PCL Composites Research Articles

Qualitative assessment of nanofiller dispersion in poly(ε-caprolactone) nanocomposites by mechanical testing, dynamic rheometry and advanced thermal analysis

A comprehensive overview of available methods for assessing nanofiller dispersion is presented for a wide range of layered silicate-based poly(ε-caprolactone) (PCL) nanocomposites. Focusing on their respective strengths and weaknesses, rheological, mechanical and thermal characterization approaches are evaluated in direct relation to morphological information. Pronounced changes in the rheological and mechanical properties of the materials are only observed for nanocomposites displaying the highest nanofiller dispersion levels, as confirmed by an innovative and highly reliable thermal analysis approach based on quasi-isothermal crystallization. As such, the data obtained from the different methods also allow a detailed investigation of the crucial factors affecting nanofiller dispersion, evidencing the importance of specific matrix/filler interactions and the need for proper melt processing conditions when targeting significant property enhancements. Finally, the wide potential of the developed methodologies for the characterization of polymeric nanocomposites in general is illustrated by an extension to carbon nanotube-based PCL composites, unambiguously demonstrating their complementarity and broad applicability.

The effect of scaffold composition on the early structural characteristics of chondrocytes and expression of adhesion molecules

Previously we demonstrated that chondrocyte ECM synthesis and mitotic activity was dependent on scaffold composition when cultured on uncoated PCL scaffolds (pPCL) or PCL composites containing hyaluronan (PCL/HA), chitosan (PCL/CS), fibrin (PCL/F), or collagen type I (PCL/COL1). We hypothesized that initial cell contact with these biomaterials results in ultrastructural changes and alters CD44 and integrin beta1 expression. The current study was designed to investigate the early ultrastructural responses of chondrocytes on these scaffolds and expression of CD44 and integrin beta1. A common observation 1 h after seeding was the abundance of cell processes. Different types of cell processes occurred in different areas of the same cell and on different cells within the same composite. Chondrocytes seeded onto PCL/CS had the greatest cell surface enhancement. PCL/HA promoted CD44 expression and almost spherical cells with a low degree of surface enhancement. PCL/COL1 enabled continuing expression of integrin beta1 and CD44. In contrast, cells in PCL/CS, PCL/F and pPCL promoted elliptic cells with a higher degree of surface enhancement and no prolonged CD44 and integrin beta1 expression. A strong variability of cell surface processes indicated either reparative or degenerative adaptation to the artificial environment. Interestingly, we found initial integrin beta1 expression in all composite scaffolds, but not in pPCL although this promoted strong adhesiveness as indicated by the formation of stress fibers. In conclusion, chondrocytes respond to biomaterials early after implantation by altering ultrastructural characteristics and expression of CD44 and integrin beta1.

Nonisothermal crystallization kinetics and thermomechanical properties of multiwalled carbon nanotube‐reinforced poly(ε‐caprolactone) composites

AbstractBACKGROUND: The technological development of poly(ε‐caprolactone) (PCL) is limited by its short useful lifespan, low modulus and high crystallinity. There are a few papers dealing with the crystallization behavior of carbon nanotube‐reinforced PCL composites. However, little work has been done on the crystallization kinetics of melt‐compounded PCL/multiwalled carbon nanotube (MWNT) nanocomposites. In this study, PCL/MWNT nanocomposites were successfully prepared by a simple melt‐compounding method, and their morphology and mechanical properties as well as their crystallization kinetics were studied.RESULTS: The MWNTs were observed to be homogeneously dispersed throughout the PCL matrix. The incorporation of a very small quantity of MWNTs significantly improved the storage modulus and loss modulus of the PCL/MWNT nanocomposites. The nonisothermal crystallization behavior of the PCL/MWNT nanocomposites exhibits strong dependencies of the degree of crystallinity (Xc), peak crystallization temperature (Tp), half‐time of crystallization (t1/2) and Avrami exponent (n) on the MWNT content and cooling rate. The MWNTs in the PCL/MWNT nanocomposites exhibit a higher nucleation activity. The crystallization activation energy (Ea) calculated with the Kissinger model is higher when a small amount of MWNTs is added, then gradually decreases; all the Ea values are higher than that of pure PCL.CONCLUSION: This paper reports for the first time the preparation of high‐performance biopolymer PCL/MWNT nanocomposites prepared by a simple melt‐compounding method. The results show that the PCL/MWNT nanocomposites can broaden the applications of PCL. Copyright © 2008 Society of Chemical Industry

Nanocomposites based on poly(ε-caprolactone) and the montmorillonite treated with dibutylamine-terminated ε-caprolactone oligomer

Dibutylamine-terminated ε-caprolactone oligomers (CLOs: CLOL, CLOM, and CLOH) with number–averaged molecular weight (Mn), 500, 1300, and 2200, respectively, were synthesized by the ring-opening polymerization of ε-caprolactone initiated by 2-(dibutylamino)ethanol in the presence of tin(II) 2-ethylhexanoate. Nanocomposites based on poly(ε-caploractone) (PCL) and the caprolactone oligomer-treated montmorillonites (CLO-Ms: CLOL-M, CLOM-M, and CLOH-M) were prepared by melt intercalation method. The XRD and TEM analyses of the PCL composites revealed that the extent of exfoliation of the clay platelets increased with increasing molecular weight of the used CLOs. Tensile strength and modulus of the PCL/CLO-M composites increased with increasing molecular weight of the CLO and increasing inorganic content. The tensile modulus of the PCL/CLOH-M nanocomposite with inorganic content 5.0 wt % was three times higher than that of control PCL. Among the PCL/CLO-M composites, the PCL/CLOM-M composite had the highest crystallization temperature and melting temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Thermal and mechanical behavior of injection molded Poly(3-hydroxybutyrate)/Poly(epsilon-caprolactone) blends

Aiming the development of high-performance biodegradable polymer materials, the properties and the processing behavior of poly(3-hydroxybutyrate), P(3HB), and their blends with poly(epsilon-caprolactone), PCL, have been investigated. The P(3HB) sample, obtained from sugarcane, had a molecular weight of 3.0 x 10(5) g.mol¹, a crystallinity degree of 60%, a glass transition temperature (Tg), at - 0.8 °C, and a melting temperature at 171 °C. The molecular weight of PCL was 0.8 x 10(5) g.mol-1. Specimens of 70/30 wt. (%) P(3HB)/PCL blends obtained by injection molding showed tensile strength of 21.9 (± 0.4) MPa, modulus of 2.2 (± 0.3) GPa, and a relatively high elongation at break, 87 (± 20)%. DSC analyses of this blend showed two Tg´s, at - 10.6 °C for the P(3HB) matrix, and at - 62.9 °C for the PCL domains. The significant decrease on the Tg of P(3HB) evidences a partial miscibility of PCL in P(3HB). According to the Fox equation, the new Tg corresponds to a 92/8 wt. (%) P(3HB)/PCL composition.

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by 1H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.

Biodegradation of aliphatic polyester composites reinforced by abaca fiber

The composites of aliphatic polyesters (poly( ϵ-caprolactone) (PCL), poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV), poly(butylene succinate) (PBS), and poly(lactic acid) (PLA)) with 10 wt.% untreated or acetic anhydride-treated (AA-) abaca fibers were prepared and their biodegradability was evaluated by the soil-burial test. In case of PCL composites, the presence of untreated abaca or AA-abaca did not pronouncedly affect the weight loss because PCL itself has a relatively high biodegradability. However, the addition of abaca fibers caused the acceleration of weight loss in case of PHBV and PBS composites. Especially, when untreated abaca was used, the PHBV and PBS composite specimens were crumbled within 3 months. This result is a marked contrast to the fact that neat PHBV and PBS specimens retain the original shape even after 6 months. Although no weight loss was observed for neat PLA and PLA/AA-abaca composite, the PLA/untreated abaca composite showed ca. 10% weight loss at 60 days, which was caused by the preferential degradation of the fiber.

Composite cell support membranes based on collagen and polycaprolactone for tissue engineering of skin

The preparation and characterisation of collagen:PCL composites for manufacture of tissue engineered skin substitutes and models are reported. Films having collagen:PCL (w/w) ratios of 1:4, 1:8 and 1:20 were prepared by impregnation of lyophilised collagen mats by PCL solutions followed by solvent evaporation. In vitro assays of collagen release and residual collagen content revealed an expected inverse relationship between the collagen release rate and the content of synthetic polymer in the composite that may be exploited for controlled presentation and release of biopharmaceuticals such as growth factors. DSC analysis revealed the characteristic melting point of PCL at around 60°C and a tendency for the collagen component, at high loading, to impede crystallinity development within the PCL phase. The preparation of fibroblast/composite constructs was investigated using cell culture as a first stage in mimicking the dermal/epidermal structure of skin. Fibroblasts were found to attach and proliferate on all the composites investigated reaching a maximum of 2×10 5/cm 2 on 1:20 collagen:PCL materials at day 8 with cell numbers declining thereafter. Keratinocyte growth rates were similar on all types of collagen:PCL materials investigated reaching a maximum of 6.6×10 4/cm 2 at day 6. The results revealed that composite films of collagen and PCL are favourable substrates for growth of fibroblasts and keratinocytes and may find utility for skin repair.

Poly(∊-Caprolactone) Composites Reinforced with Short Abaca Fibres

The tensile properties of poly( ∊-caprolactone) (PCL) composites reinforced with short abaca fibres (length ca. 5 mm) prepared by melt mixing and subsequent injection molding were investigated and compared with PCL composites reinforced with glass fibres (GF). The influence of fibre content and surface esterification of the natural fibre on the tensile properties was evaluated. The tensile strength and moduli of all the PCL/abaca composites increased with increasing fibre content. All the PCL/abaca composites had a higher tensile strength than the PCL/GF composites when the fibre weight fraction was the same. The tensile strength of the PCL/abaca composites was improved by surface esterification of the abaca with acetic anhydride or butyric anhydride in the presence of pyridine, because of the increase in the interfacial adhesiveness between the matrix polyester and the esterificated fibre, as is obvious from the SEM photographs.

Composites consisting of poly(ε-caprolactone) and cellulose fibers directly molded during polymerization by yttrium triflate

Composite samples consisting of poly(e-caprolactone) (PCL) and cellulose fibers (CF) were prepared by the direct molding method during polymerization from e-caprolactone (CL) monomers. CL liquid was mixed with yttrium triflate as a catalyst and 2-propanol as an initiator. CF was easily added to CL liquid and was homogeneously mixed with CL liquid by this method. The mixture was put into a plastic tube. Heating temperature varied from 60 to 120 °C and heating time varied from 6 to 48 h. CF content varied from 0 to 30 wt%. After cooling, the sample was removed from the tube and cut into a column shaped specimen. PCL composites with CF dispersed homogeneously were obtained. The mechanical properties such as elastic modulus and strength of these PCL composites with CF were measured by compression test using the above specimen. The maximum values of modulus and strength of composite samples are the maximum values 654 and 13 MPa, when fiber content was 34% and these values are greater than those of PCL samples without CF. The biodegradability of PCL composites in an aqueous medium with commercial compost was evaluated measuring the biochemical oxygen demand (BOD). The biodegradability of composite samples was not affected by the presence of CF.

Microcomposites of Poly(ε‐caprolactone) and Poly(methyl methacrylate) Prepared by Suspension Polymerization in the Presence of Poly(ε‐caprolactone) Macromonomer

AbstractPoly(methyl methacrylate)‐poly(ε‐caprolactone) (PMMA/PCL) microparticles were synthesized by suspension polymerization of methyl methacrylate in the presence of PCL. The incorporation of a small amount of a macromonomer, methacryloyl‐terminated PCL (M‐PCL), into the reaction mixture, led to the formation of grafted systems, namely PMMA‐g‐PCL/PCL. The synthesis of the macromonomer and its characterization by nuclear magnetic spectroscopy (1H NMR) is described. The role of M‐PCL as an effective compatibilizing agent in the composite was investigated. PMMA/PCL and PMMA‐g‐PCL/PCL composites were fully characterized by 1H NMR, gel permeation chromatography (GPC) and thermal analysis, including thermogravimetric analysis (TGA), conventional differential scanning calorimetry (DSC), modulated DSC (MDSC) and dynamic mechanical thermal analysis (DMTA). Finally, the morphology of the prepared systems was investigated by scanning electron microscopy (SEM). The addition of compatibilizing agent led the formation of a more homogeneous microcomposite with improved mechanical properties.SEM picture of PMMA‐g‐PCL/PCL composite surface.magnified imageSEM picture of PMMA‐g‐PCL/PCL composite surface.