PCL Phase Research Articles

Candida Antarctica Lipase B-assisted top-down visualization of surface morphology of poly(ε-caprolactone)/poly(ethylene oxide) blend films

A series of enzymatic degradation experiments were designed to examine the surface morphology of phase separated poly(ε-caprolactone) (PCL)/poly(ethylene oxide) (PEO) blend films. Candida antarctica Lipase B (CALB), previously reported to have superior degradation selectivity when used at low concentrations, was utilized to selectively dissect interlamellar amorphous PCL chains and therefore to reveal the crystalline region of PCL phase. Water soluble PEO can be simultaneously removed by the CALB aqueous solutions, allowing one to envision the topological features of phase separated PCL/PEO films with various blend ratios. The transition of phase-separated PCL/PEO from nucleation and growth to spinodal decomposition was fully mapped out, along with the spatial distribution and surface morphological features of the crystalline PCL phase. The morphological characteristics of PCL/PEO blend films were further correlated to their reported physicochemical properties, demonstrating the impact of microscopic structures on the macroscopic properties of given semicrystalline polymer systems.

Effect of hydrophobic modification of chitin nanocrystals on role as anti-nucleator in the crystallization of poly(ε-caprolactone)/polylactide blend

Biodegradable polymer blends filled with rod-like polysaccharide nanocrystals have attracted much attention because each component in this type of ternary composites is biodegradable, and the final properties are more easily tailored comparing to those of binary composites. In this work, chitin nanocrystals (ChNCs) were used as nanofiller for the biodegradable poly(ε-caprolactone) (PCL)/polylactide (PLA) immiscible blend to prepare ternary composites for a crystallization study. The results revealed that the crystallization behavior of PCL/PLA blend matrices strongly depended on the surface properties of ChNCs. Non-modified ChNCs and modified ChNCs played completely different roles during crystallization of the ternary systems: the former was inert filler, while the latter acted as anti-nucleator to the PCL phase. This alteration was resulted from the improved ChNC-PCL affinity after modification of ChNCs, which was due to the ‘interfacial dilution effect’ and the preferential dispersion of ChNCs. This work presents a unique perspective on the nucleation role of ChNCs in the crystallization of immiscible PCL/PLA blends, and opens up a new application scenario for ChNCs as anti-nucleator.

Phase morphology, rheological behavior and mechanical properties of supertough biobased poly(lactic acid) reactive ternary blends

Poly(lactic acid) (PLA) is one of the most promising bio-based polyester with great potential to replace for the petroleum-based polymers, which can significantly reduce greenhouse gas emissions. However, the inherent brittleness of PLA seriously restricts its broad applications. Herein, PLA/poly(ε-caprolactone) (PCL)/ethylene methyl acrylate-glycidyl methacrylate (EMA-GMA) ternary blends with different phase structures were prepared through reactive blending. The reactions between the epoxy groups of EMA-GMA and the carboxyl and hydroxyl end groups of PLA and PCL and were evidenced from the Fourier transform infrared spectroscopy, dynamic mechanical analysis and rheological results. The atomic force microscopy (AFM) images clearly revealed the formation of stack structure of the PCL and EMA-GMA minor phases in PLA/PCL/EMA-GMA (80/15/5) blend, and core-shell particle structures in PLA/PCL/EMA-GMA (80/10/10) and (80/5/15) blends. In terms of elongation at break and impact toughness, PLA/PCL/EMA-GMA (80/5/15) blend presents the best properties among all the compositions. Moreover, it also behaved excellent stiffness-toughness balance. The toughening mechanism can be ascribed to the formation of core-shell structure and the existence of interfacial adhesion in the ternary blends. This work can provide guide for the preparation and design of PLA-based partially renewable supertough materials that can compete with conventional petro-derived plastics.

Insights into Seawater Biodegradation of Sustainable Mater-Bi/Poly(ε-caprolactone)-Based Biocomposites Filled with Diisocyanate-Modified Cellulose Particles

Due to rapid economic growth, the use of plastics in almost all areas of human life has significantly increased over recent decades, leading to massive pollution. Therefore, works dealing with sustainable and biodegradable polymer materials are vital now. Herein, sustainable Mater-Bi/poly(ε-caprolactone) (PCL)-based biocomposites, filled with diisocyanate-modified cellulose particles, were prepared and subjected to 12-week seawater degradation. Changes in the chemical structure and surface wettability pointed to the increasing hydrophilicity of materials over time, which was limited by diisocyanate modifications. Only minor changes in the thermal performance of analyzed materials have been observed, pointing to the limited biodegradation of the PCL phase. The most significant effects have been related to the composite yellowing due to the filler diisocyanate modifications and surface erosion increasing its roughness. Obtained results pointing to the low degradation rate bring into question the commonly-regarded biodegradable nature of PCL material.

Effect of Polydopamine Coating of Cellulose Nanocrystals on Performance of PCL/PLA Bio-Nanocomposites.

In bio-nanocomposites with a poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) matrix with neat and polydopamine (PDA)-coated cellulose nanocrystals (CNCd), the use of different mixing protocols with masterbatches prepared by solution casting led to marked variation of localization, as well as reinforcing and structure-directing effects, of cellulose nanocrystals (CNC). The most balanced mechanical properties were found with an 80/20 PLA/PCL ratio, and complex PCL/CNC structures were formed. In the nanocomposites with a bicontinuous structure (60/40 and 40/60 PLA/PCL ratios), pre-blending the CNC and CNCd/PLA caused a marked increase in the continuity of mechanically stronger PLA and an improvement in related parameters of the system. On the other hand, improved continuity of the PCL phase when using a PCL masterbatch may lead to the reduction in or elimination of reinforcing effects. The PDA coating of CNC significantly changed its behavior. In particular, a higher affinity to PCL and ordering of PLA led to dissimilar structures and interface transformations, while also having antagonistic effects on mechanical properties. The negligible differences in bulk crystallinity indicate that alteration of mechanical properties may have originated from differences in crystallinity at the interface, also influenced by presence of CNC in this area. The complex effect of CNC on bio-nanocomposites, including the potential of PDA coating to increase thermal stability, is worthy of further study.

Interfacial distribution and compatibilization of imidazolium functionalized CNTs in poly(lactic acid)/polycaprolactone composites with excellent EMI shielding and mechanical properties

Imidazolium-functionalized polyurethane (IPU) functionalized multi-walled carbon nanotubes (CNTs) was used to control interfacial distribution and compatibilization of CNTs, and enhance electromagnetic interference (EMI) shielding and mechanical properties of poly(lactic acid)/polycaprolactone (PLA/PCL) based composites. IPU facilitated the uniformly dispersion of CNTs and induced the selectively location of CNTs at the interface and PCL phase, which is beneficial to build more effective three-dimensional network structure at the co-continuous interphase. The EMI shielding properties for the PLA/PCL/8CNT/0.8IPU composites have been evidently increased to 35.6 dB. Meanwhile, the elongation at break and the notched impact strength of the PLA/PCL/8CNT/0.8IPU composite reached 307.8 % and 51.3 kJ/m2, respectively, which are increased by 27 and 53 % of PLA/PCL/8CNT because of the compatibilization effect of IPU and the distribution of CNTs. This work presented a promising prospect of polymer-based composites with satisfactory EMI shielding and mechanical properties.

Electron-induced structural changes in flax fiber reinforced PLA/PCL composites, analyzed using the rule of mixtures

The paper presents the effect of electron treatment on the various properties of flax fibers (20 wt%; 5 mm in length) reinforced PLA/PCL (70:30) composites. To enhance the intensity of the electron-induced cross-linking reactions, triallyl isocyanurate (TAIC) as a cross-linking agent was also added (up to 3 wt%). The composites were manufactured by conventional extrusion, granulation, and injection molding techniques, and then electron irradiated at doses of up to 60 kGy. The structural changes were determined using mechanical testing (tensile strength, impact strength, dynamic mechanical analysis), gel content analysis, thermogravimetry, and differential scanning calorimetry (DSC). The modified composites were also subjected to enzymatic biodegradation and industrial composting. An important novelty aspect of the presented research, additionally to the new material composition, is the use of the rule of mixtures in the assessment of the effect of electron treatment on the interfacial interactions of dispersed PCL in the continuous phase of PLA, in the presence of flax fibers. PCL was dispersed in the PLA phase with an average phase size of a few micrometers. Based on the rule of mixtures, it was found that without TAIC, the predominantly degraded PLA phase-initiated cross-linking of the dispersed PCL phase, contributing to the interphase adhesion enhancement reflected in improved mechanical properties. To apply this model, it was required to refer to the previously published results of analogous composites with homopolymer matrix (PLA or PCL). • PCL was an effective impact modifier of flax fiber reinforced PLA /PCL composites. • The continuous phase was PLA with small-size 5 µm PCL lamellar inclusions. • Electron radiation increased the tensile strength and modulus of elasticity. • Effects of electron radiation were elucidated using the rule of mixtures. • The adhesion between PLA and PCL phases improved as a result of electron treatment.

Microstructure-Thermal Property Relationships of Poly (Ethylene Glycol-b-Caprolactone) Copolymers and Their Micelles.

The crystallinity of polymers strongly affects their properties. For block copolymers, whereby two crystallisable blocks are covalently tethered to one another, the molecular weight of the individual blocks and their relative weight fraction are important structural parameters that control their crystallisation. In the case of block copolymer micelles, these parameters can influence the crystallinity of the core, which has implications for drug encapsulation and release. Therefore, in this study, we aimed to determine how the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers contributes to the crystallinity of their hydrophobic PCL micelle cores. Using a library of PEG-b-PCL copolymers with PEG number-average molecular weight (Mn) values of 2, 5, and 10 kDa and weight fractions of PCL (fPCL) ranging from 0.11 to 0.67, the thermal behaviour and morphology were studied in blends, bulk, and micelles using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WXRD), and Synchrotron wide-angle X-ray scattering (WAXS). Compared to PEG and PCL homopolymers, the block copolymers displayed reduced crystallinity in the bulk phase and the individual blocks had a large influence on the crystallisation of one another. The fPCL was determined to be the dominant contributor to the extent and order of crystallisation of the two blocks. When fPCL < 0.35, the initial crystallisation of PEG led to an amorphous PCL phase. At fPCL values between 0.35 and 0.65, PEG crystallisation was followed by PCL crystallisation, whereas this behaviour was reversed when fPCL > 0.65. For lyophilised PEG-b-PCL micelles, the crystallinity of the core increased with increasing fPCL, although the core was predominately amorphous for micelles with fPCL < 0.35. These findings contribute to understanding the relationships between copolymer microstructure and micelle core crystallinity that are important for the design and performance of micellar drug delivery systems, and the broader application of polymer micelles.

A facile route to improve compatibilization of low density polyethylene/poly (ε-caprolactone) blends

Low density Polyethylene (designated hereafter as “PE”) is known for its inactivity, durability and resistance to degradation. For this reason adding pro-oxidants as additives in PE matrix could be efficient to elaborate a material designated as Ox-PE, exhibiting chemical reactivity. This modification could lead to an enhancement of compatibility between Ox-PE and other functionalized polymers. This approach has been exploited in this report to elaborate blends of Ox-PE with poly (ε-caprolactone) (PCL), a biodegradable polymer. Fourier Transform InfraRed spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and thermal characterization by DSC, TGA were applied to investigate structural and thermal properties of PE/PCL (75/25 wt%/wt%) blends, compatibilized with 1 Phr and 5 Phr of Ethylene-co-Glycidyl MethAcrylate (EGMA) copolymer or with a Ox-PE/PCL mixture.Structural observations of the PE75/PCL25 blend by SEM revealed a phase separated morphology indicating incompatibility between PE and PCL. This was also confirmed by FTIR spectroscopy where no changes were noticed concerning the characteristic bands of either PE or PCL. Incorporating EGMA in the PE75/PCL25 blend resulted in reduced particle sizes of the dispersed PCL phase in the PE matrix confirming the reaction of epoxy groups of EGMA with hydroxyl end-groups of PCL at the interface. Regarding the thermal behavior, all PE/PCL blends exhibited an intermediate response between that of PE and PCL homopolymers. Interestingly, a high degree of compatibility was achieved for the Ox-PE75/PCL25 blend, together with a lower thermal stability compared to PE75/PCL25.

Performance of Poly(caprolactone) (PCL) as an Impact Modifier for Polystyrene (PS): Effect of Functionalized Compatibilizers with Maleic Anhydride and Glycidyl Methacrylate

In this work, the copolymers ethylene-glycidyl methacrylate (E-GMA), ethylene methyl methacrylate-glycidyl methacrylate (EMA-GMA), and styrene-(ethylene-butylene)-styrene grafted with maleic anhydride (SEBS-g-MA) were used to compatibilize polystyrene (PS)/poly(caprolactone) (PCL) blends. The blends were processed in a co-rotating twin-screw extruder and injection molded. Samples were investigated by torque rheometry, capillary rheometry, impact strength, tensile strength, heat deflection temperature (HDT), dynamic-mechanical thermal analysis (DMTA), thermogravimetry (TG), and scanning electron microscopy (SEM). Torque rheometry indicated that glycidyl methacrylate functional groups and maleic anhydride groups interact with PCL. Capillary rheometry evidenced that at shear rates lower than 10,000 s−1, the PS/PCL/SEBS-g-MA blends presented the highest apparent viscosity among the blends. Such behavior was possibly due to the good interaction between SEBS-g-MA and the PS and PCL phases. Consequently, the properties of impact strength, elongation at break, tensile strength, and elastic modulus were improved by 30%, 109%, 33.8%, and 13.7%, respectively, compared with the non-compatibilized PS/PCL system. There was a reduction in the HDT of all blends compared with neat PS, given the elastomeric characteristics of PCL and compatibilizers. The DMTA results revealed two independent peaks in the blends (one around −53 °C concerning the PCL phase and another at 107 °C related to PS), confirming their immiscibility. The PS/PCL/SEBS-g-MA blends showed higher morphological stability, confirming their good mechanical properties.

Novel Silver-Functionalized Poly(ε-Caprolactone)/Biphasic Calcium Phosphate Scaffolds Designed to Counteract Post-Surgical Infections in Orthopedic Applications.

In this study, we designed and developed novel poly(ε-caprolactone) (PCL)-based biomaterials, for use as bone scaffolds, through modification with both biphasic calcium phosphate (BCP), to impart bioactive/bioresorbable properties, and with silver nitrate, to provide antibacterial protection against Staphylococcus aureus, a microorganism involved in prosthetic joint infections (PJIs). Field emission scanning electron microscopy (FESEM) showed that the samples were characterized by square-shaped macropores, and energy dispersive X-ray spectroscopy analysis confirmed the presence of PCL and BCP phases, while inductively coupled plasma–mass spectrometry (ICP–MS) established the release of Ag+ in the medium (~0.15–0.8 wt% of initial Ag content). Adhesion assays revealed a significant (p < 0.0001) reduction in both adherent and planktonic staphylococci on the Ag-functionalized biomaterials, and the presence of an inhibition halo confirmed Ag release from enriched samples. To assess the potential outcome in promoting bone integration, preliminary tests on sarcoma osteogenic-2 (Saos-2) cells indicated PCL and BCP/PCL biocompatibility, but a reduction in viability was observed for Ag-added biomaterials. Due to their combined biodegrading and antimicrobial properties, the silver-enriched BCP/PCL-based scaffolds showed good potential for engineering of bone tissue and for reducing PJIs as a microbial anti-adhesive tool used in the delivery of targeted antimicrobial molecules, even if the amount of silver needs to be tuned to improve osteointegration.

Morphology evolution to form double percolation polylactide/polycaprolactone/MWCNTs nanocomposites with ultralow percolation threshold and excellent EMI shielding

Morphological transformation only occurs in polymer blends via changing their components, which can be utilized to form double percolation structures. However, the weight percentage of either polymer in the blend generally ranges from 40 wt% to 60 wt%, which does not favor the construction of a densely conductive path. Herein, a double percolation structure had been successfully constructed in a polylactide-polycaprolactone (PLA/PCL) blend with only 30 wt% PCL by adding silicon dioxide (SiO2) to the PLA phase. The added SiO2 effectively strengthens the viscosity and elasticity of the PLA phase, which results in the morphological transformation of the PCL phase from segregated to continuous. In the blend, multi-wall carbon nanotubes (MWCNTs) were selectively distributed in the PCL phase to construct a more efficient conductive network, which brings about an enormous increase in conductivity for the nanocomposites. The electrical conductivity of PLA/PCL nanocomposite increases from 1.19 × 10−14 S/m to 4.57 × 10−4 S/m with the addition of 1.0 wt% MWCNTs and 6.0 wt% SiO2. The percolation threshold of the MWCNTs in the nanocomposite (0.11 wt%, i.e. 0.06 vol%) is 125% lower than that without SiO2 (0.28 wt%, i.e. 0.14 vol%). Furthermore, the nanocomposites with SiO2 were found to exhibit an electromagnetic interference (EMI) of approximately 26 dB with only 3.0 wt% MWCNTs, which means it can block 99.997% of microwaves. This study would provide a critical method to design eco-friendly nanocomposites with ultralow percolate threshold and excellent EMI shielding.

Effects of curing temperature on the structure and properties of epoxy resin-poly(ε-caprolactam) blends

Improving the toughness of epoxy resins (EP) with diverse thermoplastic polymers through curing reaction induced phase separation (RIPS) has been widely studied, with the prerequisite of designing and tailoring the phase morphology evolution of the blend. Herein, two typical amine-type curing agents, 4,4′-diamino diphenylmethane (DDM) with precuring temperature at around 150 °C and diethylenetriamine (DETA) at 80 °C were utilized to regulate and control the phase structures of EP-poly(ε-caprolactone) (PCL) blends. The curing temperature above or below the melting temperature (Tm) of PCL resulted in different states of PCL. The effect of curing temperature on the miscibility between EP matrix and PCL phase, and the correlation between phase morphology evolution and thermomechanical behavior, mechanical properties were comprehensively investigated for the first time. Results revealed that when the curing temperature of EPDDM-PCL blends was higher than the Tm of PCL, curing took place without phase separation; while distinct phase separation took place when EPDETA-PCL was cured at a temperature below the Tm of PCL. When the curing temperature was high, the PCL was able to dissolve completely in the resin before crosslinking began, so that semi-interpenetrating networks were formed; and that when the curing temperature was low, the PCL was unable to dissolve, and therefore formed separate particles. Consequently, the EPDDM-PCL blends exhibited all-leading mechanical properties due to the entanglement and slippage between PCL chains and EP networks. The strength of EPDETA-PCL was reduced but the toughness was improved for island-shaped PCL particles bridging or pinning the cracks during failure. These results elucidated the effect of the phase morphologies formed at different curing temperature on mechanical properties, and provided significant insights regarding the toughening of thermosets.

Understanding release kinetics and collapse proof suture retention response of curcumin loaded electrospun mats based on aliphatic polyesters and their blends

The paper aims at designing and fabrication of PLA/PCL blended suture resistant electrospun mats (EMs) encapsulating non-toxic curcumin and optimization of its release behavior, to facilitate its sustained release at the targeted areas, without complexation with any chemical and/or synthetic drug. The release of curcumin from PLA/PCL blended EMs followed a diffusion-controlled mechanism, as evident from the agreement of the experimental release data with Peppas- Korsmeyer, Higuchi, and Kopcha model. The curcumin embedded EMs have effectively rendered a release confirming to a new generalized logarithmic model. PLA/PCL blended EMs have proved to be an excellent carrier system, exhibiting enhanced cumulative curcumin release with an increase in curcumin loading. The evaluation of structural and viscoelastic properties of the fabricated EMs showed an increase in modulus and strength, along with a subsequent decrease in elongation, with an increase in curcumin content. Suture-induced cooperative collapse dynamics the EMs have been found to be a three-stage process involving stable, stable-unstable, and fast-unstable structural failure corresponding to network realignment, lateral pullout/fracture of fibers, and divergent tearing along the crack path. The viscoelastic responses showed a prominent shift in glass transition temperature (Tg) of the PCL phase indicating the development of curcumin-induced microstructural changes attributed to the H-bonding interaction with polymer segments of PLA/PCL-based EMs. Our study demonstrates, functionally efficient designing of PLA/PCL-based curcumin-loaded biodegradable EMs with sustained retention of tunable mechanical properties and hydrophobicity, irrespective of the extent of (in-vitro) curcumin release.

Preparation of super-toughened Poly(L-lactide) composites under elongational flow: A strategy for balancing stiffness and ductility

In this work, elongational flow supplied by a novel extrusion device, eccentric rotor extruder (ERE), was employed to prepare high-performance poly(L-lactide) (PLA)/poly(ε-caprolactone) (PCL) composites. Scanning electron microscopy (SEM) evidenced the elongational flow induced in-situ fiberization, in which the dispersed PCL were stretched into nanofibrils, consequently improved the interfacial adhesion of PLA/PCL. Differential scanning calorimetry (DSC), two-dimensional small-angle X-ray scattering (2D-SAXS), two-dimensional wide-angle X-ray diffraction (2D-WAXD) and dynamic mechanical analysis (DMA) were used to investigate the compatibility and crystallization of all composites. Consequently, we confirmed the enhanced compatibility and crystallinity were due to PLA's heterogeneous crystal nucleation on the nano-fibrillated PCL phases and the orientation of the PLA in a particular direction, which were considered induced by the elongational flow. Ultimately, we showed that the elongation at break of PLA with a low loading (20 wt%) of PCL is significantly improved to 476.7%, which is over 57 times that of the neat PLA. Meanwhile, the slight reduction in tensile strength is less than 20%. Enhanced thermal stability was also monitored due to the improved compatibility of PLA-PCL and the increased crystallinity of PLA.

Effect of Melt-Compounding Protocol on Self-Aggregation and Percolation in a Ternary Composite.

A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 × 10−2 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeter~aggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G′), high Young’s modulus, high dielectric loss (ε″), and negative–positive switching of dielectric constant at high frequency (of 103 Hz) of composite.

Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/styrene‐butadiene‐styrene)

AbstractThe shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross‐linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (Mw). The question here is: If the Mw of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ‐caprolactone) (PCL) and 60% styrene‐butadiene‐styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its Mw. It is shown that this change is only related to the variation in the Mw of PCL. After that, different samples with a distinct average Mw are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (Rr) for each of them is determined. It is found that when Mw of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in Mw. The tests show that the alteration in the blend's Mw influences its SME. Indeed, Rr of the (PCL/SBS) mixture drops with the decrease in Mw of PCL.

Highly toughened and heat resistant poly(l-lactide)/poly(ε-caprolactone) blends via engineering balance between kinetics and thermodynamics of phasic morphology with stereocomplex crystallite

Enhancing matrix crystallization via forming stereocomplex (SC) crystallite has been considered as an effect way to improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) when blending with other polymers. However, the roles of some of the key parameters, such as the kinetics of morphology evolution in blends, remain, yet, unclear, causing the troubles of the reproducibility of toughening PLLA by enhancing matrix crystallization and the stability in end-use applications (particularly in relative high temperature ranges). Herein, we provide a facile way to improve the toughness and heat resistance of PLLA via engineering the balance between the kinetics and thermodynamics of the dispersed phasic morphology in PLLA blends using PLLA/poly(ε-caprolactone) (PCL) (PLLA/PCL, 80/20 w/w) as an example, by adding a small amount of poly(d-lactide) (PDLA, ≤ 1% w/w). The few PDLA chains naturally interact with PLLA matrix chains, and co-crystallize to form SC crystallites, yielding high crystalline PPLA matrix but in controllable crystallization kinetics and increase of melting viscosity. As such, the coalescence or arrest of dispersed PCL phase is tailored via the tempo- and thermo-dimensional balance manipulation of thermal annealing (thermodynamics) and injecting moulding (quenching, dynamics), that relies on the PDLA content. The ease, with which highly impact toughened and heat-resistant PLLA materials were obtained by optimizing and matching the PDLA content and processing parameters including temperature and time, points to new directions in designing toughened PLLA with an economic manner.

Structure-properties correlations in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile)/nanosilica mixtures: Interrelationship among phase behavior, morphology and non-isothermal crystallization kinetics

In this work, the effects of amorphous poly(styrene-co-acrylonitrile) (SAN) chains and hydrophilic and hydrophobic nanosilica at different loadings on the non-isothermal crystallization kinetics of PCL phase have been evaluated using different theoretical models including Avrami, modified Avrami, Ozawa and Mo equations. Using microscopic observations, the interrelations among the changes in the kinetics parameters and the morphology and phase behavior of PCL/SAN and PCL/SAN/nanosilica mixtures have been thoroughly investigated. Microscopic observations on the nanocomposites showed differences in the nanofiller dispersion and distribution state as well as preferential migration and localization state. These differences lead to contradictory trends in the effects of hydrophilic and hydrophobic nanosilica on the crystallization kinetics of pure PCL and PCL/SAN blends. The nanoparticle migration during non-isothermal DSC tests in PCL/SAN blends, the formation of nanoparticle agglomerates at higher loadings, the restrictions imposed on the molecular movements in the crystallization growth stage and slower phase separation and dissolution of PCL/SAN/silica mixtures result in the cooling rate dependence of the kinetics parameters.

Design of electrical conductive poly(lactic acid)/carbon black composites by induced particle aggregation

AbstractThe electrical conductivity of ternary composites composed of a biopolymer blend with conductive particles (carbon black [CB]) is induced by the control of particle dispersion in the dispersed phase. If the CB particles have higher chemical affinity for the secondary phase (poly(caprolactone) [PCL]]) than the matrix (poly(lactic acid) [PLA]), especially as the concentration of the PCL phase decreases significantly to 4 wt%, the PCL phase induces the aggregation of CB particles beyond the selective localization, resulting in a shift of the particle percolation threshold to a lower concentration of particles (2.44 wt% CB). Moreover, the mixing ratio between the CB and the PCL phase significantly affects the formation of percolation of particles. When the mixing ratio of CB to PCL is equivalent (1:1), the ternary composite shows high electrical DC conductivity above 1 S/m with 10 wt% CB. The addition of a small amount of PCL induces the formation of particle aggregates with a high aspect ratio, providing more electron transfer pathways due to the multiple points of contact between the particle aggregates (power law scaling exponent of the composites ~2.14). Meanwhile, a binary composite (PLA/CB) never reaches high electrical conductivity of 1 S/m and even requires a greater concentration of CB (13 wt% CB for 10−3 S/m) to accomplish electron transfer because of the small aspect ratio of randomly dispersed particle aggregates (power law scaling exponent ~3.20).