Fraction Of PCL Research Articles

Polymer blends of poly( ϵ-caprolactone) and poly(vinyl methyl ether) – thermal properties and morphology

We report on thermal properties and the phase behaviour of polymer blends comprising poly( ϵ-caprolactone) (PCL) and poly(vinyl methyl ether) (PVME). The blends were subjected to different thermal histories. In all cases, the fraction of PCL, that crystallizes in the blends, increases slightly up to 30% content of PVME. Crystallization rates of PCL are found markedly reduced in blends as compared to neat PCL. Ring-banded spherulites develop during isothermal crystallization. Radial growth rates of spherulites decrease exponentially with increasing PVME content up to approximately 40% of PVME. At higher PVME contents non-exponential decrease was observed. Melting points of PCL in blends were determined applying a step-wise annealing procedure. The glass transition temperatures of the blends reveal formation of PVME-rich phases even after rapid quenching of the homogeneous melt owing to crystallization of PCL. Lower critical solution temperature behaviour of the melts could be determined tentatively by optical inspection. The homogeneous melt phase-separates above approximately 190°C.

Enzymatic degradation of poly(ε-caprolactone)/poly( dl-lactide) blends in phosphate buffer solution

Blend films of poly(ε-caprolactone) (PCL) and poly( dl-lactide) (PDLLA) with 0.5 weight fraction of PCL were prepared by means of solution casting and their degradation behavior was studied in phosphate buffer solution containing Pseudomonas (PS) lipase. Enzymatic degradation of the blend films occurred continuously within the first 6 days and finally stopped when the film weight loss reached 50%, showing that only PCL in the blends degraded under the action of PS lipase in the buffer solution. These results indicate the selectivity of PS lipase on the promotion of degradation for PCL and PDLLA. The thermal properties and morphology of the blend films were investigated by differential scanning calorimetry, wide-angle X-ray diffraction and scanning electron microscopy (SEM). The morphology resulting from aggregate structures of PCL in the blends was destroyed in the enzymatic degradation process, as observed by SEM. These results confirm again the enzymatic degradation of PCL in the blends in the presence of PS lipase.

A comparison between the morphology of semicrystalline polymer blends of poly(ε-caprolactone)/poly(vinyl methyl ether) and poly(ε-caprolactone)/(styrene-acrylonitrile)

The morphology of polymer blends of poly(ε-caprolactone) (PCL) and poly(vinyl methyl ether) (PVME) is compared with that of PCL and a random copolymer of styrene and acrylonitrile (SAN). The main objective is to determine the influence of the glass transition temperature of the amorphous component ( T g,a) on the morphology of the semicrystalline polymer blends. These blends represent the two extreme cases corresponding to T c < T g,a, where T c is the crystallization temperature. The morphology of these blends, with PVME and SAN representing the amorphous components, have been studied by small angle X-ray scattering. For both blends the long period increases with the addition of amorphous polymer, which is a strong indication for an interlamellar morphology. D.s.c. experiments, including enthalpy relaxation, are used to investigate the crystallinity and the interphases. The overall amount of crystallinity in both blends decreases with increasing content of amorphous polymer. However, the fraction of PCL that crystallizes decreases in PCL/SAN and increases slightly in PCL/PVME. Apparently, the addition of the low T g,a PVME improves the crystallization of PCL in accordance with a simple Gamblers Ruin Model type argument. The high T g,a of SAN means this does not occur in PCL/SAN blends. Conventional d.s.c. experiments show an interphase of pure amorphous PCL in PCL/SAN blends and enthalpy relaxation experiments demonstrate its presence in PCL/PVME blends as well.

Time-resolved SAXS study of morphological change in a binary blend of poly(iε-caprolactone) and polystyrene oligomer

The process of morphology formation in the blend was studied at various compositions and crystallization temperatures. It is demonstrated that phase separation takes place simultaneously with the crystallization of poly(e-caprolactone) (PCL). The results ate interpreted with a combination of the paracrystalline lattice model developed by Hosemann and the two-phase model developed by Debye and Bueche. The morphological parameters such as long spacing and correlation length are evaluated as a function of time and PCL fraction

Ringed Spherulite in Binary Blends of Poly(ε-caprolactone) and ε-Caprolactone-Butadiene Diblock Copolymer

Ringed spherulites were found in binary blends of poly(ε-caprolactone) (PCL) and ε-caprolactone-butadiene diblock copolymer (PCL-b-PB), while the regularly banded structure could not be observed in an oligomeric blend of PCL and polybutadiene (PB). The repeating distance of the ring and its distribution (irregularity) were evaluated as a function of PCL homopolymer (host polymer) fraction, total PCL fraction in the blend, and crystallization temperature. The morphology and melting behavior of the PCL/PCL-b-PB blends were also investigated by small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). These results suggest that the PCL block of the copolymer takes part in the crystallization of the host polymer and is incorporated into the PCL lamellar crystal. The PB block is, as a result, forced to remain in the amorphous layer between PCL lamellae to lengthen the long spacing (alternating period of the lamella and amorphous layer). This existence of the PB block in the amorphous layer may play an important role in the lamellar twist during the course of crystallization.

Small-angle X-ray scattering study of the morphology of blends of poly(ε-caprolactone) and polystyrene oligomer

A small-angle X-ray scattering (SAXS) study was carried out to investigate the morphology of blends of poly(ε-caprolactone) (PCL) and polystyrene oligomer (PSO) when the former component was crystallized. This PCL-PSO system shows an upper critical solution temperature type of phase diagram. For blends with ф PCL < 0.8 ( ф PCL is the weight fraction of PCL), the scattering observed is the superposition of the intensities arising from the crystalline region (made up by alternate stacking of lamellae and thin amorphous layers) and from the inhomogeneity in the system (due to the crystalline regions and the amorphous domains). For blends with ф PCL > 0.8 , only scattering from the crystalline region was observed. From the SAXS curve, the lamella thickness l c, the amorphous layer thickness l a and the linear crystallinity χ c of the crystalline region were obtained on the basis of the Hosemann-Tsvankin model. The value of l c was 5.5 nm independent of composition, while l a and χ c were 8.1 nm and 0.4 for blends with ф PCL <0.8 but varied linearly with composition for blends with ф PCL > 0.8 . These parameters were also studied by the correlation function from Vonk's model.