Water Vapor Permeability of Poly(L‐lactide)/Poly(D‐lactide) Stereocomplexes

PLLA/PDLA blend films with only stereocomplex crystallites as a crystalline species together with pure PLLA and PDLA films with only homo‐crystallites as a crystalline species were prepared, and the effects of enantiomeric polymer blending, crystalline species, and crystallinity on the water vapor permeability were investigated. The WVT coefficient P of PLLA/PDLA blend films was 14–23% lower than that of pure PLLA and PDLA films in the crystallinity X_c range of 0–30%. Amorphous PLLA/PDLA blend films have a much lower P than pure PLLA and PDLA films. The dependence of P on X_c for blend films was stronger for X_c = 0–30% than for X_c = 30–100%. This dependence is discussed using the Nielsen model and the concept of “restricted” (or “restrained”) and “free” amorphous regions.

     

Poly(l‐lactide)/four‐armed star poly(l‐lactide)‐grafted multiwalled carbon nanotubes nanocomposites: Preparation,rheology, crystallization,and mechanical properties

Four‐armed star poly(l ‐ lactide)‐grafted multiwalled carbon nanotubes (CNTs‐g‐4PLLA) were synthesized through the nucleophilic substitution reaction between 4PLLA and acryl chloride of CNTs and then characterized by transmission electron microscope, X‐ray photoelectron spectroscopy, thermal gravimetric analysis (TGA), and ultraviolet visible spectrophotometer. The results indicated that 4PLLA was successfully grafted onto CNTs, and CNTs‐g‐4PLLA contained 37.7 wt% of 4PLLA. PLLA/CNTs‐g‐4PLLA nanocomposites were prepared by solution casting with different CNTs‐g‐4PLLA content. Rheological behavior of PLLA/CNTs‐g‐4PLLA nanocomposites was measured using a rheometer. The result showed that CNTs‐g‐4PLLA formed a network structure at percolation concentration, which improves obviously rheological properties of PLLA in the molten state. The crystallization behavior and crystal structure of the nanocomposites were comprehensive evaluated through differential scanning calorimetry, X‐ray diffraction, and polarizing optical microscope. The results found that CNTs‐g‐4PLLA played two roles in PLLA crystallization. The addition of CNTs‐g‐4PLLA acted as nucleating agent and obviously accelerated the spherulites growth under percolation concentration, while it inhibited the movement of PLLA chains at above percolation concentration, resulting in the decrease of crystallinity. Thermal stability and mechanical properties of the nanocomposites were also investigated using TGA, dynamic mechanical analysis, and tensile test. These results indicated that the incorporation of CNT‐g‐4PLLA into the PLLA matrix improved the thermal stability, storage modulus, and tensile strength of the nanocomposites. POLYM. COMPOS., 37:2744–2755, 2016. © 2015 Society of Plastics Engineers     

Poly(L‐lactide)/polypropylene blends: Evaluation of mechanical,thermal, and morphological characteristics

Poly(L lactide) (PLA) was blended with polypropylene (PP) at various ratios (PLA:PP = 90 : 10, 80 : 20, 70 : 30, and 50 : 50) with a melt‐blending technique in an attempt to improve the melt processability of PLA. Maleic anhydride (MAH)‐grafted PP and glycidyl methacrylate were used as the reactive compatibilizers to induce miscibility in the blend. The PLA/PP blend at a blend ratio of 90 : 10, exhibited optimum mechanical performance. Differential scanning calorimetry and thermogravimetric analysis studies showed that the PLA/PP/MAH‐g‐PP blend had the maximum thermal stability with the support of the heat deflection temperature values. Furthermore, dynamic mechanical analysis findings revealed an increase in the glass‐transition temperature and storage modulus with the addition of MAH‐g‐PP compatibilizer. The interaction between the compatibilizers and constituent polymers was confirmed from Fourier transform infrared spectra, and scanning electron microscopy of impact‐fractured samples showed that the soft PP phase was dispersed within the PLA matrix, and a decrease in the domain size of the dispersed phase was observed with the incorporation of MAH‐g‐PP, which acted as a compatibilizer to improve the compatibility between PLA and PP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Plasticization of Poly‐L‐lactide with L‐lactide,D‐lactide,and D,L‐lactide monomers

Poly‐L ‐lactide (PLLA) is being widely considered for repair of damaged tissues, for controlled antibiotic release, and also as scaffolds for cultured cells. PLLA was blended with the lactide monomer in its two enantiomeric forms: D ‐lactide (D ‐la) and L ‐lactide (L ‐la) and with the cyclic dimmer D ,L ‐la, in order to enhance its flexibility and thereby overcome its inherent problem of brittleness. In this work, the crystallization, phase structure, and tensile properties of PLLA and PLLA plasticized with 5, 10, 15, and 20 wt% of D ‐la, L ‐la, and D ,L ‐la are explored. The three plasticizers used were effective in lowering the glass transition temperature (T_g) and the melting temperature (T_m) of PLLA, around 20°C for a plasticizer content of 20 wt%. The tensile strength and modulus of the blends decreased following the increasing content of plasticizers from approximately 58 MPa to values below 20 MPa, and from 1667 to 200 MPa, respectively. Aging the blends at storage ambient temperature revealed that the enhanced flexibility as well as the morphological stability was lost over time due to the migration of the plasticizer to the surface, this being less marked in the case of D ‐la as a result of interactions between the polymer and its enantiomeric monomer of complementary configuration. POLYM. ENG. SCI., 53:2073–2080, 2013. © 2013 Society of Plastics Engineers     

The dispersion behavior of clay particles in poly(L‐lactide)/organo‐modified montmorillonite hybrid systems

Hybrids of poly(L‐lactide)/organoclay (PLACHs) have been prepared via a melt‐compounding process using poly(L‐lactide) (PLLA) and three types of surface‐treated montmorillonite modified with ammonium salts (M1, trimethyl octadecyl‐; M2, dimethyl dioctadecyl‐, and M3, bis(4‐hydroxy butyl) methyl octadecyl‐ammonium). The dispersed state of the clay particles in the PLLA matrix was examined by use of wide‐angle X‐ray diffraction, transmission electron microscopy, and polarizing optical microscopy. On melt‐compounding PLLA and two organoclays (M1, M2) modified with the surfactants both carrying homogenous alkyl chains, we obtained intercalated hybrids with relatively uniform dispersion of nanometer‐sized clay particles. On the other hand, the organoclay (M3) modified with a surfactant carrying alkyl chains end‐capped with hydroxyl groups yielded the composite with flocculated particles. The flocculation of the particles originates from the hydrogen bonding among the hydroxyl groups of the component surfactant, those of the clay edge and those of both ends of PLLA chains. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2711–2720, 2004     

Thermomechanical and optical properties of biodegradable poly(L‐lactide)/silica nanocomposites by melt compounding

Poly(L ‐lactide) (PLA)/silica (SiO₂) nanocomposites containing 1, 3, 5, 7, and 10 wt % SiO₂ nanoparticles were prepared by melt compounding in a Haake mixer. The phase morphology, thermomechanical properties, and optical transparency were investigated and compared to those of neat PLA. Scanning electron microscopy results show that the SiO₂ nanoparticles were uniformly distributed in the PLA matrix for filler contents below 5 wt %, whereas some aggregates were detected with further increasing filler concentration. Differential scanning calorimetry analysis revealed that the addition of SiO₂ nanoparticles not only remarkably accelerated the crystallization speed but also largely improved the crystallinity of PLA. An initial increase followed by a decrease with higher filler loadings for the storage modulus and glass‐transition temperature were observed according to dynamic mechanical analysis results. Hydrogen bonding interaction involving C?O of PLA with Si? OH of SiO₂ was evidenced by Fourier transform infrared analysis for the first time. From the mechanical tests, we found that the tensile strength and modulus values of the nanocomposites were greatly enhanced by the incorporation of inorganic SiO₂ nanoparticles, and the elongation at break and impact strength were slightly improved. The optical transparency of the nanocomposites was excellent, and it seemed independent of the SiO₂ concentration; this was mainly attributed to the closed refractive indices between the PLA matrix and nanofillers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Biodegradable poly(L‐lactic acid)/TiO2 nanocomposites: Thermal properties and degradation

Poly(L ‐lactic acid)‐titanium dioxide nanocomposites (with various loadings of TiO₂: 0.5, 1, 2, 5, and 10 wt %) were produced by solution casting method. The influence of TiO₂ on thermal properties and crystallinity of PLA was investigated by DSC and FTIR spectroscopy. The TiO₂ nano filler has no significant influence on the characteristic temperatures (T_g, T_c, and T_m), but has high impact on the crystallinity of these systems. The degree of crystallinity X_c significantly increases for PLA nanocomposites loaded with up to 5 wt % of TiO₂, while for 10 wt % load of TiO₂ it drops below X_c of the pure resin. The degradation of the prepared composites was evaluated hydrolytically in 1N NaOH, enzymatically in α‐amylase solutions, and under UV irradiation. The catalytic effect of TiO₂ nano particles on the degradation processes under UV light exposure (λ = 365 nm) and hydrolytic degradation was confirmed with the increase of the filler content. The opposite effect was identified in enzymatic degradation experiments. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology,rheological, crystallization behavior,and mechanical properties of poly(L‐lactide)/ethylene‐co‐vinyl acetate blends with different VA contents

Poly(L‐lactide)/ethylene‐co‐vinyl acetate (PLLA/EVA) blends with different contents of Vinyl Acetate (VA) in EVA phase were prepared through melt blending process. Although the composition of the blends was invariant (70/30), different phase morphologies were observed, namely, sea‐island morphologies for the blends with VA contents of 7.5, 18, and 28 wt %, whereas approximate co‐continuous morphology for the blend with VA content of 40 wt % was observed. The interfacial interaction between PLLA and EVA was visualized by Fourier transform infrared and rheological measurements. The nonisothermal and isothermal crystallization behaviors of the blends were investigated by wide angle X‐ray diffraction, Differential scanning calorimetry, and polarization optical microscope. Post‐thermal treatment was applied to improve the crystalline structure of PLLA. The results show that all the samples are mainly in amorphous state during the injection molding process. However, annealing promotes the second crystallization of PLLA matrix, leading to the improvement of the crystalline structure. Especially, the effect of annealing on crystalline structure of PLLA matrix is greatly dependent on the VA content of EVA. As expected, addition of EVA results in the improvement of the ductility and fracture toughness of the blends. The decreased tensile modulus and tensile strength can be enhanced through annealing process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Properties and morphology of poly(L‐lactide)/clay composites according to the clay modification

Montmorillonite (MMT) was modified with dodecylamine, 1,12‐diaminododecane, and 1,11‐aminoundecanoic acid to prepare CHMMT, NHMMT, and COMMT, respectively. The three clays were mixed with poly(L ‐lactide) (PLLA) with the aid of chloroform. Depending on the modifiers, PLLA/MMT composites exhibited different mechanical properties and morphology. A completely exfoliated morphology was observed in the PLLA/COMMT composite (PLACO). The PLACO exhibited the best tensile properties among the tested composites because of the finest dispersion of the clay layers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4983–4988, 2006     

Thermal and mechanical properties of plasticized poly(L‐lactide) nanocomposites with organo‐modified montmorillonites

Nanocomposites of poly(lactide) (PLA) and the PLA plasticized with diglycerine tetraacetate (PL‐710) and ethylene glycol oligomer containing organo‐modified montmorillonites (ODA‐M and PGS‐M) by the protonated ammonium cations of octadecylamine and poly(ethylene glycol) stearylamine were prepared by melt intercalation method. In the X‐ray diffraction analysis, the PLA/ODA‐M and plasticized PLA/ODA‐M composites showed a clear enlargement of the difference of interlayer spacing between the composite and clay itself, indicating the formation of intercalated nanocomposite. However, a little enlargement of the interlayer spacing was observed for the PLA/PGS‐M and plasticized PLA/PGS‐M composites. From morphological studies using transmission electron microscopy, a finer dispersion of clay was observed for PLA/ODA‐M composite than PLA/PGS‐M composite and all the composites using the plasticized PLA. The PLA and PLA/PL‐710 composites containing ODA‐M showed a higher tensile strength and modulus than the corresponding composites with PGS‐M. The PLA/PL‐710 (10 wt %) composite containing ODA‐M showed considerably higher elongation at break than the pristine plasticized PLA, and had a comparable tensile modulus to pure PLA. The glass transition temperature (T_g) of the composites decreased with increasing plasticizer. The addition of the clays did not cause a significant increase of T_g. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Poly(ε-caprolactone)/clay nanocomposites prepared by melt intercalation: mechanical, thermal and rheological properties

(Nano)composites of poly(ε-caprolactone) (PCL) were prepared by melt blending the polymer with natural Na⁺ montmorillonite and montmorillonite modified by hydrogenated tallowalkyl (HTA)-based quaternary ammonium cations, such as dimethyl 2-ethylhexyl HTA ammonium and methyl bis(2-hydroxyethyl) HTA ammonium. Microcomposites or nanocomposites were prepared depending on whether neat or modified montmorillonites was used, as assessed by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were studied as a function of the filler content by tensile testing, Izod impact testing, thermogravimetric analysis and differential scanning calorimetry. The rheological behaviour at 80 °C was also analysed in relation to the structure and content of the layered silicate. Effect of exfoliated silicates on the mechanical properties, thermal stability and flame resistance of PCL was considered. Stiffness and thermal stability improved with the filler loading until a content of 5 wt%. Further loading resulted in the levelling off and possibly in a decrease of these properties. A marked charring effect was observed upon exposure to a flame.     

Enhanced degradation of poly(L‐lactide) containing arginine,tryptophan and lysine

Addition of arginine, tryptophan and lysine to poly(L ‐lactide) (PLLA) has resulted in a new series of enhanced degradation biomaterials. Degradation was performed at 70°C and degradation behavior was studied using water uptake, mass loss, pH value change, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile properties. The results indicated that PLLA containing amino acids degraded more quickly than pure PLLA. In PLLA containing arginine, lysine, or tryptophan, crystallinity of the latter decreased after 8 days degradation while crystallinities of the other two composites increased. Destroying crystallites assists with deeper degradation and in vivo assimilation. Initial tensile strengths of all undegraded bars were almost the same. Furthermore, pH value changes indicated that additive amino acids could neutralize acidic degradation products, which may be a solution to the bacteria‐free inflammation induced by the acidic products. The results indicate that the composite biomaterials may be useful for future clinical application. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Poly(ethylene-oxide)/clay/silica nanocomposites: Morphology and thermomechanical properties

Poly(ethylene-oxide) PEO/clay/silica nanocomposites were prepared via solution intercalation by exploiting phase separation based on the bridging of particles by polymer chains. The intercalated morphology of nanocomposites was confirmed by XRD. Vibrational modes of the ether oxygen of PEO in the hybrids are shifted due to the coordination of the ether oxygen with the sodium cations of clay and the H-bonding interactions of the ether oxygen with the surface silanols of hydrophilic fumed silica. Based on SEM, the overall density of nanoparticle aggregates in the interspherulitic region was observed to be higher compared to that inside spherulites. PEO/clay/silica hybrids show significant property improvements compared to PEO/clay hybrids and pure PEO. The system containing 10 wt.% clay and 5 wt.% silica has substantially higher modulus and much lower crystallinity compared to the 15 wt.% clay system. The physics behind the reinforcement effect and the reduction of crystallinity as a function of fumed silica loading is discussed based on the morphological characterization of the hybrids. Lastly, PEO/clay/silica hybrids display good thermal stability and are much stiffer compared to pure PEO and PEO/clay nanocomposites.     

Preparation and structure and mechanical properties of poly(styrene‐b‐butadiene)/clay nanocomposites

Star‐shaped and linear block thermoplastic poly(styrene‐b‐butadiene) copolymer (SBS)/organophilic montmorillonite clays (OMMT) were prepared by a solution approach. The intercalation spacing in the nanocomposites and the degree of dispersion of nanocomposites were investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The mechanical properties, dynamic mechanical properties, and thermal stability of these nanocomposites were determined. Results showed that SBS chains were well intercalated into the clay galleries and an intercalated nanocomposite was obtained. The mechanical strength of nanocomposites with the star‐shaped SBS/OMMT were significantly increased. The addition of OMMT also gave an increase of the elongation, the dynamic storage modulus, the dynamic loss modulus, and the thermal stability of nanocomposites. The increase of the elongation of nanocomposites indicates that SBS has retained good elasticity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3430–3434, 2004     

Isothermal crystallization behavior of poly(L‐lactic acid)/organo‐montmorillonite nanocomposites

The isothermal crystallization behavior of poly(L ‐lactic acid)/organo‐montmorillonite nanocomposites (PLLA/OMMT) with different content of OMMT, using a kind of twice‐functionalized organoclay (TFC), prepared by melt intercalation process has been investigated by optical depolarizer. In isothermal crystallization from melt, the induction periods (t_i) and half times for overall PLLA crystallization (100°C ≤ T_c ≤ 120°C) were affected by the temperature and the content of TFC in nanocomposites. The kinetic of isothermal crystallization of PLLA/TFC nanocomposites was studied by Avrami theory. Also, polarized optical photomicrographs supplied a direct way to know the role of TFC in PLLA isothermal crystallization process. Wide angle X‐ray diffraction (WAXD) patterns showed the nanostructure of PLLA/TFC material, and the PLLA crystalline integrality was changed as the presence of TFC. Adding TFC led to the decrease of equilibrium melting point of nanocomposites, indicating that the layered structure of clay restricted the full formation of crystalline structure of polymer. The specific interaction between PLLA and TFC was characterized by the Flory‐Huggins interaction parameter (B), which was determined by the equilibrium melting point depression of nanocomposites. The final values of B showed that PLLA was more compatible with TFC than normal OMMT. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Effect of alkylammonium salt on the dispersion and properties of Poly(p‐phenylene sulfide)/clay nanocomposites via melt intercalation

To explore the possibility of making poly(p‐phenylene sulfide) (PPS) nanocomposites via melt intercalation and improving the mechanical properties of PPS, in this study we first modified clay (montmorillonite) with alkylammonium salt by cation exchange and then mixed the modified clay together with the PPS matrix by twin‐screw extrusion. Because the PPS/clay composites were made at a high temperature (300°C), thermogravimetric analysis experiments were carried out first to check the thermal stability of the alkylammonium salt treated clay and the obtained composites. Possible degradation of the alkylammonium salt during processing caused a decrease in the interlayer spacing of the clay. Scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction were used to investigate the dispersion of the clay sheet in the matrix. The clay layers were homogeneously dispersed in the PPS matrix with a nanometer scale, and an exfoliated structure was achieved at a low load of clay. The alkylammonium salt modifier enhanced the interaction between the PPS and clay on the one hand, but on the other hand, it also acted as a plasticizer and caused decreases in the glass‐transition temperature and tensile properties. More work is needed to find a modifier and processing conditions by which the modifier can help the dispersion of clay and also be completely degraded after the formation of an exfoliated structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1724–1731, 2006     

Crystallization behavior and mechanical properties of poly(ethylene oxide)/poly(L‐lactide)/poly(vinyl acetate) blends

Poly(vinyl acetate) (PVAc) was added to the crystalline blends of poly(ethylene oxide) (PEO) and poly(L ‐lactide) (PLLA) (40/60) of higher molecular weights, whereas diblock and triblock poly(ethylene glycol)–poly(L ‐lactide) copolymers were added to the same blend of moderate molecular weights. The crystallization rate of PLLA of the blend containing PVAc was reduced, as evidenced by X‐ray diffraction measurement. A ringed spherulite morphology of PLLA was observed in the PEO/PLLA/PVAc blend, attributed to the presence of twisted lamellae, and the morphology was affected by the amount of PVAc. A steady increase in the elongation at break in the solution blend with an increase in the PVAc content was observed. The melting behavior of PLLA and PEO in the PEO/PLLA/block copolymer blends was not greatly affected by the block copolymer, and the average size of the dispersed PEO domain was not significantly changed by the block copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3618–3626, 2001     

Isothermal crystallization of poly(ethylene‐co‐glycidyl methacrylate)/clay nanocomposites

Poly(ethylene‐co‐glycidyl methacrylate) (PEGMA)/clay nanocomposites with clay concentrations of 1, 3, or 5 wt % were prepared via y melt blending in a twin‐screw extruder. Wide‐angle X‐ray diffraction showed that the clay layers were intercalated by PEGMA. Differential scanning calorimetry was used to analyze the isothermal crystallization, and the equilibrium melting temperature was determined with the Hoffman–Weeks method. The Avrami, Tobin, Malkin, and Urbanovici–Segal models were applied to describe the kinetics of crystallization from the melt state under isothermal conditions. The crystallization kinetics showed that the addition of clay facilitated the crystallization of PEGMA, with the clay functioning as a heterophase nucleating agent; at higher concentrations, however, the physical hindrance of the clay layers to the motion of PEGMA chains retarded the crystallization process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1051–1064, 2005     

Nonisothermal crystallization of poly(ethylene‐co‐glycidyl methacrylate)/clay nanocomposites

The nonisothermal crystallization of poly(ethylene‐co‐glycidyl methacrylate) (PEGMA) and PEGMA/clay were studied by differential scanning calorimeter, at various cooling rates. Avrami model modified by Jeziorny, Ozawa mode and Liu model could successfully describe the nonisothermal crystallization process. Augis–Bennett model, Kissinger model, Takhor model, and Ziabicki model were used to evaluate the activation energy of both samples. It was found that the activation energy of PEGMA/clay nanocomposite was higher than that of neat PEGMA. Experimental results also indicated that the addition of modified clay might retard the overall nonisothermal crystallization process of PEGMA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1335–1343, 2006