Increase Of PCL Content Research Articles

Hydrolytic Degradation of Double Crystalline PPDX‐b‐PCL Diblock Copolymers

AbstractSummary: The degradation behavior of the diblock copolymers PPDX‐b‐PCL was studied under in vitro conditions, in samples with high PPDX content. Molded films were immersed in phosphate buffer solution at pH = 7.4 and 37 °C for 9 months. The samples were periodically extracted, dried and evaluated by weighing, SEC, 1H NMR, DSC, and POM. The results point out that an increase in PCL content reduced the weight loss in the diblock copolymers. 1H NMR and DSC analysis showed that degradation occurred almost exclusively in the PPDX block during the first 9 months of hydrolysis. POM results for the diblock copolymer with high PPDX content (77%) indicated the presence of some typical homo‐PPDX spherulites in the 0.8 months degraded sample when no weight loss was detected. This result demonstrated that random chain scission during the early stages of degradation can produce homo‐PPDX chains that cannot be dissolved in the hydrolysis medium because their molecular weight is still too high. It was found that a small increase in PCL content in the diblock copolymers produced a synergistic increase in the PPDX block degradation stability. This is a direct result of the inter‐digitized lamellar morphology present in the copolymers where PCL and PPDX lamellae are alternated within mixed spherulites. In view of its much higher resistance to hydrolysis, the PCL lamellae offer a barrier‐type protection to the PPDX within the copolymer. A schematic morphological model is proposed to explain the observed changes during the different degradation stages encountered by the diblock copolymers.Proposed scheme for the hydrolytic degradation process of PPDX‐b‐PCL diblock copolymers.imageProposed scheme for the hydrolytic degradation process of PPDX‐b‐PCL diblock copolymers.

Mechanical characterization of self-curing acrylic cements formulated with poly(methylmethacrylate)/poly(epsilon-caprolactone) beads.

New acrylic-based cements were formulated by replacing a mass fraction of 20% of poly(methyl methacrylate) (PMMA) powder by PMMA/poly(epsilon-caprolactone) (PCL) beads (throughout this article all compositions are given as mass fractions, unless specified otherwise). PMMA/PCL beads containing 10 and 30% PCL were synthesized by suspension polymerization. Cements were prepared by replacing part of the PMMA powder of the formulation by an equivalent mass of PMMA/PCL particles. The influence of the PCL content in the beads on the mechanical behavior was assessed by testing the cements in flexure and compression. The addition of PMMA/PCL particles with 10% PCL content resulted in a marked increase in both flexural modulus and flexural strength related to the plain PMMA beads formulation. This improvement was attributed to a decrease in the cured material porosity. Conversely, by the incorporation of beads with 30% PCL content the flexural properties decreased. This behavior was attributed to the debonding of the particles from the matrix, which was revealed by SEM images. The observed compressive yield strength decrease with the increase of PCL content in the beads was attributed to a low degree of adhesion between the heterogeneous particles and the matrix as well as to the plasticizing effect of the PCL.

Characterization of Polysiloxane Modified Polysilsesquioxane Films for Low Dielectric Applications: Microstructure, Electrical Properties and Mechanical Properties

AbstractPoly(ε-caprolactone) (PCL) / poly(siloxane-silsesquioxane) (PSQ-PSSQ) nanohybrid films were fabricated. The dielectric constant of the film was scaled down from 2.66 to 2.28 when the 30% PCL was added into poly(siloxane-silsesquioxane) matrix. The FE-SEM micrograph of poly(ε-caprolactone) / poly(siloxane-silsesquioxane) (PSQ-PSSQ) nanohybrid film shows nanoporous structure. The modulus and hardness of the film decrease with increasing film thickness. As PCL content increases, modulus and hardness of the films decreases.

Ringed spherulite morphology and compatibility in the binary blends of poly(ε-caprolactone) with ethyl cellulose

Ringed spherulite morphology of poly(ε-caprolactone) (PCL) in PCL/ethyl cellulose (EC) blends has been observed by polarizing microscopy. When EC content was less than 40% the clear and regular ringed spherulites can form at crystallization temperatures around 313 K. Differential scanning calorimetry measurements showed the melting temperatures ( T m) and the thermal crystallization temperatures ( T c) of PCL in the blends decreased while the supercooling ΔT ( ΔT= T m 0− T c) increased comparing with those of pure PCL. Such results mean that PCL and EC are partially compatible. Fourier transform infrared measurements showed that the absorption bands of hydroxyl groups in EC shift to the lower frequencies when PCL content increases, and a specific interaction exists between the carbonyl groups of PCL and the hydroxyl groups. Just the existence of a specific interaction and partial compatibility between PCL and amorphous EC improved the formation of PCL ringed spherulites in the blends.

Miscibility, morphology and tensile properties of vinyl chloride polymer and poly(?-caprolactone) blends

The miscibility, morphology and tensile properties of three blend systems of poly(e-caprolactone) (PCL) with poly(vinyl chloride) (PVC) and with two chlorinated PVCs (CPVCs) with different chlorine contents (63 wt% and 67 wt% of Cl) have been studied. Based on the shifts of single glass transition temperature, the Gordon–Taylor K parameter is calculated as a measurement of interaction strength between PCL and (C)PVCs. Higher K values are found for blends of (C)PVCs with higher chlorine content, together with the interaction χ parameters estimated from the melting point depression results. The morphology observed with polarized light microscopy shows that spherulites exist in blends rich in PCL (≥50 wt%) only. Wide angle X-ray diffraction studies indicate that the crystal structure of PCL is independent of the Cl content of (C)PVCs. The tensile properties of various blends exhibit a minimum as the PCL content increases. The elongation at break increases with increasing PCL content. © 2000 Society of Chemical Industry

Charge distributions in PC/SAN/PCL polymer blends

The formation of space charge in polycarbonate (PC)/poly (styrene-co-acrylonitrile) (SAN) blends containing poly (/spl epsiv/-caprolactone) (PCL) as a compatibilizer for improving the miscibility, has been studied by measuring spatial charge distributions. It is found that the miscibility of PC/SAN blends is improved as the PCL content increases. The amount of charge accumulated in the blends decreases when the PCL content increases to 15% by weight and then increases when the PCL content is >15% wt. The decrease of charge at the PCL content <15% wt was attributed to the combined effects of changes in conductivities and the molecular interactions at the domain interfaces. The increase of charge at the PCL content >15% wt was attributed to the trapping of charge at the amorphous and crystalline phases of PC and PCL.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characterization of the interactions in the poly(4-hydroxystyrene)/ poly(ε-caprolactone) system by inverse gas chromatography

Inverse gas chromatography has been used to measure the thermodynamic interaction between poly(4-hydroxystyrene) (P4HS) and poly(ε-caprolactone) (PCL) at 190°C. The retention behaviour of the homopolymers and three blends (0.25, 0.5 and 0.75 P4HS volume fraction) was characterized for 13 probes. The polymer-polymer interaction parameter χ 23 calculated from the Soctt-Flory-Huggins formalism showed an apparent dependence on the probes. The method based on the equation-of-state theory given by Horta et al. and a more simplified method recently proposed by Deshpande were applied to eliminate the influence of the probe on χ 23. The results of these methods were closely similar to the one obtained by melting-point depression of the PCL in the binary blends. Negative values of χ 23 confirm the miscibility of the system. A blend composition dependence of χ 23 has been found, leading to more miscible blends when the PCL content increases. This behaviour was related to the differences in the surface-to-volume ratio of both polymers.