Crystallization,mechanical properties,and enzymatic degradation of biodegradable poly(ε‐caprolactone) composites with poly(lactic acid) fibers

Biodegradable polymer composites based on poly(ɛ‐caprolactone) (PCL) and poly(lactic acid) (PLA) fibers were prepared by melt compounding. The effects of PLA fibers on the crystallization, mechanical properties, and enzymatic degradation of PCL composites were investigated. The addition of PLA fibers enhanced the crystallization of PCL due to the heterogeneous nucleation effect of fibers. However, the final crystallinity of the PCL in the composites was little changed in the presence of PLA fibers. With the addition of PLA fibers, significant improvement in storage modulus (E′) of PCL in the composites was achieved. A significant increase in E′ was 173% for the composites as compared to that of the neat PCL at 20°C. With the increase in PLA fibers content, the PCL composites showed decreased elongation and strength at break; however, the tensile yield strength and modulus were increased significantly, indicating that PCL was obviously reinforced by adding PLA fibers. Although the PLA fibers retarded the enzymatic degradation of PCL, it was possible to be completely degraded without much degradation time for PCL blending with suitable amounts of PLA fibers. POLYM. COMPOS., 34:1745–1752, 2013. © 2013 Society of Plastics Engineers     

Toward environment‐friendly composites of poly(ε‐caprolactone) reinforced with stereocomplex‐type poly(l‐lactide)/poly(d‐lactide)

In this work, stereocomplex‐poly(l ‐ and d ‐lactide) (sc‐PLA) was incorporated into poly(ε‐caprolactone) (PCL) to fabricate a novel biodegradable polymer composite. PCL/sc‐PLA composites were prepared by solution casting at sc‐PLA loadings of 5–30 wt %. Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) demonstrated the formation of the stereocomplex in the blends. DSC and WAXD curves also indicated that the addition of sc‐PLA did not alter the crystal structure of PCL. Rheology and mechanical properties of neat PCL and the PCL/sc‐PLA composites were investigated in detail. Rheological measurements indicated that the composites exhibited evident solid‐like response in the low frequency region as the sc‐PLA loadings reached up to 20 wt %. Moreover, the long‐range motion of PCL chains was highly restrained. Dynamic mechanical analysis showed that the storage modulus (E′) of PCL in the composites was improved and the glass transition temperature values were hardly changed after the addition of sc‐PLA. Tensile tests showed that the Young's modulus, and yield strength of the composites were enhanced by the addition of sc‐PLA while the tensile strength and elongation at break were reduced. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40208.     

Preparation and performance evaluation of tetracycline hydrochloride loaded wound dressing mats based on electrospun nanofibrous poly(lactic acid)/poly(ϵ‐caprolactone) blends

In this article, we present the drug‐release rate, water uptake, water permeability, morphology, and mechanical properties of a series of active wound dressing nanofibrous mats prepared via an electrospinning process of poly(lactic acid) (PLA), poly(?‐caprolactone) (PCL), and their (50/50) blends loaded with different doses of tetracycline hydrochloride antibiotic. The performance of these active wound dressings in terms of a sustained and suitable drug‐release rate, adequate water uptake and water permeability, and antibacterial activities were compared with those of a commercial wound dressing (Comfeel Plus). The results show that the dressings made from PCL and PLA/PCL blends showed better performance compared with the commercial wound dressing sample as far as these properties were concerned. The improved performance could be explained on the basis of the nanofibrous structure of the mats and the hydrophilicity of PCL and PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of poly(lactic acid)‐based polyurethanes

Poly(lactic acid) (PLA) is a biodegradable aliphatic polyester, but its brittleness makes it unsuitable for many packaging and appliance applications. The goal of the work reported was to create novel poly(ester urethane)s that incorporate biodegradable poly(lactic acid) diols (PLA‐OHs) and good mechanical properties of increased molecular weight via crosslinked network formation for engineering plastics applications. Three kinds of polyols (PLA‐OHs, PLA‐OHs/poly(tetramethylene ether) glycol or PLA‐OHs/poly(butylene adipate) glycol (PBA)) and two kinds of diisocyanates (4,4‐diphenylmethane diisocyanate (MDI) or toluene 2,4‐diisocyanate (TDI)) were chosen for the soft and hard segments to compare their mechanical properties. In addition, 1,4‐butanediol and trimethylolpropane were each used as chain extender agents. Results showed the PLA/PBA‐polyurethanes (PLA/PBA‐PUs) of the MDI series and the PLA/PBA‐PUs of the TDI series had improved thermal stability and enhanced mechanical properties. Degradation behavior showed the PLA‐based polyurethanes could be degraded in phosphate‐buffered saline solution and enzyme solution. © 2012 Society of Chemical Industry     

Synthesis and properties of novel biodegradable poly(ε‐caprolactone)/ poly(ethylene glycol)‐based polyurethane elastomers

Elastomeric polyurethanes with tunable biodegradation properties and suitable for numerous biomedical applications were synthesized via reaction of epoxy‐terminated polyurethanes (EUPs) with 1,6‐hexamethylenediamine as curing agent. The EUPs themselves were prepared from glycidol and isocyanate‐terminated polyurethanes made from poly(ε‐caprolactone) (PCL) or poly(ethylene glycol) (PEG) and 1,6‐hexamethylene diisocyanate. All the polymers were characterized by conventional methods, and their physical, mechanical, thermal, and degradation properties were studied. The results showed that the degradation rate and mechanical properties of the final products can be controlled by the amount of PEG or PCL present in the EUP. Increasing the PEG content causes an increase of hydrolytic degradation rate, and increasing the PCL content improves the mechanical properties of the final products. Evaluation of cytotoxcicity showed nontoxic behavior of the prepared samples, but the cytocompatibility of these polymers needs to be improved. Copyright © 2006 Society of Chemical Industry     

Rheology,mechanical properties,and biodegradation of poly(ε‐caprolactone)/silica nanocomposites

Biodegradable poly(ε‐caprolactone) (PCL)/silica nanocomposites containing 1–9 wt% silica nanoparticles were prepared by melt compounding in this work. The rheology, mechanical properties, and biodegradation were investigated. PCL/silica nanocomposite shows a high percolation threshold, which is between 7 and 9 wt%. Once percolation network structure forms, the long‐range motion of PCL chains is highly restrained. From the results of mechanical tests, the tensile strength, modulus, and yield strength of the nanocomposites are enhanced by the incorporation of silica nanoparticles. Moreover, it is interesting to find that the biodegradation rates have been enhanced obviously in the PCL/silica nanocomposites than in neat PCL, which may be of great use for the practical application of PCL. POLYM. COMPOS., 34:1620–1628, 2013. © 2013 Society of Plastics Engineers     

A comparative study of poly(l‐lactide)‐block‐poly(ϵ‐caprolactone) six‐armed star diblock copolymers and polylactide/poly(ϵ‐caprolactone) blends

This paper deals with the synthesis of a series of six‐armed star diblock copolymers based on poly(l ‐lactide) (PLLA) and poly(?‐caprolactone) (PCL) by ring‐opening polymerization using stannous octoate as catalyst and the preparation of polylactide (PLA)/PCL linear blends using a solution blending technique, while keeping the PLA‐to‐PCL ratio comparable in both systems. The thermal, rheological and mechanical properties of the copolymers and the blends were comparatively studied. The melting point and the degree of crystallinity were found to be lower for the copolymers than the blends due to poor folding property of star copolymers. Dynamic rheology revealed that the star polymers have lower elastic modulus, storage modulus and viscosity as compared to the corresponding blends with similar composition. The blends show two‐phase dispersed morphology whereas the copolymers exhibited microphase separated morphology with elongated (worm‐like) microdomains. The crystalline structures of the copolymers were characterized by larger crystallites than their blend counterparts, as estimated using Sherrer's equation based on wide‐angle X‐ray diffraction data. © 2016 Society of Chemical Industry     

Solid state NMR analysis of poly(L‐lactide) random copolymer with poly(ε‐caprolactone) and its reactive extrusion process

A random copolymer based on poly(L ‐lactide) (PLA) with poly(ε‐caprolactone) (PCL) was prepared and characterized by mechanical testing and solid state NMR, compared with a polymer blend. For a monofilament sample consisting of PLA/PCL random copolymer, there were negative correlations between the CL content and the mechanical properties: tensile strength, tensile elastic modulus, flexural rigidity, and flexural hysteresis decreased with increasing CL content. In contrast, the mechanical properties of the polymer blend were only slightly changed by addition of the CL unit. For the random copolymer, the addition of a small amount of CL reduced relaxation times, T₁C and T_1ρH, gradually. The T₁C and T_1ρH values correlated closely with the tensile elastic modulus and the tensile strength, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermorheological properties of poly (ε‐caprolactone)/polylactide blends

Blends of poly (ε‐caprolactone) (PCL)/polylactide (PLA) were prepared by solution‐casting method to study their thermal and rheological properties. Differential scanning calorimetry thermographs have shown two separate melting peaks in the blends, which are indicative of immiscible structure at all compositions. Scanning electron microscopy images show droplet morphology of PCL into PLA matrix up to 40 wt% of PCL. Above this concentration, the co‐continuous morphology starts to appear, which becomes again droplet morphology for blends with concentration of PCL higher than about 60 wt%. The viscoelastic properties of the various blends were investigated using rotational rheometry. The enhancement of the elastic modulus of blends at small frequencies at which terminal zone behavior is expected, is a signature behavior of immiscible systems due to the presence of interface and contribution to the stress from interfacial tension. Two emulsion models were used to predict the viscoelastic properties of the blends from the corresponding properties of their pure components that led to the determination of the interfacial tension of PCL/PLA in agreement with experimental findings. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Reactive compatibilization of biodegradable poly(lactic acid)/poly(ε‐caprolactone) blends with reactive processing agents

Poly(lactic acid) (PLA) blended with poly(ε‐caprolactone) (PCL) was prepared with various reactive processing agents. Four isocyanates‐lysine triisocyanate (LTI); lysine diisocyanate (LDI); 1,3,5‐tris(6‐isocyanatohexyl)‐1,3,5‐triazinane‐2,4,6‐trione (Duranate TPA‐100); 1,3,5‐tris(6‐isocyanatohexyl)biuret (Duranate 24A‐100)‐and an industrial epoxide‐trimethylolpropane triglycidyl ether (Epiclon 725)‐were used as reactive processing agents. PLA/PCL blended in the presence of LTI had the highest torque in a mixer test. The test specimens were prepared by injection molding. The mechanical properties, thermal properties, molecular weight, melt viscosity, phase behavior, and morphology were investigated using tensile strength, impact strength, differential scanning calorimetry, melt mass‐flow rate measurements, capillary rheometery, gel permeation chromatography, laser scanning confocal microscopy (LSCM), and visco‐elasticity atomic force microscopy (VE‐AFM). The impact strength increased considerably at 20 wt% PCL. The nominal tensile strain of PLA/PCL blended with LTI increased by 270%. The MFR values of PLA/PCL blends decreased with increasing LTI. Similar results were observed for shear viscosity. LSCM measurements showed that the diameters of PCL were dispersed about 0.4 μm in the presence of LTI. VE‐AFM showed that spherical particles with diameters of 50 nm were PCL‐rich domain. These results indicate that isocyanate groups of LTI react with both terminal hydroxyl or carboxyl groups of polymers, and the compatibility of PLA/PCL blends improves with LTI by reactive processing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Influence of lactic acid on degradation and biocompatibility of electrospun poly(ε‐caprolactone) fibers

Electrospinning of a poly(ε‐caprolactone) (PCL)/lactic acid (LA) blend was investigated to fabricate electrospun PCL fibers with improved biodegradability and biocompatibility for biomedical applications. Simple blending of PCL solution with various amounts of LA was used for electrospinning, and the physicochemical properties of the as‐fabricated mat were evaluated using various techniques. Scanning electron microscopy showed that fiber diameter decreased with increasing amount of LA. Fourier transform infrared spectroscopy and thermogravimetric analysis also revealed that LA was successfully incorporated in PCL fibers. The presence of LA can accelerate the biodegradation of PCL fibers and enhance the hydrophilicity of a membrane. The adhesion, viability and proliferation properties of osteoblast cells on the PCL/LA composite fibers were analyzed using in vitro cell compatibility tests which showed that LA can increase the cell compatibility of PCL fibers. Additionally, subsequent conversion of LA into calcium lactate by neutralization with calcium base can provide Ca²⁺ ions on the fiber surface to promote the nucleation of CaPO₄ particles. © 2013 Society of Chemical Industry     

Effect of electrospun fibers of polyhydroxybutyrate filled with different organoclays on morphology,biodegradation, and thermal stability of poly(ε‐caprolattone)

The properties of nanocomposites of poly(ε‐caprolattone) (PCL) were studied, the pristine PCL was implemented with the introduction of electrospun fibers of polyhydroxybutyrate (PHB), containing a cationic (Cloisite) or an anionic (Perkalite) clay. These multicomponent composites containing a very low amount of clay confined in fibers are different from usual nanocomposite materials containing clay dispersed in the polymer matrix, which are produced by solvent casting or melt extrusion. To analyze the influence of the different fillers on the final composite, a preliminary study on PHB cast films and fibers prepared from the same solution was carried out, and then a thorough analysis was accomplished of the behavior of these particular nanocomposites PCL/PHB fibers/clay to elucidate the effects of the filled electrospun fibers on the PCL matrix. The structure and morphology of the samples were characterized by wide‐angle X‐ray diffraction and small angle X‐ray scattering; differential scanning calorimetry and thermogravimetric analysis were used to understand the influence of the fillers on the thermal behavior and stability; mechanical properties were evaluated and biodegradation studies were carried out. The PHB electrospun fibers and the fractured surface of the final composites were examined by scanning electron microscopy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42342.     

Morphological characteristics and thermal,rheological, and mechanical properties of cellulose nanocrystals-containing biodegradable poly(lactic acid)/poly(ε-caprolactone) blend composites

This work investigates the effect of cellulose nanocrystal (CN) loading on the properties of polylactide / poly(ε-caprolactone) (PLA/PCL) (70/30) blend processed in a twin-screw extruder as a potential material that can be utilized in various applications where biodegradation is highly desired. The morphological analysis revealed a reduction in droplet size of dispersed PCL phase upon addition of CN at low concentrations (1 and 2 wt %) with maximum reduction at 2 wt % which led to maximum improvement in mechanical properties. The reinforcing effect of CN in increasing the DMA storage modulus of the prepared systems was noticed when CN concentration was increased. Further, CN enhanced the crystallization of PCL, whereas the cold crystallization of PLA remained the same with CN addition. Both melt strength and viscosity of PLA improved with the incorporation of PCL and CN. In general, a green composite material with improved properties was successfully prepared using an environmentally friendly filler material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48665.     

Crystallization,morphology, and mechanical behavior of polylactide/poly(ε‐caprolactone) blends

Optically pure polylactides, poly(L ‐lactide) (PLLA) and poly(D ‐lactide) (PDLA), were blended across the range of compositions with poly(ε‐caprolactone) (PCL) to study their crystallization, morphology, and mechanical behavior. Differential scanning calorimetry and dynamic mechanical analysis (DMA) of the PLA/PCL blends showed two T_gs at positions close to the pure components revealing phase separation. However, a shift in the tan δ peak position by DMA from 64 to 57°C suggests a partial solubility of PCL in the PLA‐rich phase. Scanning electron microscopy reveals phase separation and a transition in the phase morphology from spherical to interconnected domains as the equimolar blend approaches from the outermost compositions. The spherulitic growth of both PLA and PCL in the blends was followed by polarized optical microscopy at 140 and 37°C. From tensile tests at speed of 50 mm/min Young's modulus values between 5.2 and 0.4 GPa, strength values between 56 and 12 MPa, and strain at break values between 1 and 400% were obtained varying the blend composition. The viscoelastic properties (E′ and tan δ) obtained at frequency of 1 Hz by DMA are discussed and are found consistent with composition, phase separation, and crystallization behavior of the blends. POLYM. ENG. SCI., 46:1299–1308, 2006. © 2006 Society of Plastics Engineers     

Miscibility of block copolymers of poly(ε‐caprolactone) and poly(ethylene glycol) with poly(3‐hydroxybutyrate) as well as the compatibilizing effect of these copolymers in blends of poly(ε‐caprolactone) and poly(3‐hydroxybutyrate)

Atactic poly(3‐hydroxybutyrate) (a‐PHB) and block copolymers of poly(ethylene glycol) (PEG) with poly(ε‐caprolactone) (PCL‐b‐PEG) were synthesized through anionic polymerization and coordination polymerization, respectively. As demonstrated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) measurements, both chemosynthesized a‐PHB and biosynthesized isotactic PHB (i‐PHB) are miscible with the PEG segment phase of PCL‐b‐PEGs. However, there is no evidence showing miscibility between both PHBs and the PCL segment phase of the copolymer even though PCL has been block‐copolymerized with PEG. Based on these results, PCL‐b‐PEG was added, as a compatibilizer, to both the PCL/a‐PHB blends and the PCL i‐PHB blends. The blend films were obtained through the evaporation of chloroform solutions of mixed components. Excitingly, the improvement in mechanical properties of PCL/PHB blends was achieved as anticipated initially upon the addition of PCL‐b‐PEG. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2600–2608, 2001     

Preparation,characterization, and mechanical properties of poly(ε‐caprolactone)/polylactic acid blend composites

Mechanical properties of poly(ε‐caprolactone) (PCL) and polylactic acid (PLA) blend reinforced with Dura and Tenera palm press fibers were studied. Dicumyl peroxide (DCP) was used as compatibilizer in the blend composites. Fourier transforms infrared spectrophotometer (FTIR) and field emission scanning electron microscope (FESEM) was used to study the effect of treatment on the fibers and fiber/matrix adhesion respectively. The uncompatibilized blend composites exhibited higher Young's modulus than the compatibilized blend composites. Impact strength of compatibilized blend composites of Tenera fibers (FM) increased by 161% at 10 wt% fiber load more than the uncompatibilized blend composites at same fiber load. The Dura fibers (FN) enhanced impact strength by 133% at 10 wt% fiber load. Tensile strength increased by 40% for compatibilized FM blend composites. In conclusion, it was observed that DCP incorporation resulted in good interfacial adhesion as revealed by the FESEM micrographs and evidenced in the improved mechanical properties. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Mechanical properties of poly(ε‐caprolactone) and poly(lactic acid) blends

The aim of this work was to better understand the performance of binary blends of biodegradable aliphatic polyesters to overcome some limitations of the pure polymers (e.g., brittleness, low stiffness, and low toughness). Binary blends of poly(ε‐caprolactone) (PCL) and poly(lactic acid) (PLA) were prepared by melt blending (in a twin‐screw extruder) followed by injection molding. The compositions ranged from pure biodegradable polymers to 25 wt % increments. Morphological characterization was performed with scanning electron microscopy and differential scanning calorimetry. The initial modulus, stress and strain at yield, strain at break, and impact toughness of the biodegradable polymer blends were investigated. The properties were described by models assuming different interfacial behaviors (e.g., good adhesion and no adhesion between the dissimilar materials). The results indicated that PCL behaved as a polymeric plasticizer to PLA and improved the flexibility and ductility of the blends, giving the blends higher impact toughness. The strain at break was effectively improved by the addition of PCL to PLA, and this was followed by a decrease in the stress at break. The two biodegradable polymers were proved to be immiscible but nevertheless showed some degree of adhesion between the two phases. This was also quantified by the mechanical property prediction models, which, in conjunction with material property characterization, allowed unambiguous detection of the interfacial behavior of the polymer blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of fiber structure on the properties of the electrospun hybrid membranes composed of poly(ε‐caprolactone) and gelatin

To elucidate the effect of fiber structure on the properties of the electrospun gelatin/PCL hybrid membranes, three types of fibers with different structures, i.e., core‐shell, blend, and mixed fibers were fabricated. The crystallinity, wettability, swelling degree, and mechanical properties of the hybrid membranes were compared. It was found that the crystalline characteristics of PCL in the core‐shell fibers were different from the fibers fabricated by the other two methods. That is, the orientation degree of the PCL chains in the core‐shell fibers was higher than that in both blend and mixed fibers. The wettability of the hybrid membrane was dependent on both the composition and structure of the electrospun fibers. Blended fibers exhibited the highest hydrophobicity because of the enrichment of PCL at the fiber surface. Contrarily, the mixed fibers possessed the highest mechanical strength of 3–5.18 MPa. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poly(butylene terephthalate)/poly(ε‐caprolactone) blends: Miscibility and thermal and mechanical properties

Miscibility and thermal and mechanical properties of poly(butylene terephthalate) (PBT) blends with poly(ε‐caprolactone) (PCL) were analyzed as a function of the molecular mass of PCL. It was found that the components are miscible when oligomeric PCL is blended with PBT, probably due to favorable interactions between ? OH end groups of poly(ε‐caprolactone) and ester groups of PBT. In the blends containing high molar mass PCL, the concentration of hydroxyl end groups is lower, allowing only partial miscibility of the components. The resulting materials display good mechanical properties, with enhanced performance at rupture compared to plain PBT. POLYM. ENG. SCI., 47:323–329, 2007. © 2007 Society of Plastics Engineers.     

Process study,development and degradation behavior of different size scale electrospun poly(caprolactone) and poly(lactic acid) fibers

This study describes the preparation of electrospun poly(caprolactone) (PCL) and poly(lactic acid) (PLA) fibrous scaffolds with and without nano-hydroxyapatite (nHAp) having nanoscale, microscale and combined micro/nano (multiscale) architecture. Processing parameters such as polymer concentration, voltage, flow rate and solvent compositions were varied in wide range to display the effect of each one in determining the diameter and morphology of fibers. The effect of each regulating parameter on fiber morphology and diameter was evaluated and characterized using scanning electron microscope (SEM). Degradability of the selected fibrous scaffolds was verified by phosphate buffered saline immersion and its morphology was analyzed through SEM, after 5 and 12 months. Quantitative measurement in degradation was further evaluated through pH analysis of the medium. Both studies revealed that PLA had faster degradation compared to PCL irrespective of the size scale nature of fibers. Structural stability evaluation of the degraded fibers in comparison with pristine fibers by thermogravimetric analysis further confirmed faster degradability of PLA compared to PCL fibers. The results indicate that PLA showed faster degradation than PCL irrespective of the size-scale nature of fibrous scaffolds, and therefore, could be applied in a variety of biomedical applications including tissue engineering.