Bio‐composites for structural applications: Poly‐l‐lactide reinforced with long sisal fiber bundles

Fully bio‐based and biodegradable composites were compression molded from unidirectionally aligned sisal fiber bundles and a polylactide polymer matrix (PLLA). Caustic soda treatment was employed to modify the strength of sisal fibers and to improve fiber to matrix adhesion. Mechanical properties of PLLA/sisal fiber composites improved with caustic soda treatment: the mean flexural strength and modulus increased from 279 MPa and 19.4 GPa respectively to 286 MPa and 22 GPa at a fiber volume fraction of V_f = 0.6. The glass transition temperature decreased with increasing fiber content in composites reinforced with untreated sisal fibers due to interfacial friction. The damping at the caustic soda‐treated fibers‐PLLA interface was reduced due to the presence of transcrystalline morphology at the fiber to matrix interface. It was demonstrated that high strength, high modulus sisal‐PLLA composites can be produced with effective stress transfer at well‐bonded fiber to matrix interfaces. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40999.     

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     

Influence of fly ash cenospheres on performance of coir fiber‐reinforced recycled high‐density polyethylene biocomposites

Recycled high‐density polyethylene (RHDPE)/coir fiber (CF)‐reinforced biocomposites were fabricated using melt blending technique in a twin‐screw extruder and the test specimens were prepared in an automatic injection molding machine. Variation in mechanical properties, crystallization behavior, water absorption, and thermal stability with the addition of fly ash cenospheres (FACS) in RHDPE/CF composites were investigated. It was observed that the tensile modulus, flexural strength, flexural modulus, and hardness properties of RHDPE increase with an increase in fiber loading from 10 to 30 wt %. Composites prepared using 30 wt % CF and 1 wt % MA‐g‐HDPE exhibited optimum mechanical performance with an increase in tensile modulus to 217%, flexural strength to 30%, flexural modulus to 97%, and hardness to 27% when compared with the RHDPE matrix. Addition of FACS results in a significant increase in the flexural modulus and hardness of the RHDPE/CF composites. Dynamic mechanical analysis tests of the RHDPE/CF/FACS biocomposites in presence of MA‐g‐HDPE revealed an increase in storage (E′) and loss (E″) modulus with reduction in damping factor (tan δ), confirming a strong influence between the fiber/FACS and MA‐g‐HDPE in the RHDPE matrix. Differential scanning calorimetry, thermogravimetric analysis thermograms also showed improved thermal properties in the composites when compared with RHDPE matrix. The main motivation of this study was to prepare a value added and low‐cost composite material with optimum properties from consumer and industrial wastes as matrix and filler. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42237.     

Carbon fiber‐reinforced gelatin composites. I. Preparation and mechanical properties

Composites were made from carbon fibers and gelatin using a solvent‐casting or solution‐impregnation technique. Relationships between the fiber volume fraction (Vf), glycerol (plasticizer) content, gelatin content, fiber form, and mechanical properties (tensile strength and modulus, elongation at break, and shear strength) of the composites were investigated. In long carbon fiber gelatin composite (C_L/Gel), tensile strength, modulus, and shear strength increased steadily with the Vf. In the case of a short carbon fiber gelatin composite (C_S/Gel), an initial improvement in tensile strength and modulus was followed by a reduction, whereas the shear strength improved with the Vf and then reached a constant value. The elongation decreased with the Vf for both composites. It is shown that C_L/Gel had higher values of strength, modulus, and elongation than did C_S/Gel at any Vf level. The effects of glycerol and gelatin contents on the mechanical properties of the composites were found to be much less significant as compared to the Vf. According to scanning electron microscopic observation of the fracture surfaces, the fibers were uniformly distributed in the gelatin matrix, but the interfacial adhesion between the gelatin matrix and the carbon fibers was not very good for both composites. Fiber surface modification would be necessary to further improve the mechanical properties of the two composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 987–993, 2000     

Fabrication and Physical Properties of Poly(ε‐Caprolactone)/Modified Graphene Nanocomposite

A chemical strategy is attempted to modify graphene for its facilitated dispersion in poly(ε‐caprolactone) (PCL) matrix. Herein, graphite oxide is subjected to sequential treatment with phenyl isocyanate and vitamin C (VC) to yield graphene nanosheets (iG‐VC). It is noteworthy that following the reduction treatment, iG‐VC graphene sheets exfoliate within the PCL matrix and show appreciable interfacial compatibility with PCL matrix in organic solvent by virtue of improved polarity from isocyanate treatment. The tensile yield strength and Young's modulus of the PCL/iG‐VC composite exhibit pronounced enhancement as compared to neat PCL, despite of mere composition of graphene sheets. The tensile yield stress of composite is increased notably to reach 18.6 MPa at 3 wt% graphene sheets as compared to neat PCL. Likewise, Young's modulus of composite is observed to increase from 370 to 470 MPa at 5 wt% graphene sheets. Moreover, the crystallization temperature (T _c) and crystallinity of PCL increase significantly upon incorporation of small amount of iG‐VC. Ultimately, functional role of iG‐VC graphene sheets is demonstrated in enhancing electrical conductivity of PCL‐based nanocomposites. The plausible mechanisms are also proposed to explain the increased T _c, improved mechanical property, and improved electrical conductivity of PCL/iG‐VC composite.

     

Reactive compatibilization and performance evaluation of miscanthus biofiber reinforced poly(hydroxybutyrate‐co‐hydroxyvalerate) biocomposites

Dicumyl peroxide (DCP) initiated reactive compatibilization of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV)/miscanthus fibers (70/30 wt %) based biocomposite was prepared in a twin screw extruder followed by injection molding. In the presence of DCP, both the flexural and the tensile strength of the PHBV/miscanthus composites were appreciably higher compared with PHBV/miscanthus composite without DCP as well as neat PHBV. The maximum tensile strength (29 MPa) and flexural strength (51 MPa) were observed in the PHBV/miscanthus composite with 0.7 phr DCP. The enhanced flexural and tensile strength of the PHBV/miscanthus/DCP composites are attributed to the improved interfacial adhesion by free radical initiator. Unlike flexural and tensile strength, the modulus of the PHBV/miscanthus/DCP composites was found to slightly lower than the PHBV/miscanthus composite. The modulus difference in the PHBV/miscanthus composite with and without DCP has good agreement with the observed crystallinity. However, the flexural and tensile modulus of all the prepared biocomposites was at least two fold higher than the neat PHBV. The storage modulus value of the PHBV/miscanthus and PHBV/miscanthus/DCP biocomposites follows similar trend like tensile and flexural modulus. The melting temperature and crystallization temperature of PHBV/DCP and PHBV/miscanthus/DCP samples were considerably lower compared with the neat PHBV and PHBV/miscanthus composites. The surface morphology revealed that the PHBV/miscanthus/DCP composites have good interface with less fiber pull‐outs compared with the corresponding counterpart without DCP. This suggests that the compatibility between the matrix and the fibers is enhanced after the addition of peroxide initiator. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44860.     

Hybrid effect on mechanical properties of M40‐T300 carbon fiber reinforced Bisphenol A Dicyanate ester composites

Interply and intraply hybrid composites based on Bisphenol A Dicyanate ester (BADCy), high strength carbon fibers T300, and high modulus carbon fibers M40 were prepared by monofilament dip‐winding and press molding technique. The tensile, flexural, interlaminar shear properties and SEM analysis of the hybrid composites with different fiber content and fiber arrangement were investigated. The results indicated that the mechanical properties of intraply hybrid composites were mainly determined by fiber volume contents. When the ratio of fiber volume content was close to 1:1, the intraply hybrid composites possessed lowest tensile and flexural strength. The mechanical properties of interply hybrid composite mainly depended on the fiber arrangement, instead of the fiber volume contents. The hybrid composites using T300 fiber layout as outside layer possessed high flexural strength and low flexural modulus, which was close to that of T300/BADCy composites. The hybrid composites ([(M40)_x/(T300)_y]_S) using M40 fiber layout as outside layer and T300 fibers in the mid‐plane had high flexural modulus and interlaminar shear strength. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Morphological and physicomechanical analysis of high‐density polyethylene filled with Salago fiber

The environmental issues associated with the mass discarding of waste plastics in the Philippines have significantly raised for the past decade. However, this country is a home to many natural fibers which necessitates the development of ecofriendly materials to diminish the environmental footprint of polymers. High‐density polyethylene (HDPE) was filled with floured untreated and 5 wt % alkaline‐treated Salago fiber via melt compounding. The physical and mechanical characteristics of both types of composites were measured and compared. The composite filled with 30 wt % untreated fiber became very brittle, showing tensile strength and impact resistance of 15.8 MPa and 4.9 kJ/m², respectively. Alkaline treatment improved the mechanical properties of untreated composites, but not above the value of virgin HDPE. Nevertheless, the flexural strength of treated composites exceeded that of the virgin HDPE. Untreated composites absorbed water twice as the treated ones. Finally, morphological and fractography inspection on tensile and flexural test specimens showed improvement made by treatment on the interfacial adhesion between fiber and thermoplastic, corroborating the results from mechanical properties test. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46479.     

Mechanical,thermal, and morphological properties of maleic anhydride‐g‐polypropylene compatibilized and chemically modified banana‐fiber‐reinforced polypropylene composites

Composites were prepared with chemically modified banana fibers in polypropylene (PP). The effects of 40‐mm fiber loading and resin modification on the physical, mechanical, thermal, and morphological properties of the composites were evaluated with scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Infrared (IR) spectroscopy, and so on. Maleic anhydride grafted polypropylene (MA‐g‐PP) compatibilizer was used to improve the fiber‐matrix adhesion. SEM studies carried out on fractured specimens indicated poor dispersion in the unmodified fiber composites and improved adhesion and uniform dispersion in the treated composites. A fiber loading of 15 vol % in the treated composites was optimum, with maximum mechanical properties and thermal stability evident. The composite with 5% MA‐g‐PP concentration at a 15% fiber volume showed an 80% increase in impact strength, a 48% increase in flexural strength, a 125% increase in flexural modulus, a 33% increase in tensile strength, and an 82% increase in tensile modulus, whereas the heat deflection temperature increased by 18°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties of modified biofiller‐polypropylene composites

This article reports the mechanical, thermal, and morphological properties of polypropylene (PP)‐chicken eggshell (ES) composites. Mechanical properties like tensile strength, tensile modulus, izod impact strength, flexural modulus of PP composites with normal (unmodified) eggshell and chemically treated ES [modified ES (MES) with isophthalic acid] have been investigated. PP–calcium carbonate (CaCO₃) composites, at the same filler loadings, were also prepared and used as reference. The results showed that PP composites with chemically MES had better mechanical properties compared to the unmodified ES and CaCO₃ composites. An increase of about 3–18% in tensile modulus, 4–44% in izod impact strength and 1.5–26% in flexural modulus at different filler loading was observed in MES composites as compared to unmodified ES composites. Scanning electron microscopy (SEM) micrographs of fractured tensile specimens confirmed better interfacial adhesion of MES with polymer matrix resulting into lower voids and plastic deformation resulting in improved mechanicals of the composites. TEM micrographs showed acicular needle shaped morphology for modified ES and have contributed to better dispersion which is the prime reason for enhancement of all the mechanical properties. At higher filler loading, the modulus of MES composite was found to be higher by 5% as compared to commercial CaCO₃ composites. POLYM. COMPOS., 35:708–714, 2014. © 2013 Society of Plastics Engineers     

A study of the mechanical properties of randomly oriented short banana and sisal hybrid fiber reinforced polyester composites

The mechanical performance of short randomly oriented banana and sisal hybrid fiber reinforced polyester composites was investigated with reference to the relative volume fraction of the two fibers at a constant total fiber loading of 0.40 volume fraction (V_f), keeping banana as the skin material and sisal as the core material. A positive hybrid effect is observed in the flexural strength and flexural modulus of the hybrid composites. The tensile strength of the composites showed a positive hybrid effect when the relative volume fraction of the two fibers was varied, and maximum tensile strength was found to be in the hybrid composite having a ratio of banana and sisal 4 : 1. The impact strength of the composites was increased with increasing volume fraction of sisal. However, a negative hybrid effect is observed when the impact strength of the composites is considered. Keeping the relative volume fraction of the two fibers constant, that is, banana : sisal = 0.32 : 0.08 (i.e., 4 : 1), the fiber loading was optimized and different layering patterns were investigated. The impact strength of the composites was increased with fiber loading. Tensile and flexural properties were found to be better at 0.40 V_f. In the case of different layering patterns, the highest flexural strength was observed for the bilayer composites. Compared to other composites, the tensile properties were slightly higher for the composite having banana as the skin material and sisal as the core material. Scanning electron micrographs of the tensile and impact fracture surfaces of the hybrid composites having volume fraction 0.20 and 0.40 V_f were studied. The experimental tensile strength and tensile modulus of hybrid composites were compared with those of theoretical predictions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1699–1709, 2005     

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 (M_n), 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     

Mechanical properties of teak wood flour‐reinforced HDPE composites

Mechanical properties such as tensile and impact strength behavior of teak wood flour (TWF)‐filled high‐density polyethylene (HDPE) composites were evaluated at 0–0.32 volume fraction (Φ_f) of TWF. Tensile modulus and strength initially increased up to Φ_f = 0.09, whereas a decrease is observed with further increase in the Φ_f. Elongation‐at‐break and Izod impact strength decreased significantly with increase in the Φ_f. The crystallinity of HDPE also decreased with increase in the TWF concentration. The initial increase in the tensile modulus and strength was attributed to the mechanical restraint, whereas decrease in the tensile properties at Φ_f > 0.09 was due to the predominant effect of decrease in the crystallinity of HDPE. The mechanical restraint decreased the elongation and Izod impact strength. In the presence of coupling agent, maleic anhydride‐grafted HDPE (HDPE‐g‐MAH), the tensile modulus and strength enhanced significantly because of enhanced interphase adhesion. However, the elongation and Izod impact strength decreased because of enhanced mechanical restraint on account of increased phase interactions. Scanning electron microscopy showed a degree of better dispersion of TWF particles because of enhanced phase adhesion in the presence of HDPE‐g‐MAH. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Compatibilizing effect of starch‐grafted‐poly(L‐lactide) on the poly(ε‐caprolactone)/starch composites

The poly(ε‐caprolactone) (PCL)/starch blends were prepared with a coextruder by using the starch grafted PLLA copolymer (St‐g‐PLLA) as compatibilizers. The thermal, mechanical, thermo‐mechanical, and morphological characterizations were performed to show the better performance of these blends compared with the virgin PCL/starch blend without the compatibilizer. Interfacial adhesion between PCL matrix and starch dispersion phases dominated by the compatibilizing effects of the St‐g‐PLLA copolymers was significantly improved. Mechanical and other physical properties were correlated with the compatibilizing effect of the St‐g‐PLLA copolymer. With the addition of starch acted as rigid filler, the Young's modulus of the PCL/starch blends with or without compatibilizer all increased, and the strength and elongation were decreased compared with pure PCL. Whereas when St‐g‐PLLA added into the blend, starch and PCL, the properties of the blends were improved markedly. The 50/50 composite of PCL/starch compatibilized by 10% St‐g‐PLLA gave a tensile strength of 16.6 MPa and Young's modulus of 996 MPa, respectively, vs. 8.0 MPa and 597 MPa, respectively, for the simple 50/50 blend of PCL/starch. At the same time, the storage modulus of compatibilized blends improved to 2940 MPa. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of polycaprolactone/polyglycolide blended electrospun fibers on the morphology and mechanical properties of polycaprolactone

Polycaprolactone (PCL) and polyglycolide (PGA) are two biopolymers that have been used as in situ biomedical devices for various applications. The obstacle of creating a composite that captures the benefit of PCL's long degradation time, while acquiring the strength from PGA is overcoming the lack of surface adhesion between the two biopolymers for stress transfer to occur. This study investigates the use of miscible PCL‐PGA blended fibers, created by electrospinning, to increase the interfacial bonding of fibers to the PCL matrix of the polymer–polymer composite. The use of the blended fibers will thereby create the ability of load transfer from the long‐term PCL matrix to the stronger PCL‐PGA fiber reinforcement. The incorporation of the PCL‐PGA fibers was able to increase the tensile yield strength and Young's modulus over that of the bulk PCL, while decreasing the percent elongation at break. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40224.     

Fabrication and properties of Cf/ZrC‐SiC‐based composites by an improved reactive melt infiltration

C_f/ZrC‐SiC composites with a density of 2.52 g/cm³ and a porosity of 1.68% were fabricated via reactive melt infiltration (RMI) of Si into nano‐porous C_f/ZrC‐C preforms. The nano‐porous C_f/ZrC‐C preforms were prepared through a colloid process, with a ZrC “protective coating” formed surrounding the carbon fibers. Consequently, highly dense C_f/ZrC‐SiC composites without evident fiber/interphase degradation were obtained. Moreover, abundant needle‐shaped ZrSi₂ grains were formed in the composites. Benefiting from this unique microstructure, flexural strength, and elastic modulus of the composites are as high as 380 MPa and 61 GPa, respectively, which are much higher than C_f/ZrC‐SiC composites prepared by conventional RMI.     

Micromechanics for fiber volume percent with a photocure vinyl ester composite

Micromechanics for fiber volume percent (V_f) from 0.0V_f to 54.0 V_f were conducted using (3 mm long × 9 μm diameter) high‐purity quartz fibers in a visible‐light vinyl ester particulate‐filled photocure resin. MTS fully articulated four‐point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm³ sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM‐C‐1161–94 and polymers ASTM‐D‐6272–00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule‐of‐mixtures theory as a valid representation of micromechanical physics. The rule‐of‐mixtures micromechanics described by V_f could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3V_f for modulus, 5.4V_f for flexural strength, and 10.3V_f for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in V_f correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four‐point bending test, p < 10⁻¹⁰. All mechanical properties in turn correlated highly significantly with one another, p < 10⁻⁹. POLYM. COMPOS., 28:294–310, 2007. © 2007 Society of Plastics Engineers     

Mechanical properties of talc‐ and (calcium carbonate)‐filled poly(vinyl chloride) hybrid composites

The main objective of this study was to investigate and compare the mechanical properties of poly(vinyl chloride) (PVC) composites filled with calcium carbonate (CaCO₃), talc, and talc/CaCO₃. Talc and CaCO₃ with different grades were incorporated into the PVC matrix. To produce the composites, the PVC resin, fillers, and other additives were first dry‐blended by using a laboratory mixer before being milled into sheets in a two‐roll mill. Test specimens were prepared by compression molding, after which the mechanical properties of the composites were determined. Single and hybrid filler loadings used were fixed at 30 phr (parts per hundred parts of resin). Talc‐filled composite showed the highest flexural modulus and the lowest impact strength, whereas uncoated, ground, 1‐μm CaCO₃ (SM 90) showed optimum properties in terms of impact strength and flexural modulus among all grades of CaCO₃. It was selected to combine with talc at different ratios in the hybrid composites. The impact strength of the hybrid composites gradually increased with increasing SM 90 content, but the flexural and tensile properties showed an opposite behavior. Hybrid (10 phr talc):(20 phr SM 90)‐filled PVC composite reached a synergistic hybridization with balanced properties in impact strength, as well as flexural and tensile properties. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Surface treatment of phosphate glass fibers using 2‐hydroxyethyl methacrylate: Fabrication of poly(caprolactone)‐based composites

2‐Hydroxyethyl methacrylate (HEMA) solution (1–10 wt %) was prepared in methanol and phosphate glass fibers were immersed in that solution for 5 min before being cured (irradiation time: 30 min) under UV radiation. Maximum polymer loading (HEMA content) was found for the 5 wt % HEMA solution. Degradation tests of the fibers in aqueous medium at 37°C suggested that the degradation of the HEMA‐treated fibers was lower than that of the untreated fibers. X‐ray photoelectron spectroscopy revealed that HEMA was present on the surface of the fibers. Using 5 wt % HEMA‐treated fibers, poly(caprolactone) matrix unidirectional composites were fabricated by in situ polymerization and compression molding. For in situ polymerization, it was found that 5 wt % HEMA‐treated fiber‐based composites had higher bending strength (13.8% greater) and modulus (14.0% greater) than those of the control composites. For compression molded composites, the bending strength and modulus values for the HEMA‐treated samples were found to be 27.0 and 31.5% higher, respectively, than the control samples. The tensile strength, tensile modulus, and impact strength of the HEMA composites found significant improvement than that of the untreated composites. The composites were investigated by scanning electron microscopy after 6 weeks of degradation in water at 37°C. It was found that HEMA‐treated fibers inside the composite retained much of their original integrity while the control samples degraded significantly. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Part 7. Effects of poly(L‐lactide‐co‐ϵ‐caprolactone) on morphology,structure, crystallization,and physical properties of blends of poly(L‐lactide) and poly(ϵ‐caprolactone)

Blended films of poly(L ‐lactide) [ie poly(L ‐lactic acid)] (PLLA) and poly(?‐caprolactone) (PCL) without or mixed with 10 wt% poly(L ‐lactide‐co‐?‐caprolactone) (PLLA‐CL) were prepared by solution‐casting. The effects of PLLA‐CL on the morphology, phase structure, crystallization, and mechanical properties of films have been investigated using polarization optical microscopy, scanning electron microscopy, differential scanning calorimetry and tensile testing. Addition of PLLA‐CL decreased number densities of spherulites in PLLA and PCL films, and improved the observability of spherulites and the smoothness of cross‐section of the PLLA/PCL blend film. The melting temperatures (T_m) of PLLA and PCL in the films remained unchanged upon addition of PLLA‐CL, while the crystallinities of PLLA and PCL increased at PLLA contents [X_PLLA = weight of PLLA/(weight of PLLA and PCL)] of 0.4–0.7 and at most of the X_PLLA values, respectively. The addition of PLLA‐CL improved the tensile strength and the Young modulus of the films at X_PLLA of 0.5–0.8 and of 0–0.1 and 0.5–0.8, respectively, and the elongation at break of the films at all the X_PLLA values. These findings strongly suggest that PLLA‐CL was miscible with PLLA and PCL, and that the dissolved PLLA‐CL in PLLA‐rich and PCL‐rich phases increased the compatibility between these two phases. © 2003 Society of Chemical Industry