Shape‐memory effects of radiation crosslinked poly(ϵ‐caprolactone)

Poly(?‐caprolactone) (PCL) with different molecular weight were crosslinked by γ‐radiation. The radiation crosslinking features were analyzed by Soxhlet extraction with toluene and the Charlesby–Pinner equation. The crosslinking degree is relative to molecular weight and radiation dose; the relation between sol fraction and dose follows the Charlesby–Pinner equation. All the samples were crystalline at room temperature, and the radiation crosslinking had a little effect on the crystallinity and the melting behavior of PCL. The shape‐memory results indicated that only those specimens that had a sufficiently high crosslinking degree (gel content is higher than about 10%) were able to show the typical shape‐memory effect, a large recoverable strain, and a high final recovery rate. The response temperature of the recovery effect (about 55°C) was related to the melting point of the samples. The PCL shape‐memory polymer was characterized by its low recovery temperature and large recovery deformation that resulted from the aliphatic polyester chain of PCL. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1589–1595, 2003     

Crystallization of poly(ε-caprolactone)

The isothermal crystallization behaviour of poly(ε-caprolactone), PCL, has been investigated by dilatometry and optical microscopy. Nucleation rates and spherulitic growth rates have been measured. At all temperatures tested a change in nucleation rate was observed early during the crystallization. Growth rates were linear over the whole of the crystallization range. The experimental results were analysed using the Avrami equation in which the experimentally observed time dependence of nucleation is used. The equation contains integer values of the Avrami exponent and describes adequately the crystallization behaviour of PCL. The difference between the apparent and true nucleation rates is emphasized, and difficulties in the calculation of rate constants are discussed.     

Blends of aliphatic polyesters. III. Biodegradation of solution-cast blends from poly(L-lactide) and poly(ε-caprolactone)

Phase-separated blend films were prepared with the solution casting method from poly(L -lactide) (PLLA) and poly(ε-caprolactone) (PCL) with different PLLA contents [X_PLLA (w/w) = PLLA/(PCL + PLLA)] and their biodegradation was investigated in soil up to 20 months by gravimetry, gel permeation chromatography, tensile testing, differential scanning calorimetry, and scanning electron microscopy. The nonblended PCL film and the blend film with X_PLLA = 0.25 disappeared in 4 and 12 months, respectively, while most of the initial mass remained for the blend film of X_PLLA = 0.75 and the nonblended PLLA film. The decrease in weight remaining, molecular weight, tensile strength, and elongation-at-break was higher for blend films of low X_PLLA. The melting temperature of PLLA in blend films of X_PLLA = 0.5 and 0.75, and of nonblended film, remained around 179°C upon biodegradation in soil for 20 months. The preferred biodegradation of PCL in blend films resulted in formation of microspheres of a PLLA-rich phase at the surface for the blend film of X_PLLA = 0.25 and the porous structure for blend films of X_PLLA = 0.5 and 0.75. Comparison of the weight loss of blend films in biodegradation in soil with that of the nonenzymatic hydrolysis in phosphate-buffered solution revealed preferred enzymatic degradation of PCL and insignificant attack to PLLA in the blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2259–2268, 1998     

Thermal and mechanical properties of poly(ε‐caprolactone) crosslinked with γ radiation in the presence of triallyl isocyanurate

Poly(?‐caprolactone) was crosslinked by γ radiation in the presence of triallyl isocyanurate. The influence of γ‐radiation crosslinking on the thermal and mechanical properties of poly(?‐caprolactone)/triallyl isocyanurate was investigated. Differential scanning calorimetry analyses showed differences between the first and second scans. Dynamic mechanical analysis showed an increase in the glass‐transition temperature as a result of the radiation crosslinking of poly(?‐caprolactone). Thermogravimetric analysis showed that γ‐radiation crosslinking slightly improved the thermal stability of poly(?‐caprolactone). The γ radiation also strongly influenced the mechanical properties. At room temperature, crosslinking by radiation did not have a significant influence on the Young's modulus and yield stress of poly(?‐caprolactone). However, the tensile strength at break and the elongation at break generally decreased with an increase in the crosslinking level. When the temperature was increased above the melting point, the tensile strength at break, elongation at break, and Young's modulus of poly(?‐caprolactone) were also reduced with an increase in the crosslinking level. The yield stress disappeared as a result of the disappearance of the crystallites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2676–2681, 2007     

Crystallization behavior of partially crosslinked poly(β‐hydroxyalkonates)/poly(butylene succinate) blends

Partially crosslinked poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate)/poly(butylene succinate) (PHBV/PBS) and poly(β‐hydroxybutyrate)/poly(butylene succinate) (PHB/PBS) blends were prepared by melt compounding with dicumyl peroxide. The effect of partial crosslinking on crystallization of the PHBV/PBS and PHB/PBS blends was investigated systematically. Differential scanning calorimetry results showed that the overall crystallization rates of both PHBV and PBS in their blends were enhanced considerably by the partial crosslinking. Similar results were also detected in the PHB/PBS blends. The polarized optical microscope observation displayed that the nuclei density of PHBV was increased while the spherulitic morphology did not change much. Conversely, the PBS spherulites turned into cloud‐like morphology after the partial crosslinking which is a result of the decrease in spherulite size, the reduction in interspherulite distance and the interconnection of fine PBS domains. Wide angle X‐ray diffraction patterns confirmed the enhancement in crystallization of the PHBV/PBS blends after the partial crosslinking without modification on crystalline forms of the PHBV and PBS components. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41020.     

Mechanical behavior of poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends

The mechanical properties of compatible poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blends were studied for samples prepared from both the melt and solution. The mechanical response was observed to be primarily dependent upon the variation of the glass transition temperature with blend composition. For certain compositions, varying the sample preparation scheme resulted in specimens of different modulus. This behavior was associated with differences in the degree of crystallinity.     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

Compatibility of low-density polyethylene–poly(ε-caprolactone) blends

The compatibility of low-density polyethylene (LDPE)–poly(ε-caprolactone) (PCL) was examined using the microscopic, the dynamic mechanical, and the DSC techniques. Morphological examination revealed that at low PCL concentrations, when specimens are severaly quenched, a uniform microspherulitic structure is formed. The dynamic mechanical spectra, at isochronous conditions (110 Hz), indicate very limited mixing of the amorphous phase of the two components at the intermediate compositions. More drastic relaxation shifts were observed at the extremes of the composition range. Ultimate strength and elongation at break are characteristic of a mechanically compatible system at high and low PCL contents. In the intermediate composition range their low value indicates phase separation. DSC measurements showed a nonlinear dependence of bulk crystallinity on blend composition; also, that the presence of PE enhances the degree of PCL crystallinity. Thermal history strongly affects bulk crystallinity. At elevated temperatures, near the mp of PE, thermal treatment affects considerably the melting point of the PE crystals.     

Compatibility of isotactic polypropylene/poly(ε-caprolactone) blends

Blends of poly(ε-caprolactone) (PCL)/isotactic polypropylene (iPP), in the solid state and at compositions spanning the complete range, were characterized using the dynamic mechanical, DSC, and optical microscopy techniques. Morphology examination revealed that increasing the PCL content causes a decrease of spherulitic size. The loss modulus spectra at isochronous conditions (110 Hz) reveal an heterophase system with limited phase mixing between the amorphous components of the blend constituents. Melt-mixing and quenching using the DSC causes a considerable melting point depression of the PCL component, attributed to its miscibility with the polypropylene amorphous phase. Addition of PCL caused an increase of iPP crystallinity at intermediate compositions, while at low PCL levels the presence of iPP crystals hinders the growth of PCL crystallites.     

Gelatin microspheres crosslinked with γ‐ray: Preparation,sorption of proteins,and biodegradability

A new type of gelatin microspheres was manufactured with the crosslinking method by using γ‐ray irradiation. Microspheres thus obtained were characterized by microscopic observation and enzymatic degradability. The mean diameter of the microspheres was in the range from 2.4 to 3.6 μm and the size distribution was quite small. The size decreased with increasing the shear rate of the emulsifier used in the preparation and was not affected by the radiation dose. The enzymatic degradability decreased with increasing the radiation dose and decreasing the gelatin concentration of the microsphere. In other words, the rate of the enzymatic decomposition of microspheres can be controlled by these two parameters. These trends were consistent with our previous results for the gel sheet made of gelatin. Their sorption of proteins was also investigated with the use of three types of proteins labeled by fluorescent pigment. From the fluorescence micrographs, it was observed that the gelatin microspheres adsorbed only proteins having the opposite charge. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3083–3087, 2004     

Improvement of processability of poly(ε‐caprolactone) by radiation techniques

Improvement of processability of Poly(ε‐caprolactone) (PCL) was achieved by introduction of a branch structure using gamma‐irradiation from a ⁶⁰Co source. Irradiated PCL has higher molecular weight by producting a branch structure. Hence, the irradiation at a lower dose, such as 3 Mrad, leads to a higher melt viscosity. The branched structure gave improved properties for dynamic viscoelasticity and elongational viscosity. High elongational viscosity was observed by entanglement due to branch chain formed during irradiation, and the elongational viscosity for 3 Mrad is higher than 1.5 Mrad. Due to a higher elongational viscosity, PCL foam can be produced by a molding process. Foam produced from irradiated PCL pellets at 3 Mrad has honeycomb‐like structure, and the foam showed higher enzymatic degradation compared to film samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1815–1820, 1999     

Crystallization kinetics of poly-ε-caprolactone from poly-ε-caprolactone/poly(vinyl chloride) solutions

The polymer–polymer solution of poly(vinyl chloride) and poly-ε-caprolactone yields an excellent system for studying the crystallization kinetics of a crystallizable component from a polymer–polymer solution. Unlike previous studies of isotactic–atactic polystyrene solutions for which the glass transition temperature is invariant with composition, this system exhibits a marked dependence of T_g on the composition. The experimental data dE^?(modulus)/dt (psi^?/min) were obtained over a composition range of 40 to 70 wt-% poly-ε-caprolactone. With the appropriate modification of the spherulitic growth rate equation, the expression approximated a reasonable fit of the experimental data. This demonstrates a marked dependence of the crystallization rate on concentration. Secondary observations of this investigation show a slower crystallization rate for high molecular weight poly-ε-caprolactone and a slow secondary crystallization step. Both homopolymer poly-ε-caprolactone and poly-ε-caprolactone in the poly-ε-caprolactone/poly(vinyl chloride) solution show a slow (relative to the nucleation-controlled step) crystallization stage considered to involve a slow diffusion mechanism.     

Hydrolytic degradation of poly(oxyethylene)–poly-(ε-caprolactone) multiblock copolymers

The degradation of poly(oxyethylene)–poly(ε-caprolactone) (POE–PCL) multiblock copolymers was investigated at 37°C in a 0.13M, pH 7.4 phosphate buffer selected to mimic in vivo conditions. The copolymers were obtained by coupling polycaprolactone diols and poly(ethylene glycol) diacids using dicyclohexylcarbodiimide as coupling agent. Various techniques, such as weighing, size exclusion chromatography, infrared, ¹H nuclear magnetic resonance, differential scanning calorimetry, and X-ray diffractometry, were used to monitor changes in total mass, water absorption, molar mass, thermal properties, degree of crystallinity, and composition. The results showed that introduction of POE sequences considerably increased the hydrophilicity of the copolymers as compared with PCL homopolymers. Nevertheless, the degradability of PCL sequences was not enhanced due to the phase separation between the two components. Significant morphological changes were also observed during the degradation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 989–998, 1998     

Influence of thermal stabilizers on diffusion of poly(ϵ-caprolactone) in poly(vinyl chloride)/poly(ϵ-caprolactone) blends

The influence of thermal stabilizers on the poly(ϵ-caprolactone) (PCL) diffusion in poly(vinyl chloride) (PVC)/PCL blends was studied with the addition of various concentrations of dibasic lead phthalate and dibutyltin dilaurate. The rate of PCL diffusion was followed by differential scanning calorimetry and IR spectroscopy in three series of experiments: the migration of PCL at the surface of the sample; the extraction of PCL in a fluid surrounding the sample; and the sorption of liquid PCL in the blend. In the last two series, mass losses and mass uptakes were measured as a function of time. As compared to the blend without additive, dibutyltin dilaurate induces an increase of the PCL rate of diffusion whereas dibasic lead phthalate gives a decrease. These trends are explained by: first, the formation of an associative complex between dibutyltin dilaurate and PVC, which can compete with the PVC/PCL interactions in the blend and thus favor the PCL migration; and, second, the modification of the T_g of the blend induced by the addition of a third component, which can modify the diffusion rate by changing the free volume fraction at the diffusion temperature. T_g decreases slightly in the presence of dibutyltin dilaurate but increases with dibasic lead phthalate. © 1996 John Wiley & Sons, Inc.     

Coating of cotton yarn with poly(vinyl alcohol) and poly(N‐vinyl‐2‐pyrrolidone) crosslinked via ultraviolet radiation

The coating of cotton fiber is used in the textile industry to increase the mechanical resistance of the yarn and their resistance to vibration, friction, impact, and elongation, which are some of the forces to which the yarn is subjected during the weaving process. The main objective of this study was to investigate the use of synthetic hydrophilic polymers, poly(vinyl alcohol) (PVA), and poly(N‐vinyl‐2‐pyrrolidone) (PVP) to coat 100% cotton textile fiber, with the aim of giving the fiber temporary mechanical resistance. For the fixation of the polymer on the fiber, UV‐C radiation was used as the crosslinking process. The influence of the crosslinking process was determined through tensile testing of the coated fibers. The results indicated that UV‐C radiation increased the mechanical resistance of the yarn coated with PVP by up to 44% and the yarn coated with PVA by up to 67% compared with the pure cotton yarn, that is, without polymeric coating and crosslinking. This study is of great relevance, and it is important to consider that UV‐C radiation dispenses with the use of chemical substances and prevents the generation of toxic waste at the end of the process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of wide‐range γ‐irradiation doses on the structures and properties of 4,4′‐dicyclohexyl methane diisocyanate based poly(carbonate urethane)s

For medical applications, 4,4′‐dicyclohexyl methane diisocyanate (HMDI)‐based poly(carbonate urethane)s were synthesized from HMDI and 1,4‐butanediol as hard segments and poly(carbonate diol) (number‐average molecular weight = 2000 g/mol) as soft segments. The effects of wide‐range γ irradiation on the samples were examined through a series of analytical techniques. Scanning electron microscopy revealed that γ irradiation etched and roughened the surfaces of the irradiated samples. The gel content and crosslinking density measurements confirmed that crosslinking occurred along with degradation at all of the investigated irradiation doses and the degree of both crosslinking and degradation increased with increasing irradiation dose. Fourier transform infrared spectroscopy demonstrated that chain scission in the γ‐irradiated samples occurred at the carbonate and urethane bonds. The decreasing molecular weight and tensile strength indicated that the degradation increased with the γ‐irradiation dose. Differential scanning calorimetry and dynamic mechanical thermal analysis indicated that γ irradiation had no significant effect on the phase‐separation structures. There was a slight reduction in the contact angle. An evaluation of the cytotoxicity demonstrated the nontoxicity of the nonirradiated and irradiated polyurethanes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41049.     

Effect of processing additives on (bio)degradability of film-blown poly(ε-caprolactone)

Poly(ε-caprolactone)s (PCL) with slip masterbatch, Erucamide, SiO₂ and Erucamide + CaCO₃ as low-molecular-weight processing additives, were film-blown in a single screw extruder. The films and recycled PCL without additives were exposed to composting, anaerobic sewage sludge (37 and 55°C), pure fungal culture, and chemical hydrolysis at two pH (7 and 10.5) and at two temperatures (room temperature and 50°C). Recycling and addition of processing additives resulted in a slightly slower degradation rate compared with the degradation of pure PCL. The degradations in biotic environment were generally faster than in abiotic environment. Higher degradation rates are observed in more complex environments (composts and anerobic sewage sludge) due to synergism between high temperature and a richer fauna of microorganisms. In the biotic environments, faster reductions in number-average molecular weight (M _n) than in weight-average molecular weight (M _w) were observed. A decrease of M _n with up to 75–80% was estimated for composted pure PCL, while similar samples in anaerobic sludge at 55°C were completely degraded in 50 days. The mechanical properties of the samples subjected to composting exhibited a more rapid enbrittlement compared to the samples subjected to abiotic hydrolysis. The observed increase in crystallinity with increasing degree of degradation is explained by crystallization made possible by chain cleavage in the amorphous phase. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 61–74, 1998     

Biodegradation study on poly(ε‐caprolactone) with bimodal molecular weight distribution

Poly(ε‐caprolactone) (PCL) of bimodal molecular weight distribution was exposed to the action of enzymes‐lipases from Aspergillus oryzae in phosphate buffer at pH 7 and 37°C, and those produced in situ by Bacillus subtilis in nutrient medium at 30°C for 42 days. The occurrence of biodegradation is proved on the basis of the weight loss, decrease of molecular weight, carbonyl index, crystallinity, and development of cracks on the PCL surfaces. In the case of Bacillus subtilis, the degradation (10 wt % loss of PCL) proceeds faster in comparison with lipase from Aspergillus oryzae (2.6 wt % loss of PCL), where the degradation process seems to stop during 14 days of experiment. The gel permeation chromatography results reveal that preferential degradation of lower molecular portion did not occur but it is assumed that PCL chains were cleaved in accordance with particular degradation mechanism that depends significantly on biological agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Biodegradable supramolecular composites of poly(ε‐caprolactone) and low‐molecular‐weight organic gelators

When a homogeneous hot liquid of poly(ε‐caprolactone) (PCL) with (R)‐12‐hydroxystearic acid (HSA) or N‐carbobenzyloxy‐L ‐isoleucylaminooctadecane (CIA) was gradually cooled to room temperature, the mixture became gelatinous material and then solidified to give a PCL/HSA or PCL/CIA composite. The rheological measurements of the mixtures of PCL with HSA and CIA revealed that the organogels are formed at around 70–50°C and 100–73°C during the cooling process, respectively. Furthermore, the formation of supramolecular fibrillar networks was confirmed by the microscopic and differential scanning calorimetric analyses. The tensile moduli of both the composites were improved by the addition of CIA and HSA. Both the composites showed so high biodegradability as PCL. The fibrillar networks of the composites were also regenerated during the repeated cooling process from the isotropic liquid. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Intramolecular effects in cellulose mixed benzyl ethers blended with poly(ε-caprolactone)

Tri-O-benzyl cellulose, tri-O-p-fluorobenzyl cellulose, and a corresponding series of cellulose mixed benzyl ethers were synthesized and blended with poly(ε-caprolactone) (PCL). Mechanical and thermal analyses indicated that none of the cellulose benzyl ethers of the cellulose mixed benzyl ethers was miscible with PCL. However, there was evidence of a limited degree of compatibility that exhibited a dependence on the substituent ratio, or copolymer composition, of the cellulose mixed benzyl ethers. The weak interactions in these blends were found to be nonspecific, and thus the limited compatibility is thought to arise from intramolecular interactions within the cellulose mixed benzyl ethers. The treatment of cellulose mixed derivatives as copolymers and the potential use of intramolecular effects in cellulose derivative blending is discussed. © 1995 John Wiley & Sons, Inc.