with an anatase crystal structure and a preferred grain orientation in the (101) direction. The morphological properties were investigated by AFM, which shows a porous morphology structure for the films. The optical properties of the films were characterized by UV–Visible spectrophotometry, which shows that the films are highly transparent in the visible region and their transparency is slightly influenced by the film thickness, with an average value above 80 %. The dependence of the refractive index (n), extinction coefficient (k), and absorption coefficient (α) of the films on the wavelength was investigated. A shift in the optical band gap energy of the films from 3.75 to 3.54 eV, as a function of the film thickness, has been observed.     

Enzymatic transformation of bacterial polyhydroxyalkanoates into repolymerizable oligomers directed towards chemical recycling

The enzymatic transformation into an oligomer was carried out with the objective of developing the chemical recycling of bacterial polyesters. Poly(R-3-hydroxyalkanoate)s (PHAs), such as poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyhexanoate)] and poly[(R-3-hydroxybutyrate)-co-12%(R-3-hydroxyvalerate)], were degraded by granulated Candida antarctica lipase B immobilized on hydrophilic silica (lipase GCA) in a diluted organic solvent at 70 degrees C. The degradation products were cyclic oligomers having a molecular weight of a few hundreds. The obtained cyclic oligomer was readily repolymerized by the same lipase (lipase GCA) to produce the corresponding polyester in a concentrated solution. The cyclic oligomer was copolymerized with epsilon-caprolactone using lipase to produce the corresponding terpolymers having an Mw of 21,000. This is the first example of the enzymatic chemical recycling of bacterial PHAs using lipase. Poly(R-3-hydroxybutyrate) [P(3HB)] was also degraded into the linear-type R-3HB monomer to trimer by P(3HB)-depolymerase (PHBDP) in phosphate buffer at 37 degrees C. The degradation using PHBDP required a longer reaction time compared with the lipase-catalyzed degradation in organic solvent. The monomer composition of the oligomer depended on the origin of the PHBDP. The R-3HB monomer was predominately produced by PHBDP from Pseudomonas stutzeri, while the R-3HB dimer was produced by PHBDP from Alcaligenes faecalis T1. Repolymerization of these oligomers by lipase in concentrated organic solvent produced a relatively low-molecular-weight P(3HB) (e.g., Mw=2,000). Degradation of P(3HB) by lipase in organic solvent into repolymerizable cyclic oligomer and degradation of P(3HB) by PHBDP in buffer into hydroxy acid type R-3HB dimer.     

Controlled enzymatic degradation of poly(?-caprolactone)-based copolymers in the presence of porcine pancreatic lipase

Poly(?-caprolactone) (PCL) has been extensively studied for biomedical use due to its outstanding biocompatibility. Well-defined random and block copolymers based on PCL such as poly(?-caprolactone-r-2,2-dimethyltrimethylene carbonate) (PCD), poly[(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)-b-PEG-b-(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (PECD) and poly[MPEG-b-(?-caprolactone-r-2,2-dimethyltrimethylene carbonate)] (MPECD) containing 5.0-8.5 mol% 2,2-dimethyltrimethylene carbonate (DTC) and 15.9-18.3 mol% polyethylene glycol (PEG) or polyethylene glycol monomethyl ether (MPEG) have been synthesized by using lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) as catalyst. Their crystallization properties, thermal behaviors, hydrophilicities and degradation properties depend on the tunable microstructures and morphologies. It is found for the first time that porcine pancreatic lipase (PP lipase) can effectively catalyze the degradation of PCD electrospun mats (EMs) with 92.0% weight loss within 7 days while it shows no detectable effect on PCL EMs. Surface erosion mechanism is proposed in the enzymatic degradation systems, and the high proportion of amorphous domain of PCD contributes to its fast degradation rate according to the degradation product analyses. The enzymatic degradation rates of PCD EMs with porous structures and huge surface areas are higher than those of compression molding films (CMFs). Introducing PEG segment improves the hydrophilicity of PCD but decreases the degradation rate. A PEG segment enrichment process on the surface is addressed, which prevents the contact of PP lipase with PCD segments in the PEG-involved electrospun fiber. PECD and MPECD exhibit different mechanical strengths and contact angles, but similar degradation profiles. This study provides a practical example for tunable biodegradation of polyesters by designing the materials' bulk structures and/or surface morphologies.     

Rapid preparation of smooth nanocellulose films using spray coating

Spraying of nanocellulose (NC) on a solid surface to prepare films is an alternative technique to vacuum filtration, which requires a long drainage time and produces films which can sometimes be difficult to separate from the filter. This letter reports a rapid preparation technique for nano-cellulose films using a bench scale system spray coating nanocellulose suspension onto stainless steel plates. After spraying NC suspension onto a smooth steel plate travelling on a constant velocity conveyor, the films can be dried directly on the plates using standard laboratory procedures, saving processing time and effort. By adjusting the suspension consistency, we were able to reproducibly make films with a basis weight ranging from 52.8 ± 7.4 to 193.1 ± 3.4 g/m² when spraying on to a plate moving at a velocity of 0.32 cm/s. The operator preparation time for the nanocellulose film was 1 min, independent of the sample basis weight, which compares to production times reported in the literature of 10 min using filtration techniques. The films made by spray coating showed higher thickness, but comparable uniformity, to those made by vacuum filtration. Optical profilometry measurements showed that over a 1 cm × 1 cm inspection area that the surface roughness (RMS) of the NC film is only 389 nm on the spray coated side in contact with the steel plates, compared to 2087 nm on the outside surface. Thus, the reduction in preparation time for producing the nanocellulose film recommends this spray coating technique as a rapid and flexible method to produce NC films at the laboratory scale.     

Degradation behaviour of PCL/PEO/PCL and PCL/PEO block copolymers under controlled hydrolytic,enzymatic and composting conditions

Short-term hydrolytic and enzymatic degradation of poly(ε-caprolactone) (PCL), one series of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers, with a low content of hydrophilic PEO segments is presented. The effect of the introduction of PEO as the central or lateral segment in the PCL chain on copolymer hydrolysis and biodegradation properties was investigated. FTIR results revealed higher hydrolytic degradation susceptibility of diblock copolymers due to a higher hydrophilicity compared to PCL and triblock copolymers. Enzymatic degradation was tested using cell-free extracts of Pseudomonas aeruginosa PAO1, for two weeks by following the weight loss, changes in surface roughness, and changes in carbonyl and crystallinity index. The results confirmed that all samples underwent enzymatic degradation through surface erosion which was accompanied with a decrease in molecular weights. Diblock copolymers showed significantly higher weight loss and decrease in molecular weight in comparison to PCL itself and triblock copolymers. AFM analysis confirmed significant surface erosion and increase in RMS values. In addition, biodegradation of polymer films was tested in compost model system at 37 °C, where an effective degradation of block copolymers was observed.