Compatibilization of immiscible poly(lactic acid)/poly(ε-caprolactone) blend through electron-beam irradiation with the addition of a compatibilizing agent

The aim of this study was to compatibilize immiscible poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend by using electron-beam radiation method with the addition of a compatibilizing agent. Glycidyl methacrylate (GMA) was chosen as the compatibilizing agent, in the expectation that the GMA plays a role as a monomeric compatibilizer and a reactive agent at the interface between the PLA and the PCL phases. Compatibilization process has been investigated through the melt mixing of the PLA/PCL and the GMA by using a twin-screw extruder and the exposure of the PLA/PCL/GMA mixture to electron-beam radiation at room temperature. The melt mixing process was performed to locate the GMA at the interface, thereby expecting a finer morphology due to the GMA as the monomeric plasticizer. The exposure process was carried out to induce definite interfacial adhesion at the interface through electron-beam initiated cross-copolymerization by the medium of the GMA as the reactive agent. To investigate the results of this compatibilization strategy, the morphological, mechanical, and rheological properties of the blend were analyzed. The morphological study clearly showed the reduced particle size of dispersed PCL domains and significantly improved interfacial adhesion by the electron-beam irradiation with the addition of the GMA. The stress–strain curves of the blends irradiated at less than 20 kGy showed the typical characteristics of ductile materials. The tensile properties of the blend were strongly affected by the dose of irradiation.     

Morphology and thermal degradation studies of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) biodegradable polymer blend nanocomposites with TiO2 as filler

The morphology and thermal stability of melt-mixed poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend nanocomposites with small amounts of TiO₂ nanoparticles were investigated. The nanoparticles were mostly located in the PLA phase, with good dispersion of individual particles, although significant aggregation was also visible. The thermal stability and degradation behaviour of the different samples were studied using thermogravimetric analysis (TGA) and TGA-Fourier-transform infrared (FTIR) spectroscopy. Neat PCL showed better thermal stability than PLA, but the degradation kinetics revealed that PLA had a higher activation energy of degradation than PCL, indicating its degradation rate more strongly depends on temperature, probably because of a more complex degradation mechanism based on chain scission and re-formation. Blending of PLA and PCL reduced the thermal stabilities of both polymers, but the presence of TiO₂ nanoparticles improved their thermal stability. The nanoparticles also influenced the volatilization of the degradation products from the blend, acted as degradation catalyst and/or retarded the escape of volatile degradation products.     

Synthesis and characterization of biodegradable pH-sensitive hydrogels based on poly(?-caprolactone), methacrylic acid, and poly(ethylene glycol)

In this work, a novel biodegradable pH-sensitive hydrogel based on poly(?-caprolactone) (PCL), methoxpoly(ethylene glycol) (MPEG) and methacrylic acid (MAA) was prepared by UV-initiated free radical polymerization. The resulting macromonomers and hydrogels were characterized by FTIR and/or ¹H NMR. Swelling behaviour and pH sensitivity of the hydrogels were studied in detail. With increase in pH of aqueous medium from 1.2 to 7.2, swelling ratio of the hydrogels increased accordingly. The hydrolytic degradation behaviour was also investigated. The prepared biodegradable pH-sensitive hydrogel based on PCL, MPEG, and MAA might have great potential application in smart drug delivery system.     

Effects of hyperbranched and linear architecture on properties of polymers composed of poly(ɛ-caprolactone) and hydroxycinnamic acid

Photoreactive and degradable polymers with linear and hyperbranched architectures which composed of poly(?-caprolactone) and hydroxycinnamic acid or its substituted derivatives were synthesized by thermal melt-polycondensation. The chemical structures of the polymers were confirmed by FTIR and ¹H NMR measurements. The polymers showed good photoreactivities and fluorescent properties, and the hyperbranched polymers showed higher photoreactive speed and weaker fluorescence properties. These polymers had excellent thermal stabilities due to the rigid conjugated structures and the π-π strcking interaction of the cinnamoyl group, especially for the hyperbranched polymer. Moreover, the hydrolysis experiments and the XRD results revealed that the hyperbranched and linear polymers are amorphous and crystalline, respectively, and the degradation rate of amorphous polymers are faster than crystalline samples.     

Preparation and characterization O-lauroyl chitosan/poly (L-lactic acid) blend membranes by solution-casting approach

O-Lauroyl chitosan/poly(L-lactide) (OCS/PLLA) blend membranes with different compositions were prepared by solution-casting approach using chloroform as common solvent. The experimental results of FT-IR, DSC and WAXD indicated that inter-association hydrogen-bond interactions existed between OCS and PLLA in the blend membranes. And SEM observation confirmed that the blend membranes with suitable compositions were compatible.     

Binary blends based on poly(vinyl chloride) and multi-block copolymers containing poly(ϵ-caprolactone) and poly(ethylene glycol) segments

Binary blends based on poly(vinyl chloride) (PVC) were prepared both by casting from tetrahydrofuran (THF) and by mixing in the melt form, in a discontinuous mixer, PVC and multi-block copolymers containing poly(ϵ-caprolactone) (PCDT) and poly(ethylene glycol) (PEG) segments. PCDT-PEG copolymers were synthesized using a polycondensation reaction where the α,ω-bis-chloroformate of an oligomeric poly(ϵ-caprolactone) diol terminated (PCDT) and oligomeric PEG were employed as macromonomers. For comparison purposes, blends PVC with starting oligomers as well as with mixtures containing a typical low molecular plasticizer, dioctylphthalate (DOP), were also prepared. The copolymer miscibility was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The blend morphology was investigated by polarized light microscopy (PLM). A higher miscibility with PVC was observed for copolymers compared to PEG.     

Abiotic degradation of poly(dl-lactide), poly(ɛ-caprolactone) and their blends

An effective hydrolytic degradation of PDLLA, PCL and their blends in a phosphate-buffered solution of pH 4.0 at 37 °C for 18 weeks was achieved, observing a considerably faster degradation of PDLLA as compared to PCL due to the hydrophobic and semicrystalline nature of PCL matrix, able to partially prevent water diffusion into the bulk specimen.DSC and FTIR results indicated that PCL phase, in compositions rich in PCL, was very stable against hydrolysis, but the presence of PDLLA in the PDLLA/PCL blends seemed to catalyze the hydrolytic degradation of the PCL phase, probably associated to easier diffusion of water into the PCL domains by the presence of PDLLA amorphous regions. This last trend was proportional to the content of PDLLA in the blends, excepting for the composition 64%PDLLA/36%PCL. It was confirmed that PCL molecules partially delayed hydrolysis of PDLLA molecules, according to FTIR analysis, and the water diffusion prevention level was proportional to the content of PCL in the blends, except for the system 64%PDLLA/36%PCL, which presented a lower extent of degradation than neat PDLLA but higher than the blend 80%PDLLA/20%PCL. This indicated that PCL molecules did not significantly impede hydrolysis of PDLLA molecules in this blend, possibly due to the achievement of a particular structure of the PDLLA/PCL interphase in this blend. In general, hydrolysis of PDLLA/PCL blends was found to be a complex phenomenon depending not only on the content of both polymer phases, but also on the polymer phase crystallinity and morphology.     

Preparation and characterization of thermosensitive pluronic F127-b-poly(ɛ-caprolactone) mixed micelles

The mixed micelles composed of pluronic F127-b-poly(?-caprolactone) (F127-CL) and bovine serum albumin (BSA) or polylactic acid (PLA) were fabricated for application as promising drug carriers. F127-CL copolymers were characterized by (1)H NMR, FT-IR, GPC, DSC, XRD and POM. They can self-assemble into micelles in water by solvent evaporation method. The thermo-responsivities of the pure and mixed micelles were investigated. The drug release behaviors were investigated in phosphate-buffered solution (PBS) and acetate buffer solution (ABS), respectively, at 37°C. The hemolysis and coagulation assay and the tumor cell growth inhibition assays were further evaluated. The morphologies of pure micelles underwent from the coexistence of the rods and spheres to the spheres with increasing the lengths of CL. The micelle behaviors were influenced with the addition of BSA and PLA. Both pure and mixed micelles of F127-CL with CL length of 200 show thermo-responsivities from 25 to 45°C, while form larger aggregations at high temperature. The hemolysis and coagulation assays showed that the micelles possess good blood compatibility. The cytotoxicity results showed that the copolymer was a safe carrier and the encapsulated doxorubicind.HCl remained its potent anti-tumor effect. The in vitro release profiles displayed a sustained release of DOX.HCl from the micelles. The block copolymers can be great potential as a nanocontainer in drug delivery systems.     

Thermal degradation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) or poly(ethylene glycol)

Thermodegradative investigations of two classes of multi-block copolymers containing poly(D,L-lactic-glycolic acid) (PLGA) and either poly(ethylene glycol) (PEG) or poly(ϵ-caprolactone) diol-terminated (PCDT) segments were performed. In particular, the influence of the type and length of the segments as well as of the molar ratio between the D,L-lactic acid (LA) and glycolic acid (GA) residues was investigated at 180°C in air by viscometry, FT-IR analysis and isothermal thermogravimetry. The thermal oxidative degradation of these materials is largely affected by the LA/GA ratio, a higher LA content generally imparting higher stability. The FT-IR analysis suggests that, depending on the composition of the PLGA segments, degradative processes are triggered which can lead to a preferential degradation of the blocks.     

Enhanced photodegradation of TiO2-containing poly(ε-caprolactone)/poly(lactic acid) blends

The calamitous accumulation of plastic waste in the environment, especially single-use disposables, calls for new approaches to materials design. One method to address the persistence of plastics beyond their intended use is to impart them with functionalities that will either allow for their recyclability or their degradation to basic natural components. This work focuses on the fabrication of photodegradable polyester blends and investigates the impact of compatibilization on photodegradation rates. Specifically, we blended poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) polymers by (reactive) extrusion in the presence or absence of dicumyl peroxide (DCP), a radical generator, and titanium dioxide (TiO₂), an inorganic photocatalyst. We examined the effects of DCP and TiO₂ loadings as well as copolymer composition on the thermomechanical properties, photodegradability, and morphology. We found that the inclusion of TiO₂ dramatically increased flexural moduli and photodegradation rates in both dry and wet conditions, while reactive compatibilization had little effect of the tested properties. This simple and scalable approach is promising to fabricate materials that can readily photodegrade.     

Effect of halloysite nanotubes on the thermal degradation behaviour of poly(ε-caprolactone)/poly(lactic acid) microfibrillar composites

This paper reports on the thermal degradation behaviour and kinetics of halloysite nanotubes containing microfibrillated poly(ε-caprolactone) (PCL)/poly(lactic acid) (PLA) blends. It was found that the nanotubes probably catalyzed the PLA degradation, and that the free radicals formed during the PLA degradation initiated PCL degradation at lower temperatures, maybe in combination with halloysite nanotubes (HNT) catalysis. Drawing to form microfibrillated nanocomposites had little influence on the degradation behaviour of these materials, but pre-mixing of the HNT with PLA or PCL prior to melt-mixing and extrusion-drawing of the blends did influence the degradation behaviour, but in different ways. No evidence could be found that the presence and amount of HNT, or the mode of preparation, had an influence on the degradation mechanism, as evidenced through a Fourier-transform infrared (FTIR) analysis of the degradation products.     

Controlled-release and antibacterial studies of doxycycline-loaded poly(ε-caprolactone) microspheres

The objective of the present study is to achieve doxycycline’s maximum therapeutic efficacy. Doxycycline-loaded poly(ε-caprolactone) microspheres were prepared by water-in-oil-in-water (w/o/w) double emulsion solvent evaporation technique with different formulation variables such as concentrations of drug and polymer. The effects of these variables on surface morphology, particle size distribution, encapsulation efficiency, and in vitro release behavior were examined. To observe the nature of microspheres, X-ray diffraction studies were carried out. The release data obtained were determined using various kinetic models and Korsmeyer–Peppas model showed an acceptable regression value for all compositions. Antibacterial efficiency of doxycycline-loaded poly(ε-caprolactone) microspheres were assessed by determining Minimum Inhibition Concentration (MIC) by standard tube dilution method against four standard pathogenic strains. The in vitro drug release studies were carried out in phosphate buffer solution (pH 7.2). The results showed marked retardation of doxycycline release and higher percentage of polymer gave longer drug release profile. This may definitely provide a useful controlled-release drug therapy and also prove to be effective over a long period of time (76 h).     

Chemical–physical behavior of hydrogels of poly(vinyl alcohol) and poly(ethylene glycol)

New hydrogels based on polyethylene glycol (PEG) and poly(vinyl alcohol) (PVA) of different degrees of hydrolysis were synthesized. To form the network the PEG was modified at their ends with acyl chloride groups to be used as the crosslinking agent. The compositions of the hydrogels were between 50% and 90% by weight of PEG and PVA of various degrees of hydrolysis were used. It was found that the degree of hydrolysis of the PVA and the PEG content influence the equilibrium water content of the hydrogel. The process of swelling of all the hydrogels prepared followed a second-order kinetics.     

Preparation and properties of poly(vinyl alcohol)/exfoliated α-zirconium phosphate nanocomposite films

In this work, poly(vinylalcohol)(PVA)/exfoliated α-zirconium phosphate(e-α-ZrP) nanocomposites of various compositions were created by a solution casting method. The α-ZrP compound was synthesized by refluxing. The characteristic properties of the PVA/e-α-ZrP composite films were examined by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and tensile tests. Tensile tests indicated that with the loading of e-α-ZrP, the tensile strength and the elongation at break were increased by 17.3% and 26.6% compared to neat PVA, respectively. It is noteworthy that optimum film properties were obtained with 0.8 wt% e-α-ZrP, and higher proportions of e-α-ZrP, may be related to the aggregation of e-α-ZrP particles and deterioration of the film properties. On the whole, the nanocomposite PVA/e-α-ZrP systems had mechanical and thermal properties which were superior to that of the neat polymer and its conventionally filled composites.     

Purification, cloning and expression of an Aspergillus niger lipase for degradation of poly(lactic acid) and poly(ε-caprolactone)

A lipase from Aspergillus niger MTCC 2594 was purified 53.8-fold to homogeneity by hydrophobic interaction chromatography using octyl sepharose and the enzyme showed two protein bands with apparent molecular mass of 35 and 37 kDa respectively. The lipase exhibited maximum activity at pH 7.0 and 37 °C and was stable between pH 4.0 and 10.0 and temperatures up to 50 °C. The values of K_m and V_max were 3.83 mM and 32.21 μmol/min/mg respectively, using olive oil as substrate. Lipase encoding gene, lipA, coded for 297 amino acid residues with conserved pentapeptide sequence, G-H-S-L-G, was cloned and expressed in Pichia pastoris. Although lipA showed high homology with the known Aspergillus lipases, it exhibited differences in putative lid domain. Both native and recombinant lipases have potential for degradation of poly(lactic acid) and poly(ε-caprolactone), and the present study will serve as a baseline of initial studies for its exploitation in polymer degradation.     

Hydrophilic films based on poly(acrylic acid)–poly(vinyl methyl ether) blends cross-linked by gamma-radiation

Hydrophilic polymeric films based on blends of poly(acrylic acid) and poly(vinyl methyl ether) (PVME) were prepared by casting technique and were cross-linked by gamma-radiation. The films are soft and elastic in a dry state and form hydrogels upon immersion in water. Effect of absorbed dose on the gel fraction as well as on the swelling of the films in aqueous solutions of different pH is studied. It was found that addition of lower molecular weight PVME decreases the gelation dose, which is likely related to a decrease in glass transition temperature of the blends. In acidic media the films have low swelling degree because of suppression of carboxylic groups ionisation and formation of additional physical cross-links via interpolymer hydrogen bonding.     

Phase separation and phase dissolution in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

A blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile having the critical composition (80/20 PCL/SAN) was studied. This PCL/SAN blend having a lower critical solution temperature (LCST) phase boundary at 122 °C offered an excellent opportunity to investigate, firstly the kinetics of phase separation above LCST (125-180 °C), and secondly the kinetics of phase dissolution below LCST (50-115 °C). The blend underwent a temperature-jump above LCST where spinodal decomposition (SD) proceeded, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below LCST when the phase dissolution proceeded. Optical microscopy was used to observe the spinodal decomposition qualitatively while light scattering was used to characterize the phase separation and phase dissolution quantitatively. It was found that during phase dissolution the peak maximum moved towards a smaller angle (wavelength of concentration fluctuations increased) while the peak intensity decreased. This behavior was explained by a model. Also it was found that the fastest phase dissolution kinetics at 80 °C, which was characterized by an apparent diffusion coefficient, was about 10 times slower than the kinetics of phase separation at 180 °C.     

Ageing of plasticized poly(lactic acid)/poly(β-hydroxybutyrate) blend films under artificial UV irradiation and under real agricultural conditions during their application as mulches

The paper is aimed on the investigation of natural ageing of plasticized poly(lactic acid)/poly(β-hydroxybutyrate) PLA/PHB blend films during their one-season application as mulches under real field conditions in the western part of Slovakia. Acetyl tributyl citrate (ATBC) was used as the plasticizer. The analysis was performed on three differently exposed parts of the foil: i) buried in soil, ii) exposed to sunlight, and iii) shadowed by plants. In parallel, UV irradiation of the blend under laboratory controlled conditions (constant temperature of 30°C and relative humidity of 55 %) was carried out. The degradation effect was followed by changes in the molar mass, chemical and crystalline structures, as well as in thermal and mechanical properties. The ternary PLA/PHB/ATBC blend lost its tensile properties faster when buried in soil than when exposed to sunlight. This result is in agreement with the data obtained for the UV-irradiated materials. Young’s modulus values showed a significant mechanical degradation under the UV irradiation as well as during natural ageing. The study was also focused on the influence of mulches on the yield and quality of sweet pepper production, characterized by carotenoids and vitamin C content.