PCL Spherulites Research Articles

Characterization and in‐vitro analysis of poly(ε‐caprolactone)‐“Jackfruit” Mucilage blends for tissue engineering applications

AbstractJackfruit mucilage (JM) obtained from the fruit, Artocarpus heterophyllus was melt blended with poly(ε‐caprolactone) (PCL). The physical properties of the blends with more than 60 wt% PCL were investigated. Depression in the equilibrium melting temperature () and the presence of extinction rings in the spherulites of PCL in the blends confirmed miscibility of the two components. The carbonyl and the COC groups of PCL and JM were responsible for the interactions as identified by Fourier transform infrared spectroscopy. The thermal stability of PCL decreased marginally in the blends with increasing JM content. The scanning electron microscopy (SEM) images indicated that no phase separation occurred. Porosity and the mechanical strength of the blends decreased with increasing JM content. Blends exposed to porcine pancreatic lipase showed enzymatic degradation of JM but not PCL and SEM images showed holes in the sample indicative of selective degradation of JM. Cell growth inhibition technique using the L929 fibroblasts cells showed the degree of inhibition was dependent on the increasing JM content in the blends. Blends with low JM content have the potential to be used for increased cell viability while blends with high JM content can be used for the treatment of cancer.

Effect of loadings of nanocellulose on the significantly improved crystallization and mechanical properties of biodegradable poly(ε-caprolactone)

Biodegradable poly(ε-caprolactone) (PCL)/nanocellulose (NC) nanocomposites were prepared using solvent-free melt processing techniques with various NC contents. Both the nonisothermal and isothermal melt crystallization processes of PCL/NC nanocomposites were significantly accelerated by adding NC. The nonisothermal melt crystallization peak temperature obviously increased from 18.8 °C for neat PCL to 30.9 °C for the PCL/NC nanocomposite with 10 wt% NC content at a cooling rate of 10 °C min−1; moreover, the half-time isothermal crystallization at 40 °C significantly decreased from 12.2 min for neat PCL to 2.0 min. Apparently, NC enhanced PCL's crystallization rate. The crystalline morphology study confirmed the increased nucleation density of PCL spherulites, indicating the role of NC as an efficient nucleating agent. Moreover, the loading of NC did not change the crystal structure of PCL, and with increase in NC content, the Young's modulus and yield strength increased; however, the elongation-at-break and the breaking strength decreased. Compared with pure PCL, the thermomechanical properties of PCL/NC nanocomposites were significantly improved. These biodegradable PCL/NC nanocomposites showed excellent crystallization capabilities and tailored mechanical properties, thus proving their potential as a substitute for traditional commercial plastics.

Chiral Nucleating Agents Affecting the Handedness of Lamellar Twist in the Banded Spherulites in Poly(ε-Caprolactone)/Poly(Vinyl Butyral) Blends.

Chiral silica, which acts as a nucleating agent of poly(ε-caprolactone) (PCL), was demonstrated to induce excess handedness of lamellar twist in the banded spherulites of PCL blended with poly(vinyl butyral). The d- and l-forms of silica enhanced the right- and left-handed twists, respectively. The influences of chiral silica on the twist handedness were statistically significant. These results indicate that the handedness of twisting can be controlled upon primary nucleation. The organic substances used as chiral templates of silica had no effect on the handedness; silica was shown to govern the handedness. The possible mechanisms of the chirality transfer are discussed.

Phenotype Regulation of Smooth Muscle Cells Through Facial Crystallization of Poly(ɛ-Caprolactone)

Phenotype conversion of smooth muscle cells (SMCs) plays a key role in the formation of atherosclerosis. Understanding how SMCs respond to a micro/nano-topology and elucidating the cellular mechanism of phenotype conversion is critical to the atherosclerosis treatment. Herein, we prepared poly(ɛ-caprolactone) (PCL) spherulites with a radius more than 350 μm for the studying of radial microstructure influence on SMCs behaviors. We found that on the PCL spherulitic films, SMCs grew aligning the radial direction of PCL spherulites, overexpressed α-SMA gene than OPN gene, and preferred contractile phenotype. FAK signaling pathway and ROCK1 signaling pathway both contributed to the contractile phenotype maintenance of SMCs. This work illustrated the feasibility of spherulites in regulating SMCs behaviors, and elucidated the mechanism how SMCs respond to a radial micro/nano-topology. This research may provide theoretical basis for the atherosclerosis formation and treatment.

Poly(3-hexylthiophene) nanowhiskers filler in poly(ε-caprolactone) based nanoblends as potential bioactive material

The inclusion of a polymeric nanofiller with distinctive optoelectronic properties within a well-processable polymer matrix has enabled the fabrication of a wide range of functional materials. However, most of recent works focused on the characterization of the entire composite, without taking into account the effects of the matrix in the morphology of the nanofillers. This paper reports a comprehensive study about the dispersion of poly(3-hexylthiophene) (P3HT) nanowhiskers (NWs) within a poly(ε-caprolactone) (PCL) matrix, yielding a structurally defined nanoblend that could be applied as photoactive material for tissue engineering. NW formation through P3HT crystallization/aggregation was investigated within anisole solutions of PCL by UV-vis spectroscopy, while the excitation bandwidth and the resonant Coulomb coupling constant were calculated by using a non-isothermal variation of the Avrami’s law. The presence of PCL was demonstrated to increase the rate of P3HT crystallization, and determined the assembly of well-defined NWs, featuring a larger conjugation length than that characteristic of nanocrystals obtained from pure P3HT. P3HT-PCL films presented the semicrystalline morphology typical of PCL, with aggregates of P3HT NWs mainly concentrating at the boundaries of PCL spherulites, and thus forming a semiconducting polymer network that expands through a biodegradable polymer matrix.

Development of poly(ε‐caprolactone)/pine resin blends: Study of thermal, mechanical, and antimicrobial properties

Blends of poly(ε‐caprolactone) (PCL) with pine resin, an extract from the plant Pinus caribaea—Hondurensis was prepared by melt mixing in mass ratios from 90/10 to 50/50. The thermal, crystallization, morphological, and mechanical properties of the blends were studied by differential scanning calorimetry, Fourier transform infrared spectroscopy, polarized optical microscopy, scanning electron microscopy, and tensile test. Enzymatic degradation of the blends was investigated using porcine pancreatic and Candida rugosa lipase. Antimicrobial activity of the blends was tested against four strains of bacteria; Staphylococcus aureas, Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa using the zone inhibition method. Miscibility of the blends was confirmed by the depression in the equilibrium melting temperature () of PCL estimated from Hoffman–Weeks plot and the presence of extinction rings in the spherulites of blended PCL. Interactions between the two components involved the carbonyl and the C‐O‐C groups. The tensile strength of the blends with low pine resin content was comparable to PCL but decreased with higher pine gum content. Enzymatic degradation of the blends increased with increasing pine resin content. The blends showed antimicrobial property with all the bacteria except E. coli. The developed biomaterial shows promising candidacy in medical applications. POLYM. ENG. SCI., 59:E32–E41, 2019. © 2018 Society of Plastics Engineers

Crystallization and Segregation Behavior at the Submicrometer Scale of PCL/PEG Blends

The crystallization and segregation behavior of immiscible polycaprolactone/poly(ethylene glycol) PCL/PEG (50/50) blends was investigated using mainly resonance-enhanced atomic force microcopy coupled with infrared spectroscopy (AFM-IR) which allows a spatial resolution of the order of 30–50 nm. Chemical infrared images of the blends at different scales highlight their island-like spherulitic structures. The nanoscale IR spectra on both sides of the spherulitic interfaces are different. The polymer segregation mechanism of the blend in the spherulitic structure is also investigated in which PEG is rejected outside of PCL spherulites at low crystallization temperature (30 °C) while it is rejected in the form of small nodules with a dimension in the order of few micrometers, inside of PCL spherulites at higher crystallization temperature (40 °C) due to the presence of an upper critical solution temperature (UCST).

Disclosing the crystallization behavior and morphology of poly(ϵ‐caprolactone) within poly(ϵ‐caprolactone)/poly(l‐lactide) blends

AbstractIn this work, the effect of poly(l‐lactide) (PLLA) components on the crystallization behavior and morphology of poly(ϵ‐caprolactone) (PCL) within PCL/PLLA blends was investigated by polarized optical microscopy, DSC, SEM and AFM. Morphological results reveal that PCL forms banded spherulites in PCL/PLLA blends because the interaction between the two polymer components facilitates twisting of the PCL lamellae. Additionally, the average band spacing of PCL spherulites monotonically decreases with increasing PLLA content. With regard to the crystallization behaviors of PCL, the crystallization ability of PCL is depressed with increase of the PLLA content. However, it is interesting to observe that the growth rate of PCL spherulites is almost independent of the PLLA content while the overall isothermal crystallization rate of PCL within PCL/PLLA blends decreases first and then increases at a given crystallization temperature, indicating that the addition of PLLA components shows a weak effect on the growth rate of the PCL but mainly on the generation of nuclei. © 2018 Society of Chemical Industry

Enhanced crystallization rate of biodegradable poly(ε-caprolactone) by cyanuric acid as an efficient nucleating agent

The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(e-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.

Crystallization kinetics and morphology of biodegradable Poly(ε-caprolactone) with chain-like distribution of ferroferric oxide nanoparticles: Toward mechanical enhancements

Distribution of nanoparticles in nanocomposites is one of the most important roles to design unique morphologies and properties; however, up to now, it is still very difficult to control distribution of nanoparticles in polymer matrix. Here we show a simple approach to fabricate ferroferric oxide (Fe3O4) nanoparticles with controllable chain-like distribution in poly(ε-caprolactone) (PCL) by a magnetic self-organization. Randomly distributed Fe3O4 nanoparticles can be polarized and the interparticle dipole-dipole attraction drives their assembly into linear chains in an external magnetic field. The accelerated PCL crystallization happens at low Fe3O4 loadings, while the retardation to crystallization happens at high Fe3O4 loadings, especially for the samples with chain-like structures. Furthermore, PCL spherulites are also arranged into chain-like structures by the Fe3O4 nanoparticle chains. As a result, the PCL/Fe3O4 nanocomposites with chain-like structures exhibit higher storage modulus, Young's modulus and tensile strength than that of the corresponding nanocomposites with random distribution of Fe3O4 nanoparticles, indicating mechanical enhancements.

Biodegradable polymers for marine antibiofouling: Poly(ε-caprolactone)/poly(butylene succinate) blend as controlled release system of organic antifoulant

Polymer carrier is critical for the controlled release of antifoulant in marine anti-biofouling. We have prepared biodegradable polymer blend consisting of poly(ε-caprolactone) (PCL) and poly(butylene succinate) (PBS) and used it as carrier of organic antifoulant (4,5-dichloro-2-octyl-isothiazolone). Polarizing optical microscope (POM) and differential scanning calorimetry (DSC) measurements show that the spherulite size of PCL decreases and its crystallinity slightly varies as PBS fraction increases leading the interfacial regions between PCL and PBS spherulites to increase in the total area. Our studies reveal that such amorphous interfacial regions allow the blend to degrade at a constant rate and the antifoulants to be uniformly dispersed in the blend. The antifoulants are released at a constant rate as the blend degrades in marine environment, which can be modulated by the blend composition. Marine field tests demonstrate that such a system has good marine anti-biofouling performance.

Influence of film thickness on the crystalline morphology of a copolyesterurethane comprising crystallizable poly(ɛ-caprolactone) soft segments.

In this work, a model approach to investigate changes in crystalline morphology during heating/cooling procedures in the context of programming and induction of the shape-memory effect is presented. Atomic-force microscopy (AFM) was performed to investigate the variations in poly(ɛ-caprolactone) (PCL) crystalline morphology in nm thin films on a silicon substrate and a film with 20 μm thickness, prepared from a copolyesterurethane (named PDLCL) consisting of crystallizable poly(ω-pentadecalactone) (PPDL) hard segments and crystallizable PCL segments forming switching domains. PCL crystals in switching domains melted/recrystallized repeatedly during heating/cooling cycles between 20 and 70 °C, while no evident variation in PPDL crystals forming hard domains was observed. When film thickness was 20 nm, PCL edge-on lamellae were observed, confined in the phase-separated morphology. Flat-on PCL lamellae, which broke out from the previous phase-separated morphology, were obtained at a film thickness of 170 nm. In contrast, large PCL spherulites were observed in the 20 μm thick film. PCL crystalline morphology in PDLCL as well as the competition between crystallization and phase separation can be tailored by the film thickness and the substrate. Such AFM investigations on thin films can be a helpful approach for predicting the crystal morphology in micro-/nanoscaled objects.

Synthesis, characterization, and crystallization of biodegradable poly(ε-caprolactone)-poly(L-lactide) diblock copolymers

AbstractThree diblock copolymers of PCL6k-PLLA2k, PCL6k-PLLA4k, and PCL6k-PLLA6k were prepared and their crystallization behaviors were investigated. The molecular weights of the copolymers calculated from 1H nuclear magnetic resonance spectra were equivalent to the designed molecular weights. The gel permeation chromatography spectra of the copolymers showed one peak, which revealed that the copolymers were monodisperse. The crystallization capability of poly(ε-caprolactone) (PCL) decreased and that of poly(L-lactide) (PLLA) increased when the molecular weight of the PLLA block was increased from 2k to 6k. PCL spherulites in the PCL6k-PLLA2k copolymer film were smaller than those in PCL6k-PLLA4k or PCL6k-PLLA6k copolymer film. PCL spherulites in the PCL6k-PLLA2k copolymer film grew fastest within all three diblock copolymers. An obvious phase separation phenomenon was observed on the surface of PCL6k-PLLA6k copolymer film in atomic force microscopy images.

Morphological regimes of poly(ε-caprolactone)/octaisobutyl polyhedral oligosilsesquioxane composite films in relation to film composition and thickness

The morphological evolution of poly(e-caprolactone) (PCL)/octaisobutyl polyhedral oligomeric silsesquioxane (IBUPOSS) films was analyzed using scanning electron microscopy (SEM) and polarized optical microscopy (POM). The morphologies of the blend films with PCL/IBUPOSS mass ratios of 95:5 to 50:50 were discussed according to decomposition mechanism in relation to film composition and thickness. In addition to the morphological regime for films with lower IBUPOSS loadings, in which the growth of PCL spherulites was nearly independent on the presence of fine IBUPOSS aggregates, two new morphological regimes were observed for the films with higher IBUPOSS loadings: (1) thicker blend films exhibited a rich dynamics, giving rise to a trilayer structure and (2) the decomposition of thinner films was induced by the kinetically controlled growth of IBUPOSS aggregates. By varying the thickness and the composition of the blend films, the current study provides important new insight into the rich phase behavior of nanoparticle-filled polymer films.

Peptide‐poly(ε‐caprolactone) biohybrids by grafting‐from ring‐opening polymerization: Synthesis, aggregation, and crystalline properties

AbstractWell‐defined peptide‐poly(ε‐caprolactone) (Pep‐PCL) biohybrids were successfully synthesized by grafting‐from ring‐opening polymerization (ROP) of ε‐caprolactone (CL) using designed amine‐terminated sequence‐defined peptides as macroinitiators. MALDI‐TOF‐MS and 1H NMR analyses confirmed the successful attachment of peptide to the PCL chain. The gel permeation chromatography (GPC) measurement showed that the Pep‐PCL biohybrids with controllable molecular weights and low polydispersities (PDI <1.5) were obtained by this approach. The aggregation of Pep‐PCL hybrid molecules in THF solution resulted in the formation of micro/nanospheres as confirmed through FESEM, TEM, and DLS analyses. The circular dichroism study revealed that the secondary structure of peptide moiety was changed in the peptide‐PCL biohybrids. The crystallization and melting behavior of Pep‐PCL hybrids were somewhat changed compared with that of neat PCL of comparable molecular weight as revealed by DSC and XRD measurements. In Pep‐PCL biohybrids, extinction rings were observed in the PCL spherulites, in contrast with the normal spherulite morphology of the neat PCL. There was a substantial decrease (4–5 folds) in the spherulitic growth rate after the incorporation of peptide moiety at the end of PCL chain as measured by polarizing optical microscopy. Pseudomonas lipase catalyzed enzymatic degradation was studied for Pep‐PCL hybrids and neat PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Miscibility Determination in Poly(ϵ-caprolactone)/Poly(Vinyl Formal) Blend by Equilibrium Melting Temperature and Spherulite Morphology

Miscibility of poly(ϵ-caprolactone), (PCL), containing 1, 5, and 10 wt.% poly(vinyl formal) (PVF) blends was investigated by polarized optical microscopy (POM), atomic force microscopy (AFM), and differential scanning calorimetry (DSC) for spherulitic morphology and equilibrium melting temperature (T°m, via Hoffman-Weeks plot). The T°m of PCL in the blends was similar to that of pure PCL, indicating immiscibility. Isothermally, melt crystallized virgin PCL between 30°C and 50°C showed spherulitic morphology with negative birefringence, Maltese cross, and without extinction rings. The nucleation and growth rates of PCL spherulites were found to be dramatically reduced with the addition of PVF. Extinction rings and a change in the sign of the birefringence of the PCL spherulites were observed and were found to be dependent on blend composition and crystallization temperature. The presence of a ring pattern in spherulites was an indication of miscibility between the two polymers that had failed to be detected by thermal methods. The formation of a ring pattern is discussed in terms of lamella twisting originating from a change in the crystallization mechanism.

Ring‐banded spherulites in PCL and PCL/MWCNT solution‐casting films and effect of compressed CO2 on them

AbstractThe ring‐banded spherulites in poly(ε‐caprolactone) (PCL) solution‐casting films in the absence and presence of multi‐walled carbon nanotube (MWCNT) are studied by atomic force microscopy (AFM), polarized optical microscopy (POM), transmission electron microscopy (TEM), and scanning electronic microscopy (SEM). The results indicate that birefringent ring‐banded spherulites of PCL can grow from solution below 50 °C, and the temperature is much lower than that from pure PCL melt. We also find out that the presence of MWCNT apparently widen the temperature range of forming ring‐banded structure. Furthermore, the mechanism for the ring‐banded structure forming is studied, and it is attributed to the twisting of lamellae crystals, and the driving force is suggested including the deflexion of lamellae bundles. In addition, effect of compressed CO2 on the morphology of PCL and PCL/MWCNT solution‐casting film is also investigated, and the results reveal that both PCL and PCL/MWCNT films undergo recrystallization with the treatment of compressed CO2 and accordingly, the related properties can be adjusted. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 784–792, 2009

Relationship between Fracture Mechanism and Microstructure in PLA/PCL Polymer Blends

PLA/PCL and PLA/PCL/LTI blends were developed to improve the fracture properties of biodegradable PLA. LTI was blended to improve the miscibility of PLA and PCL. It was shown that the fracture toughness values were dramatically increased due to LTI addition. SEM results also exhibited that PCL spherulites decreases due to LTI addition and therefore, void formation is reduced and local stress concentration is suppressed, resulting in the improvement of the toughness values. The improved miscibility is also closely related to the enhancement of ductile deformation; as a result, the fracture toughness is increased.

Crystallization behavior of poly(ϵ‐caprolactone) in poly(ϵ‐caprolactone) and poly(vinyl methyl ether) mixtures

AbstractThe morphological development and crystallization behavior of poly(ϵ‐caprolactone) (PCL) in miscible mixtures of PCL and poly(vinyl methyl ether) (PVME) were investigated by optical microscopy as a function of the mixture composition and crystallization temperature. The results indicated that the degree of crystallinity of PCL was independent of the mixture composition upon melt crystallization because the glass‐transition temperatures of the mixtures were much lower than the crystallization temperature of PCL. The radii of the PCL spherulites increased linearly with time at crystallization temperatures ranging from 42 to 49°C. The isothermal growth rates of PCL spherulites decreased with the amount of the amorphous PVME components in the mixtures. Accounting for the miscibility of PCL/PVME mixtures, the radial growth rates of PCL spherulites were well described by a kinetic equation involving the Flory–Huggins interaction parameter and the free energy for the nuclei formation in such a way that the theoretical calculations were in good agreement with the experimental data. From the analysis of the equilibrium melting point depression, the interaction energy density of the PVME/PCL system was calculated to be −3.95 J/cm3. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Miscibility, melting and crystallization of poly(ε-caprolactone) and poly (vinyl formal) blend

Solution cast blends of poly(e-caprolactone) [PCL] and poly(vinyl formal) [PVF] from dichloromethane was investigated for miscibility by Differential Scanning Calorimetry [DSC], Fourier Transform Infrared Spectroscopy [FTIR] and optical microscopy. Melting (Tm) and crystallization (Tc) temperatures were for the PCL fraction while the glass transition temperature (Tg) was for PVF fraction in the blends. Blends with 20 wt% and less PCL showed a depression in Tm and Tc. Depression in Tc indicated that during the non-isothermal crystallization process, the presence of PVF decreased the PCL segments migrating to the crystallite-melt interface thus reducing the nucleation rate, growth rate and the thickness of the lamella resulting in a depressed Tm. Crystallinity (Xc) decreased gradually with decreasing content of PCL in the blend and was due to the dilution of PCL by PVF. A depressed Tg was observed for 10 wt% PCL blend and remained the same for all other blend compositions. These observations suggested that this blend system has very low degree of miscibility. The degree of miscibility increased at low polyester concentration. FTIR spectra of the blends with low polyester concentrations showed changes in the C=O, O-H and C-O-C regions in the blended PVF and PCL spectra. Optical microscopy showed phase separation in the melt and in the PCL spherulites.