Micro construction of poly(epsilon-caprolactone)/poly(L-lactic acid) blend film by solution casting under microwave irradiation

The micro construction of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) blend films fabricated by solution casting under microwave irradiation was investigated by selective enzymatic degradation and scanning electron microscopy (SEM). The results were totally different from the blends obtained by conventional methods. The blend was more homogeneous and the PCL continuous phase more compact as no spherulites and tiny zone separation were observed from the film surface and no PCL network was observed inside the film, and the degradation of a PCL plank by Pseudomonas lipase was significantly retarded. The distributed PLLA micro spheres were enlarged and amorphous. The thermal behavior of the blend by microwave heating revealed that PCL and PLLA underwent a melting process, which induced the variations of the PCL phase and PLLA spheres. The weight loss caused by degradation of the PCL/PLLA blend obtained by conventional methods (B50c) is greater than that of the blend obtained by microwave methods (B50m), which reflects the change in morphology from a loose PCL network (B50c) to a dense PCL plank (B50m).     

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.     

Synthesis and properties of photocurable biodegradable multiblock copolymers based on poly(ε‐caprolactone) and poly(L‐lactide) segments

Photocurable biodegradable multiblock copolymers were synthesized from poly(ε‐caprolactone) (PCL) diol and poly(L ‐lactide) (PLLA) diol with 4,4′‐(adipoyldioxy)dicinnamic acid (CAC) dichloride as a chain extender derived from adipoyl chloride and 4‐hydroxycinnamic acid, and they were characterized with Fourier transform infrared and ¹H NMR spectroscopy, gel permeation chromatography, wide‐angle X‐ray diffraction, differential scanning calorimetry, and tensile tests. The copolymers were irradiated with a 400‐W high‐pressure mercury lamp from 30 min to 3 h to form a network structure in the absence of photoinitiators. The gel concentration increased with time, and a concentration of approximately 90% was obtained in 90–180 min for all the films. The photocuring hardly affected the crystallinity and melting temperature of the PCL segments but reduced the crystallinity of the PLLA segments. The mechanical properties, such as the tensile strength, modulus, and elongation, were significantly affected by the copolymer compositions and gel concentrations. Shape‐memory properties were determined with cyclic thermomechanical experiments. The CAC/PCL and CAC/PCL/PLLA (75/25) films photocured for 30–120 min showed good shape‐memory properties with strain fixity rates and recovery rates of approximately 100%. The formation of the network structure and the crystallization and melting of the PCL segments played very important roles for the typical shape‐memory properties. Finally, the degradation characteristics of these copolymers were investigated in a phosphate buffer solution at 37 °C with proteinase‐k and Pseudomonas cepacia lipase. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2426–2439, 2005     

Enzymatic chain scission kinetics of poly(epsilon-caprolactone) monolayers

The hydrolytic and enzymatic degradation behavior of poly(epsilon-caprolactone) (PCL) is investigated using the Langmuir monolayer technique, and an improved data acquisition and data reduction procedure is presented. Hydrolytic and enzymatic monolayer degradation experiments of PCL with various molecular weights by Pseudomonas cepacia lipase have been carried out to analyze the influence of subphase pH, subphase temperature, enzyme concentration, and the packing density of polymer chains on the degradation kinetics. The enzymatic monolayer degradation results in an exponential increase in the number of dissolved degradation fragments with increasing degradation time, which confirms random chain scission to be the dominant scission mechanism. The increase in the enzymatic scission rate constant with decreasing initial average molecular weight of the polymers is assigned to the influence of the area density of polar terminal groups on the substrate-enzyme complex formation.     

Enzymatic degradation of block copolymers obtained by sequential ring opening polymerization of l-lactide and ?-caprolactone

Copolymers of ?-caprolactone and l-lactide with different molar ratios were prepared via sequential ring opening polymerization (ROP) of both monomers. The resulting PCL-PLLA-PCL triblock copolymers were characterized by using NMR, SEC, DSC and XRD. One melting peak corresponding to the PCL block was detected, but the presence of PLLA decreased the crystallinity of PCL. Enzyme-catalyzed biodegradation of solution cast films was investigated at 37 °C in the presence of Pseudomonas lipase. It was observed that the PLLA component retarded the degradation of the block copolymer as compared to the PCL homopolymer. Therefore, the enzymatic degradation rate can be adjusted by varying the composition of the copolymers. ¹H NMR and SEC data showed no significant chemical composition or molecular weight changes during degradation, indicating that the degradation proceeded according to a surface erosion mechanism. ESEM confirmed surface erosion with appearance of a rugged morphology.     

A comparative analysis of mass losses of some aliphatic polyesters upon enzymatic degradation

Results of investigation of mass losses, geometrical surface structure changes and variations in crystallinity of poly(lactic acid) (PLA), poly(?-caprolactone) (PCL) and commercially available material (PHB) consisting of poly(3,4-hydroxybutyrate) and poly(lactic acid) are presented. These structural changes occurred due to degradation of these polymers in the presence of the following enzymes: proteinase K, protease, esterase or lipase. Independently of the enzyme type, the largest mass loss was found for PLA and the smallest for PHB. Thus, under the experimental conditions, the processes of enzymatic degradation proceeded most rapidly in PLA, more slowly in PCL, and the most slowly in PHB. It was also found that proteinase K caused the largest mass losses, protease caused smaller mass losses, and both esterase and lipase produced the least mass losses, while lipase did not bring about mass loss in PHB. Images of surfaces of individual samples, obtained by scanning electron microscopy (SEM), indirectly confirmed the results of the mass loss examination. Crystallinity of the studied polyesters increased with degradation in the presence of proteinase K and protease, while changes in the crystallinity due to esterase and lipase were not observed. The presented results illustrate well the relative susceptibilities of the individual polyesters toward degradation induced by various enzymes.     

Laser light-scattering studies of poly(caprolactone-b-ethylene oxide-b-caprolactone) nanoparticles and their enzymatic biodegradation

Water-insoluble triblock poly(caprolactone-b-ethylene oxide-b-caprolactone) (PCL-PEO-PCL) was micronized into narrowly distributed nanoparticles stable in water. Using a combination of static and dynamic laser light scattering (LLS), we characterized the resultant nanoparticles and studied their biodegradation in the presence of enzyme lipase PS. The results revealed that the biodegradation rate was mainly dependent on the enzyme concentration. The scattering intensity decreased as the degradation proceeded, but there was no change in size of the remaining nanoparticles, indicating that the degradation of each particle was fast and the enzyme consumed the nanoparticles individually. We also found that different copolymer compositions, i.e., different PCL–PEO molar ratios, led to different biodegradation rates. The pH and temperature dependence of the biodegradation rate were also studied. All results indicated that the biodegradation rate can be well controlled and the biodegradation essentially involves two processes: adsorption of lipase PS onto the nanoparticles, and enzymatic hydrolysis of the PCL blocks. The biomedical application of the enzymatic biodegradation of the copolymer nanoparticles is also envisioned. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3288–3293, 1999     

Synthesis and characterization of poly(L‐lactic acid)–poly(ε‐caprolactone) multiblock copolymers by melt polycondensation

An Erratum has been published for this article in J. Polym. Sci. Part A: Polym. Chem. (2004) 42(22) 5845 New multiblock copolymers derived from poly(L‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) were prepared with the coupling reaction between PLLA and PCL oligomers with ? NCO terminals. Fourier transform infrared (FTIR), ¹³C NMR, and differential scanning calorimetry (DSC) were used to characterize the copolymers and the results showed that PLLA and PCL were coupled by the reaction between ? NCO groups at the end of the PCL and ? OH (or ? COOH) groups at the end of the PLLA. DSC data indicated that the different compositions of PLLA and PCL had an influence on the thermal and crystallization properties including the glass‐transition temperature (T_g), melting temperature (T_M), crystallizing temperature (T_c), melting enthalpy (ΔH_m), crystallizing enthalpy (ΔH_c), and crystallinity. Gel permeation chromatography (GPC) was employed to study the effect of the composition of PLLA and PCL and reaction time on the molecular weight and the molecular weight distribution of the copolymers. The weight‐average molecular weight of PLLA–PCL multiblock copolymers was up to 180,000 at a composition of 60% PLLA and 40% PCL, whereas that of the homopolymer of PLLA was only 14,000. A polarized optical microscope was used to observe the crystalline morphology of copolymers; the results showed that all polymers exhibited a spherulitic morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5045–5053, 2004     

Enzymatic and chemical hydrolysis of poly(ethylene terephthalate) fabrics

Alkaline and enzymatic hydrolyzes of poly(ethylene terephthalate) fabrics (PET) were mechanistically compared based on released degradation products (HPLC‐UV‐RI) and changes in surface properties [hydrophilicity, cationic dyeing, X‐ray photoelectron spectroscopy (XPS)]. Enzymatic hydrolysis led to an increase in the amount of hydroxyl and carboxyl groups on the surface resulting in an enhanced water absorption and dyeability. Enzymes partially adsorbed to PET fabrics during hydrolysis were completely removed by subsequent extraction according to XPS analysis. In contrast to the enzyme treatment, alkaline hydrolysis did not lead to an increase of hydroxyl and acid groups according to XPS while both treatments caused a substantial increase in hydrophilicity and were more effective on amorphous fibers. Alkaline hydrolysis led to a greater increase in the K/S value after cationic dyeing due to enlarged surface area. Consequently, ESEM‐images demonstrated that alkaline treatment drastically affected the surface morphology of the polymer resulting in crater‐like structures of the fibers, whereas after enzymatic treatment the morphology of the fibers remained unchanged. To reach similar benefits in hydrophilicity, drastically higher amounts of degradation products were released during alkaline hydrolysis as also indicated by >6% weight loss compared to <1% after enzyme treatment. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6435–6443, 2008     

Characteristics of the biodegradability and physical properties of stereocomplexes between poly(L‐lactide) and poly(D‐lactide) copolymers

Random and block copolymerizations of L ‐ or D ‐lactide with ε‐caprolactone (CL) were performed with a novel anionic initiator, (C₅Me₅)₂SmMe(THF), and they resulted in partial epimerization, generating D ,L ‐ or meso‐lactide polymers with enhanced biodegradability. A blend of PLLA‐r‐PCL [82/18; PLLA = poly(L ‐LA) and PCL = poly(ε‐caprolactone)] and PDLA‐r‐PCL [79/21; PDLA = poly(D ‐LA)] prepared by the solution‐casting method generated a stereocomplex, the melting temperature of which was about 40 °C higher than that of the nonblended copolymers. A blend of PLLA‐b‐PCL (85/15) and PDLA‐b‐PCL (82/18) showed a lower elongation at break and a remarkably higher tensile modulus than stereocomplexes of PLLA‐r‐PCL/PDLA‐r‐PCL and PLLA/PDLA. The biodegradability of a blend of PLLA‐r‐PCL (65/35) and PDLA‐r‐PCL (66/34) with proteinase K was higher than that of PLLA‐b‐PCL (47/53) and PDLA‐b‐PCL (45/55), the degradability of which was higher than that of a PLLA/PDLA blend. A blend film of PLLA‐r‐PDLLA (69/31)/PDLA‐r‐PDLLA (68/32) exhibited higher degradability than a film of PLLA/PDLLA [PDLLA = poly(D ,L ‐LA)]. A stereocomplex of PLLA‐r‐PCL‐r‐PDMO [80/18/2; PDMO = poly(L ‐3,D ,L ‐6‐dimethyl‐2,5‐morpholinedion)] with PDLA‐r‐PCL‐r‐PDMO (81/17/2) showed higher degradability than PLLA‐r‐PDMO (98/2)/PDLA‐r‐PDMO (98/2) and PLLA‐r‐PCL (82/18)/PDLA‐r‐PCL (79/21) blends. The tensile modulus of a blend of PLLA‐r‐PCL‐r‐PDMO and PDLA‐r‐PCL‐r‐PDMO was much higher than that of a blend of PLLA‐r‐PDMO and PDLA‐r‐PDMO. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 438–454, 2005     

Sorption of a fluorescent whitening agent (Tinopal CBS) onto modified cellulose fibers in the presence of surfactants and salt

The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostatic interaction among the charged headgroup of the surfactant and the charged fiber surface.     

Surface Hydrophilicities and Enzymatic Hydrolyzability of Biodegradable Polyesters, 2

Control of the surface hydrophilicities and enzymatic hydrolyzability of hydrophobic aliphatic polyesters such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) [i.e. poly(L ‐lactic acid) (PLLA)] was attempted by coating with hydrophilic poly(vinyl alcohol) (PVA). The PVA coating was carried out by immersion of the PCL and PLLA films in PVA solutions. The effects of PVA coating on the hydrophilicities were monitored by dynamic contact angle measurements, while the enzymatic hydrolyzability of the PVA‐coated PCL and PLLA films was evaluated by the weight losses after Rhizopus arrhizus lipase‐ and proteinase K‐catalyzed hydrolysis, respectively. It was found that the PVA coating successfully enhanced the hydrophilicities of the aliphatic polyester films and significantly suppressed enzymatic hydrolyzability of the aliphatic polyester films, excluding the PCL film coated at a very low concentration such as 0.01 g · dL^?1 and the crystallized PLLA film coated at 1 g · dL^?1, for which slight enhancement and no significant enhancement, respectively, were observed in the enzymatic hydrolyzability. Moreover, the hydrophilicities and enzymatic hydrolyzability of the aliphatic polyester films were controllable to some extent by varying the PVA solution concentration and the film crystallinity.

Advancing contact angle (θ_a) of PCL, PLLA‐C, and PLLA‐A films before and after the PVA coating by immersion in 1 g · dL^?1 solution.     

Effect of polyelectrolytes and polyelectrolyte mixtures on the electrokinetic potential of dispersed particles. 1. Electrokinetic potential of polystyrene particles in solutions of surfactants, polyelectrolytes and their mixtures

The effect of cationic and anionic surfactants, as well as cationic and anionic polyelectrolytes (PE), their binary mixtures on the electrokinetic potential of monodisperse carboxylated polystyrene (PS) particles as a function of the reagents dose, pH, the charge density (CD) of polymers, the surfactant/PE and binary PE mixture composition, and sequence of components addition to the suspension has been studied. It has been shown that addition of increasing amount of anionic surfactant/polyelectrolytes increases the absolute value of the negative zeta-potential of PS particles; this increase is stronger the CD of the PE and pH of the system are higher. Adsorption of cationic surfactant/polyelectrolytes leads to a significant decrease in the negative ζ-potential and to overcharging the particles; changes in the ζ-potential are more pronounced for PE samples with higher CD and for suspensions with lower pH values. In mixtures of cationic and anionic PE, in a wide range of mixture composition, the ζ-potential of particles is determined by the adsorbed amount of the anionic polymer independently of the CD of PEs and the sequence of addition of the mixture components. The isoelectric point of the surface is reached at the adsorbed amount of positive charges of PE that is approximately equal to the surface CD of particles. The laws observed were explained by features of macromolecules conformation in adsorbed mixed PE layers. Considerations about the role of coulombic and non-coulombic forces in the mechanism of anionic/cationic PE adsorption are presented.     

Hydrolytic And Enzymatic Degradation Characteristics Of Biodegradable Aliphatic Polysters

Aliphatic polyesters, especially those derived from lactide (PLA), glycolide (PGA) and ε-caprolactone (PCL), are being investigated worldwide for applications in the field of surgery (suture material, devices for internal bone fracture fixation), pharmacology (sustained drug delivery systems), and tissue engineering (scaffold for tissue regeneration) [1,2]. This is mainly due to their good biocompatibility and variable degradability. These polymers present also a growing interest for environmental applications in agriculture (mulch films) and in our everyday life (packaging material)as the development of biodegradable materials is now considered as one of the potential solutions to the problem of plastic waste management.For both biomedical and environmental applications, it is of major importance to understand the degradation characteristics of the polymers. The hydrolytic degradation of aliphatic polyesters has been investigated by many research groups. Our group has shown that degradation of PLAGA large size devices is faster inside than at the surface. This heterogeneous degradation is due to the autocatalytic effect of carboxylic endgroups formed by ester bond cleavage. Moreover,degradation-induced morphological and compositional changes were also elucidated. In the case of PCL, the hydrolytic degradation is very slow due to its hydrophobicity and crystallinity.The enzymatic degradation of these polymers has been investigated by a number of authors. A specific enzyme, proteinase K, has been shown to have significant effects on PLA degradation. This enzyme preferentially degrade L-lactate units as opposed to D-lactate ones, amorphous zones as opposed to crystalline ones [3]. The enzymatic degradation of PCL polymers has also been investigated. A number of lipase-type enzymes were found to significantly accelerate the degradation of PCL despite its high crystallinity. In the case of PLA/PCL blends, the two components exhibited well separated crystalline domains. The selective degradation of PCL or PLA components by enzymes revealed the inner morphology of the blends with formation of microsphere-like or island-like structures [5].     

Synthesis and Characterization of Biodegradable Poly(ϵ-caprolactone)-b-Poly(L-lactide) and Study on Their Electrospun Scaffolds

A series of multi-block copolymers, poly(L-lactide)-b-poly (?-caprolactone) (PLLA-b-PCL) were synthesized. The first step of the synthesis consisted of the transesterification between the PLLA and 1,4-Butanediol, followed by the copolymerization of PLLA-diols and PCL, using isophorone diisocyanate (IPDI) as a coupling agent. The synthesized polymers were characterized by Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). PLLA/PCL block copolymers were electrospun into ultrafine fibers. The morphology of the electrospun fibrous scaffolds were investigated by Scanning Electron Microscopy (SEM). Results showed that the morphology and diameter of the fibers were affected by the electrospinning solution concentrationan and different weight ratio of PLLA/PCL. These electrospun PLLA-b-PCL fibrous membranes exhibited good flexibility and deformability. In comparison with the electrospun PLLA membrane, the electrospun fibrous membranes of PLLA-b-PCL demonstrated an enhanced elongation with still high tensile strength and Young's modulus to be beneficial for tissue engineering scaffolds.     

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.     

Relationship between enzyme adsorption and enzyme-catalyzed degradation of polylactides

The adsorption of proteinase K on PLLA and PDLA films was studied by CA, surface tension, and microscopic measurements. ESEM clearly shows that proteinase K can irreversibly adsorb on PLLA film. In contrast, no enzyme adsorption was detected on PDLA film under the same conditions. The CA of PLLA film rapidly decreases after immersion in Tris buffer containing proteinase K, whereas that of PDLA remains unchanged. These findings indicate that enzyme adsorption may be a prerequisite for enzymatic degradation of polylactide substrates. Surface tension measurements allow calculation of the average area occupied per proteinase K molecule. The results show that the enzyme molecules exhibit a more compact conformation at higher temperature.     

Morphological changes of annealed poly‐ε‐caprolactone by enzymatic degradation with lipase

The effects of crystallinity and temperature on enzymatic degradation of poly‐ε‐caprolactone (PCL) films and structural changes after degradation have been studied using weight loss, differential scanning calorimetry, and optical microscopy. The weight loss during the enzymatic degradation of PCL suggested that the extent of biodegradation and the rate of degradation strongly depend on the initial crystallinity. PCL films of lower crystallinity (24%) degraded much faster than films of higher crystallinity (45%). The crystallinity of low‐crystalline PCL films increased with increasing degradation time, whereas the crystallinity of high‐crystalline PCL films decreased with time. The spherulite size increased with increasing degradation time for low‐crystalline samples but decreased with time for high‐crystalline samples. These results revealed that degradation occurs first in the amorphous region where the degradation rate is much higher, and the crystalline region of the PCL film started to degrade simultaneously for those PCL with higher crystallinity. The enzymatic degradation of PCL proceeded from the free amorphous to restricted amorphous followed by lamellar edges, where PCL chains have higher mobility irrespective of hydrolysis temperature. Caproic acid was identified as the primary product formed after degradation and confirmed by proton nuclear magnetic resonance spectroscopy, suggesting that degradation occurs through the depolymerization mechanism. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 202–211, 2010     

A new strategy for sustainable polymer recycling using an enzyme: poly(ε‐caprolactone)

Enzymatic degradation and polymerization using an enzyme were analyzed with respect to the establishment of a sustainable chemical recycling system for poly(ε‐caprolactone) (PCL) which is a typical biodegradable synthetic plastic. As the typical example, the enzymatic degradation of PCL having an M_n of 110 000 using lipase CA in toluene containing water at 70°C for 6 h afforded a unimodal oligomer having an M_n of about 1 000 quantitatively consisting of linear and cyclic oligomers. This was again polymerized by lipase CA in toluene under restricted water concentration to produce PCL having an M_n of greater than 70 000.     

Effect of sodium dodecyl sulfate and cetyltrimethylammonium bromide catanionic surfactant on the enzymatic hydrolysis of Avicel and corn stover

Nonionic surfactants could effectively improve the enzymatic hydrolysis efficiency of lignocellulose, while small molecule anionic and cationic surfactants usually inhibited the enzymatic hydrolysis. The results showed that the anionic surfactant sodium dodecyl sulfate (SDS) could improve the enzymatic hydrolysis efficiency of Avicel at the concentration range of 0.1–1 mM, but it did inhibit enzymatic hydrolysis at higher concentration. Cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to regulate the surface charge of SDS; thereby catanionic surfactant SDS-CTAB was formed. The effect of SDS-CTAB catanionic surfactant with varied molar ratios on the enzymatic hydrolysis of pure cellulose and corn stover at various enzymatic hydrolysis environments was investigated. SDS-CTAB could increase the enzymatic hydrolysis of corn stover at high solid loading from 33.3 to 42.4%. Using SDS-CTAB could reduce about 58% of the cellulase dosage to achieve 80% of the enzymatic hydrolysis of corn stover. SDS-CTAB catanionic surfactant could regulate the surface charge of cellulase in the hydrolyzate and reduce the non-productive adsorption of cellulase on the lignin, thereby improving the enzymatic hydrolysis efficiency of lignocellulose.