Rheology and biodegradation of polylactide/silica nanocomposites

Silica‐filled polylactide (PLA) nanocomposites were prepared by melt compounding. The oscillatory rheological properties and biodegradation behavior were then investigated. As the silica loadings reach up to 5 wt%, percolated silica network structures form. For the percolated PLA/silica nanocomposites sample (the silica content was >5 wt%), the modulus enhances with an increase of temperature evidently. Moreover, it is interesting to find that the biodegradation rates have been enhanced obviously in the PLA/silica nanocomposites than in neat PLA. The erosion mechanism of neat PLA and the PLA/silica nanocomposites was further discussed. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Effects of thermoplastic poly(ether-ester) elastomer and bentonite nanoclay on properties of poly(lactic acid)

This work presented the influence of thermoplastic poly(ether-ester) elastomer (TPEE) and bentonite (BTN) on improving the mechanical and thermal properties of poly(lactic acid) (PLA). PLA was initially melt mixed with TPEE at six different loadings (5–30 wt%) on a twin screw extruder and then injection molded. The mechanical tests revealed an increasing impact strength and elongation at break with increasing TPEE loading, but a diminishing Young's modulus and tensile strength with respect to pure PLA. The blend at 30 wt% TPEE provided the optimum improvement in toughness, exhibiting an increase in the impact strength and elongation at break by 3.21- and 10.62-fold over those of the pure PLA, respectively. Scanning electron microscopy analysis illustrated a ductile fractured surface of the blends with the small dispersed TPEE domains in PLA matrix, indicating their immiscibility. The 70/30 (wt/wt) PLA/TPEE blend was subsequently filled with three loadings of BTN (1, 3, and 5 parts by weight per hundred of blend resin [phr]), where the impact strength, Young's modulus, tensile strength and thermal stability of all the blends were improved, while the elongation at break was deteriorated. Among the three nanocomposites, that with 1 phr BTN formed exfoliated structure and so exhibited the highest impact strength, elongation at break, and tensile strength compared to the other intercalated nanocomposites. Moreover, the addition of BTN was found to increase the thermal stability of the neat PLA/TPEE blend due to the barrier properties and high thermal stability of BTN.     

New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology

Our continuing research on the preparation, characterization, materials properties, and biodegradability of polylactide (PLA)-layered silicate nanocomposites has yielded results for PLA-montmorillonite nanocomposites. Montmorillonite modified with trimethyl octadecylammonium cation was used as an organically modified layered silicate for the nanocomposites preparation. The internal structure of the nanocomposites in the nanometer range has been established by using wide-angle X-ray diffraction and transmission electron microscope analyses. All the nanocomposites exhibited superior improvement of practical materials properties such as storage modulus, flexural modulus, flexural strength, heat distortion temperature, and gas barrier property as compared to that of neat PLA. The biodegradability of neat PLA and a representative nanocomposite was also studied under compost, and the rate of biodegradation of neat PLA significantly increased after nanocomposites preparation. The melt rheology of neat PLA and various PLACNs was also studied.     

Morphology, thermal, and viscoelastic properties of poly(glycidyl methacrylate-co-methyl methacrylate)-based nanocomposites with various organo-modified clays

New nanocomposites of poly(glycidyl methacrylate-co-methyl methacrylate) (PGM) cured with cyclohexanedicarboxylic anhydride (CDCA) and layered silicates of inorganic content 3 and 5 wt% were prepared by casting the solution of the mixture and subsequent cross-linking at finally 200 °C. Non-modified montmorillonite (MMT) and organo-MMTs (ODA-M, ALA-M, LEA-M, and HBP-M) modified with octadecylamine, 12-aminolauric acid, N-lauryldiethanolamine, and hexadecyltributylphosphonium bromide, respectively, were used as layered silicates. X-ray diffraction and morphological studies using transmission electron microscopy revealed that the highly intercalated nanocomposites with the interlayer spacing more than 5.5 nm are formed for the PGM-CDCA/ODA-M, LEA-M, and HBP-M composites with inorganic content 3 wt%. When the inorganic content was increased from 3 to 5 wt%, the degree of intercalation of all the PGM-CDCA/organoclay composites was lowered. Dynamic viscoelastic measurement revealed that the organoclay nanocomposites have significantly higher storage modulus than the PGM-CDCA neat resin. The thermogravimetric analysis revealed that the HBP-M composite with inorganic content 5 wt% has the highest thermal decomposition temperature.     

Polylactide,nanoclay, and core–shell rubber composites

Three types of composites, namely, polylactide (PLA)/nanoclay, PLA/core–shell rubber, and PLA/nanoclay/core–shell rubber, were melt compounded via a corotating twin‐screw extruder. The effects of two types of organically modified montmorillonite nanoclays (i.e., Cloisite®30B and 20A), two types of core (polybutylacrylate)–shell (polymethylmethacrylate) rubbers (i.e., Paraloid EXL2330 and EXL2314), and the combination of nanoclay and rubber on the mechanical and thermal properties of the composites were investigated. According to X‐ray diffraction and transmission electron microscopy analyses, both types of PLA/5 wt% nanoclay composites had an intercalated morphology. In comparison with pure PLA, both types of PLA/5 wt% nanoclay composites had an increased modulus, similar impact strength, slightly reduced tensile strength, and significantly reduced strain at break. On the other hand, PLA/EXL2330 composites with a rubber loading level of 10 wt% or higher had a much higher impact strength and strain at break, but a lower modulus and strength when compared with pure PLA. The simultaneous addition of 5 wt% nanoclay (Cloisite®30B) and 20 wt% EXL2330 resulted in a PLA composite with a 134% increase in impact strength, a 6% increase in strain at break, a similar modulus, and a 28% reduction in tensile strength in comparison with pure PLA. POLYM. ENG. SCI. 46:1419–1427, 2006. © 2006 Society of Plastics Engineers     

Thermo-physical and impact properties of epoxy nanocomposites reinforced by single-wall carbon nanotubes

The thermo-physical properties and the impact strength of diglycidyl ether of bisphenol F (DGEBF) epoxy nanocomposites reinforced with fluorinated single-wall carbon nanotubes (FSWCNT) are reported. A sonication technique was used to disperse FSWCNT in the glassy epoxy network resulting in nanocomposites having large improvement in modulus with extremely small amount of FSWCNT. The glass transition temperature decreased approximately 30 °C with an addition of 0.2 wt% (0.14 vol%) FSWCNT, without adjusting the amount of the anhydride curing agent. This was because of non-stoichiometry of the epoxy matrix that was caused by the fluorine on the single-wall carbon nanotubes. The correct amount of the anhydride curing agent needed to achieve stoichiometry was experimentally examined by dynamic mechanical analysis (DMA). The storage modulus of the epoxy at room temperature (which is below the glass transition temperature of the nanocomposites) increased up to 0.63 GPa with the addition of only 0.30 wt% (0.21 vol%) of FSWCNT, representing an up to 20% improvement compared with the neat epoxy. The Izod impact strength slightly decreased when the amount of FSWCNT was increased to 0.3 wt%. The excellent improvement in the storage modulus was achieved without sacrificing impact strength.     

Carbon nanotubes induced crystallization of poly(ethylene terephthalate)

We have investigated the crystallization characteristics of melt compounded nanocomposites of poly(ethylene terephthalate) (PET) and single walled carbon nanotubes (SWNTs). Differential scanning calorimetry studies showed that SWNTs at weight fractions as low as 0.03 wt% enhance the rate of crystallization in PET, as the cooling nanocomposite melt crystallizes at a temperature 10 °C higher as compared to neat PET. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. WAXD showed oriented crystallization of PET induced by oriented SWNTs in a randomized PET melt, indicating the role of SWNTs as nucleating sites.     

Effects of thermoplastic polyurethane on the properties of poly(lactic acid)/organo‐montmorillonite nanocomposites based on novel vane extruder

Polylactic acid (PLA)/organo‐montmorillonite (OMMT) nanocomposites toughened with thermoplastic polyurethane (TPU) were prepared by melt‐compounding on a novel vane extruder (VE), which generates global dynamic elongational flow. In this work, the mechanical properties of the PLA/TPU/OMMT nanocomposites were evaluated by tensile, flexural, and tensile tests. The wide‐angle X‐ray diffraction and transmission electron microscopy results show that PLA/TPU/OMMT nanocomposites had clear intercalation and/or exfoliation structures. Moreover, the particles morphology of nanocomposites with the addition of TPU was investigated using high‐resolution scanning electronic microscopy. The results indicate that the spherical TPU particles dispersed in the PLA matrix, and the uniformity decreased with increasing TPU content (≤30%). Interestingly, there existed abundant filaments among amount of TPU droplets in composites with 30 and 40 wt% TPU. Furthermore, the thermal properties of the nanocomposites were examined with differential scanning calorimeter and dynamic mechanical analysis. The elongation at break and impact strength of the PLA/OMMT nanocomposites were increased significantly after addition of TPU. Specially, Elongation at break increased by 30 times, and notched impact strength improved 15 times when TPU loading was 40 wt%, compared with the neat PLA. Overall, the modified PLA nanocomposites can have greater application as a biodegradable material with enhanced mechanical properties. POLYM. ENG. SCI., 54:2292–2300, 2014. © 2013 Society of Plastics Engineers     

Structure and properties of poly(lactic acid)/poly(ε‐caprolactone) nanocomposites with kinetically induced nanoclay location

Poly(lactic acid)/poly(ε‐caprolactone)/organically modified montmorillonite (PLA/PCL/OMMT) nanocomposites were melt‐processed in a twin‐screw extruder under high shear conditions. As a result of the processing conditions employed, the OMMT layers located in the less compatible PCL phase in all the ternary nanocomposites. The morphology of the PLA/PCL blend evolved from “sea‐island” to co‐continuous upon the addition of OMMT. Both the X‐ray diffraction (XRD) and viscoelastic characterization suggested similar OMMT dispersion in the reference PLA binary and in the PLA/PCL ternary nanocomposites, regardless of its location in the PLA and PCL phase, respectively. The reinforcing effect of the organoclay was also similar. The addition of OMMT to the PLA/PCL blend fully compensated the loss in stiffness and oxygen barrier performance produced by PCL in PLA; the nanocomposite with 3% OMMT showed the same modulus and permeability values as those of pure PLA. Moreover, the ductile behavior (elongation at break > 80%) of the PLA/PCL blend remained constant even in the nanocomposite containing 5% OMMT. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43815.     

Rheology, phase morphology, mechanical, impact and thermal properties of polypropylene/metallocene catalysed ethylene 1-octene copolymer blends

Blends of a polypropylene (PP) and a metallocene catalysed ethylene-octene copolymer (EOC) were prepared using a single screw extruder fitted with a barrier screw design. The EOC used had 25 wt% 1-octene content and the weight fraction of EOC in the blends covered the range 1-30 wt.% Viscosity values for the blends determined experimentally from dual capillary rheological studies were similar to those calculated theoretically using the log additivity principle described by Ferry. This result together with scanning electron microscopy (SEM) observations and evidence from tan δ curves from dynamic mechanical thermal analysis showed PP and EOC to be partially miscible for blends having 10 wt% EOC or less. The tensile modulus, break strength and flexural modulus of the blends decreased with respect to virgin PP as the weight fraction of EOC was increased to 30 wt.% The diminution in mechanical properties was concomitant with an initial increase in elongation at break from 40% for neat PP to 140% for the blend with 15 wt% EOC before decreasing to 65% when 30 wt% EOC was blended. The optimum impact modification of the PP used in this study, in the temperature range −40 to 23 °C, was achieved by blending with between 20 and 30 wt% EOC.     

Preparation of nanocomposites by melt compounding polylactic acid/polyamide 12/organoclay at different screw rotating speeds using a twin screw extruder

This study analyzes the effect of different screw rotating speeds on the clay dispersion and mechanical properties of nanocomposites prepared by melt compounding polylactic acid (PLA) with an organoclay in a co‐rotating twin screw extruder. Polyamide 12 (PA12) was used as an additive. Two different screw rotating speeds, 65 rpm and 150 rpm, were used in this study. According to the tensile strength data, the Young's modulus of the PLA/clay nanocomposites showed improvement at a screw rotating speed of 150 rpm. The Young's modulus improved with the addition of the organoclay to PLA matrix, but decreased when PA12 was added to the PLA matrix. The tensile strengths and elongations become small by adding organoclay to PLA matrix. The tensile strengths of the PLA/organoclay nanocomposites increased for the higher screw rotating speed (150 rpm). The d‐spacing of PLA/PA12/Clay nanocomposites was independent of the addition of PA12. The size of the clay aggregates in the PLA/PA12/Clay nanocomposites is smaller than that of PLA/Clay. Furthermore, the thermal stability of the PLA/Clay nanocomposite increases with addition of PA12, while on the whole, it had little influence on the tensile properties. POLYM. COMPOS., 29:1–8, 2008. © 2007 Society of Plastics Engineers     

Synthesis of chain-extended organifier and properties of polyurethane/clay nanocomposites

Clay organifier with hydroxyl end-group and relatively high molecular weight was synthesized. The clay treated with the organifier was suspended in DMF and the dispersibility of organoclay in polyurethane matrix was enhanced by applying the sonication to the suspension of organoclay in DMF. The d-spacing of organoclay was found to be 2.29 nm compared to 1.18 nm of pristine montmorillonite. The polyurethane/clay nanocomposites formed an intercalated structure with some disorder and their d-spacings were about 2.6-2.7 nm. The barrier property, thermal stability and tensile properties significantly increased with increasing the dispersibility of organoclay. A 2.9-fold increase in tensile strength with 1 wt% of well-dispersed organoclay, a 41% decrease in oxygen permeability and a 1.7-fold increase in Young's modulus at 5 wt% of well-dispersed organoclay were achieved.     

Structure and properties of nanocomposites based on poly(butylene succinate) and organically modified montmorillonite

Poly(butylene succinate) and organically modified montmorillonite nanocomposites with there different compositions were prepared via melt blending in a twin‐screw extruder. The structure of the nanocomposites was studied with X‐ray diffraction and transmission electron microscopy, which revealed the formation of intercalated nanocomposites, regardless of the silicate loading. Dynamic mechanical analysis revealed a substantial increase in the storage modulus of the nanocomposites over the entire temperature range investigated. The tensile property measurements showed a relative increase in the stiffness with a simultaneous decrease in the yield strength in comparison with that of neat poly(butylene succinate). The oxygen gas barrier property of neat poly(butylene succinate) improved after nanocomposite preparation with organically modified montmorillonite. The effect of the layered‐silicate loading on the melt‐state linear viscoelastic behavior of the intercalated nanocomposites was also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 777–785, 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.     

Incorporation of Mg-Al hydrotalcite into a biodegradable Poly(ε-caprolactone) by high energy ball milling

The technique of high energy ball milling (HEBM) was used to prepare nanocomposites of poly(ε-caprolactone) (PCL) and an organically modified Mg-Al layered double hydroxide. The amount of inorganic material was varied from 0 to 6 wt%, and the samples were melted and quenched in ice-water after milling. The molecular weight of PCL decreased and its distribution increased as a consequence of milling. The structural analysis of the milled samples, conducted by X-ray diffraction and infrared absorption techniques, showed that the 12 hydroxydodecanoates organic modifier was still attached to the inorganic lamellae even if a partial delamination of the layered compounds occurred. The mechanical parameters (modulus, stress at yield point, strain at break point and stress at break values) derived from the stress-strain curves, improved in the composite samples containing up to 2.8 wt% of inorganic filler, with respect to the pure polymer, in spite of the molecular weight decrease. The thermodynamic diffusion coefficient of water vapor in composite samples was lower than in pure PCL, indicating an improvement of the barrier effect.     

Poly lactic acid nanocomposites containing modified nanoclay with synergistic barrier to water vapor for coated paper

The binary nanocomposites of poly lactic acid (PLA) with the montmorillonite modified with trisilanol polyhedral oligomeric silsesquioxanes (Trisilanolisooctyl POSS^®) were prepared via a solution‐blending process and coated on paper by bar coating and compress hot melt coating methods. The resulting components were characterized with Fourier transform infrared spectroscopy, and X‐ray diffraction (XRD) techniques. Moreover, the water vapor transmission rates (WVTR) for the coated writing paper were determined using an IGA‐003. The results indicated that the modified clay PLA nanocomposites enhanced the water vapor barrier properties of coated paper significantly. The permeability of PLA nanocomposites to water vapor decreased by 74% [26.0 g/(m² day)], respectively, as compared to those of the paper coated with pure PLA. The dispersion and phase behavior of the modified montmorillonite in PLA matrix was revealed by Transmission electron microscope. The intercalation of montmorillonite with PLA was further demonstrated using XRD. WVTR results indicated that the compress hot melt coating of the nanocomposites is an effective method to improve the water vapor resistance of coated paper. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40952.     

Processing and properties of PLA/thermoplastic starch/montmorillonite nanocomposites

Thermoplastic starch (TPS) and polylactic acid (PLA) were compounded with natural montmorillonite (MMT) using a twin‐screw extrusion process to investigate the structure and properties of these nanocomposites and to examine the use of water to enhance clay exfoliation. Tensile and essential work of fracture measurements were performed on standard dumbbell shape samples and on double notched samples to determine the effect of MMT and PLA/TPS interfacial modification on the mechanical and fracture properties of the materials. The nanocomposite structure was investigated using X‐Ray diffraction, transmission electron microscopy, and atomic force microscopy. Differential scanning calorimetric analysis was performed on the materials to determine the effect of TPS and MMT on PLA crystallization and physical aging. It was found that the TPS can intercalate the clay structure and that the clay was preferentially located in the TPS phase or at the blend interface. This led to an improvement in tensile modulus and strength and to a reduction in fracture toughness. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Rheological behavior of new melt compounded copolyamide nanocomposites

In this paper the rheological behavior of new polyamide-based nanocomposites produced by melt compounding using three different silicate loadings and screw speeds was investigated. The thermoplastic matrices selected were a polyamide 6 and its statistical copolymer having partially aromatic structure, whereas the clay was a commercial organo-modified montmorillonite. Hybrid systems were prepared by means of a laboratory-scale twin screw extruder and were submitted to rheological and structural investigations. The rheological experiments (dynamic frequency sweep, steady rate sweep and stress relaxation tests) were performed to evaluate the effect of both system composition (kind of matrix and clay content) and extrusion rate on the flow behavior of the nanocomposites. Rheology, that is highly sensitive to the nanoscale structure of the materials, put out a pseudo-solid like flow behavior at long times in the hybrids with silicate content higher than 6 wt% and produced with high extrusion rate; this response was related to the formation of an extended structural network across the polymer matrix due to strong polymer-silicate interactions that slow the relaxation times of the macromolecules. Corresponding to this behavior, TEM micrographs have shown a quite uniform dispersion of clay particles on micron-scale and a fair level of silicate exfoliation on nanoscale with a macroscopic preferential orientation of the layers in samples. The rheological measurements also reveal that this flow response is more marked for nanocomposites based on the copolyamide matrix, suggesting that this resin may have a higher silicate affinity respect to polyamide 6 homopolymer.     

Influence of screw speed on the mechanical and rheological properties of poly(ethylene‐co‐vinyl acetate)—organomodified montmorillonite nanocomposites

Poly(ethylene‐co‐vinyl acetate) (EVA) and organophilic montmorillonite clay nanocomposites were manufactured in a co‐rotating twin‐screw extruder using screw speeds ranging between 200 and 800 rpm. The morphology and thermal‐mechanical and rheological properties were studied to establish processing–morphology–property relationships. Particularly for samples produced under higher screw speed ranges, X‐ray diffraction and transmission electron microscopy revealed a tendency of increased exfoliated clay. Although the mechanical properties improved by the presence of clay, they were not altered by the screw speed. The rheological behavior in the solid and melt states were evaluated and showed that the storage modulus of neat EVA subjected to higher screw speed undergoes more pronounced decrease in the storage modulus than the nanocomposites, suggesting that the clay minimizes the effect of the screw speed. This minimization effect could be explained in the light of the assessment of relaxation times that showed stronger physical interactions with the nanocomposites in the molten state. POLYM. COMPOS., 36:854–860, 2015. © 2014 Society of Plastics Engineers     

Crystallization, structure and properties of plasticized poly(l-lactide)

Poly(l-lactide) (PLA) was plasticized with poly(ethylene glycol)s having M_w of 400 and 600 g/mol. In addition to poly(ethyne glycol)s with hydroxyl end groups, monomethyl ethers of poly(ethylene glycol) having M_w of 550 and 750 g/mol, with chains terminated with hydroxyl groups and methyl groups, were used. The effect of different end groups on the plasticization of both amorphous and semicrystalline PLA was studied. The crystallization, structure, thermal and tensile properties of PLA and PLA with 5 and 10 wt% of plasticizers were explored. No marked effect induced by different end groups of plasticizers was found. All the plasticizers used decreased T_g and increased the ability of PLA to cold crystallization. While an amorphous plasticized PLA could be deformed to about 550%, a semicrystalline PLA with the same total plasticizer content exhibited nonuniform plasticization of the amorphous phase and less ability to the plastic deformation. Nevertheless, a 20% elongation at break was achieved for a semicrystalline PLA with 10 wt% of the plasticizer. The plastic deformation of both neat and plasticized PLA was associated with crazing.