Preparation and crystallization behavior of polylactide nanocomposites reinforced with POSS-modified montmorillonite

We herein report the preparation and crystallization behavior of polylactide (PLA) nanocomposites reinforced with polyhedral oligomeric silsesquioxane-modified montmorillonite (POSS-MMT), which is prepared by exchanging sodium cations of pristine sodium montmorillonite (Na-MMT) with protonated aminopropylisobutyl polyhedral oligomeric silsesquioxane (POSS-NH₃ ⁺). PLA nanocomposites with 1–10 wt% POSS-MMT contents are manufactured via melt-compounding, and their structures and melt-crystallization behavior are investigated. It is characterized that POSS-MMT nanoparticles in the nanocomposites have an exfoliated structure of MMT silicates with POSS-NH₃ ⁺ and partial POSS-NH₂ crystals. DSC cooling thermograms suggest that the overall melt-crystallization rates of the nanocomposite with only 3 wt% POSS-MMT are remarkably enhanced in comparison with the neat PLA. From the isothermal crystallization analysis based on the Avrami model, the overall melt-crystallization of PLA/POSS-MMT nanocomposites is found to be dominated by the heterogeneous nucleation and three-dimensional spherulite growth. Isothermal melt-crystallization experiments using a polarized optical microscope show that the spherulite nucleation density of PLA/POSS-MMT nanocomposites is much higher than that of the neat PLA, whereas the spherulite growth rates of all the nanocomposites are almost identical with the rate of the neat PLA. It is concluded that the highly enhanced melt-crystallization rates of PLA/POSS-MMT nanocomposites stem from the dominant nucleation effect of POSS-MMT nanoparticles for PLA crystals.     

Thermal and structure properties of biobased cellulose nanowhiskers/poly (lactic acid) nanocomposites

Cellulose nanowhiskers were used to improve the performance of poly (lactic acid) (PLA). The nanocomposites mixed with three different molecular weight of poly (ethylene glycol) (PEG) were characterized by mechanical testing, thermal gravimetry and differential scanning calorimetry. The tensile test showed an increase in tensile strength and elongation at break with the addition of PEG to PLA/CNW nanocomposites, the thermal analysis results showed an increase of crystallization temperature (T _c) and crystallization compatibility (larger crystallization and melting areas), which indicated that the cellulose nanowhiskers (CNW) and PEG or CNW alone should not be considered as nucleating agents for the PLA matrix; The CNW was homo-dispersed which contributed to decreasing mobility of polymer chain segments. The compatibility between hydrophobic PLA matrix and the hydrophilic CNW was improved by the addition of different molecular weight polymeric-PEG. The thermo gravimetric analysis indicated that the thermal stability of the different composites were reflected well in the region between 25 °C and 245 oC. The structure of the PLA/CNW/PEG composites was characterized by AFM, which showed that the CNW dispersed in the PLA matrix evenly.     

Thermal properties of copolyetherester/silica nanocomposites

Thermal properties of copolyetherester/silica nanocomposites were examined by using DSC and TGA. The segmented block copolyetheresters with various hard segment structures and hard segment contents (HSC) were synthesized and their silica nanocomposite films were prepared by solution casting method. The nano-sized fumed silica particles were found to act as a nucleating agent of the copolyetheresters. The nanocomposites always showed reduced degree of supercooling or faster crystallization than the corresponding copolyetheresters. The nanocomposites also showed increased hard segment crystallinity except HSC 35 sample which had short hard segment length. In case of 2GT [poly(ethylene terephthalate)] copolyetheresters, which were not developed commercially because of their low crystallization rate, the hard segment crystallinity increased considerably. The copolyetherester/silica nanocomposites showed better thermal stability than copolyetheresters.     

Incorporation of surface modified graphene nanoplatelets for development of shape memory PLA nanocomposite

In this study, a temperature sensitive shape memory polymer (SMP) system based on polylactic acid (PLA) has been developed and the effect of graphene nanoplatelets (GNPs) on the shape memory properties was evaluated. Dispersion of GNPs in PLA was improved with the aid of a zwitterionic surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the surface modified graphene nanoplatelets (SMGNPs) were exfoliated and homogenously dispersed in the PLA matrix due to enhancement of the polymer-graphene interaction. Mechanical properties of the samples namely stiffness and elasticity were increased upon incorporation of graphene nanoplatelets accompanied by their good dispersion in the PLA matrix. Furthermore, differential scanning calorimetry (DSC) revealed that the nucleation effect of graphene promote the crystallization and noticeably enhanced the degree of crystallinity. Finally, prominent mechanical properties along with high degree of crystallization due to fine dispersion of surface modified graphenes, resulted in drastic improvement in shape memory performance.     

Enhanced mechanical and thermal properties of hybrid graphene nanoplatelets/multiwall carbon nanotubes reinforced polyethylene terephthalate nanocomposites

The effects of graphene nanoplatelets (GNP) and multiwall carbon nanotube (MWCNT) hybrid nanofillers on the mechanical and thermal properties of reinforced polyethylene terephthalate (PET) have been investigated. The nanocomposites were melt blended using the counter rotating twin screw extruder followed by injection molding. Their morphology, mechanical and thermal properties were characterized. Combination of the two nanofillers in composites formulation supplemented each other which resulted in the overall improvement in adhesion between fillers and matrix. The mechanical properties and thermal stability of the hybrid nanocomposites (PET/GNP1.5/MWCNT1.5) were significantly improved compared to PET/GNP3 and PET/MWCNT3 single filer nanocomposites. However, it was observed that GNP was better in improving the mechanical properties but MWCNT resulted in higher thermal stability of Nanocomposite. The transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed uniform dispersion of the hybrid fillers in PET/GNP1.5/MWCNT1.5 nanocomposites while agglomeration was observed at higher filler content. The MWCNT prevented the phenomenal stacking of the GNPs by forming a bridge between adjacent GNP planes resulting in higher dispersion of fillers. This complimentary geometrical structure is responsible for the significant improvement in the thermal stability and mechanical properties of the hybrid nanocomposites.     

Effect of multi walled carbon nanotube on the crystalline structure of polypropylene fibers

Polypropylene fibers containing varying amounts of multi walled carbon nanotube (MWCNT) have been spun using a conventional melt spinning and drawing apparatus. Changes in morphology and crystalline structure of composite fibers induced by addition of MWCNT were studied by small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR) and birefringence measurements. The results of SAXS experiments showed an increase in lamellar thickness, long period and crystallinity of the composite fibers in comparison to pure polypropylene fibers. Molecular orientation and helical content of the fibers were increased due to the addition of MWCNT to the polypropylene matrix. WAXS results, being in agreement with the SAXS results, also showed an increase in crystallinity of the composite fibers due to the increase in MWCNT content. This is probably because of nucleating effect of nanotubes in the fiber matrix, causing more crystallization and orientation of molecules to take place around them.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

Preparation of new polymer nanocomposites based on poly(lactic acid)/fatty nitrogen compounds modified clay by a solution casting process

In this study, different organoclays (OMMTs) were prepared using various fatty nitrogen compounds (FNCs) and natural clay, sodium montmorillonite (MMT). The clay modification was carried out by stirring the clay particles in an aqueous solution of fatty amides (FA), fatty hydroxamic acids (FHA), and carbonyl difatty amides (CDFA). These OMMTs were then used for nanocomposites production to improve the property balance of poly(lactic acid) (PLA) by solution casting process. All sets of OMMTs and nanocomposites were characterized using various apparatuses. In the nanocomposites, where the clay surface is pretreated with FA, FHA and CDFA, the basal spacing of the clay increased to 2.94, 3.26 and 3.80 nm, respectively The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed the production of nanocomposites. PLA modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with pure PLA.     

Processing of microcellular nanocomposite foams by using a supercritical fluid

Polystyrene/layered silicate nanocomposites were prepared by melt intercalation. To examine the distribution of the clay in polymer matrix, small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used. Intercalated nanocomposites were obtained and their rheological properties were investigated. Microcellular nanocomposite foams were produced by using a supercritical fluid. As clay contents increased, the cell size decreased and the cell density increased. It was found that layered silicates could operate as heterogeneous nucleation sites. As the saturation pressure increased and the saturation temperature decreased, the cell size decreased and the cell density increased. Microcellular foams have different morphology depending upon the dispersion state of nanoclays.     

Polylactic acid/carbon fiber composites: Effects of functionalized elastomers on mechanical properties,thermal behavior,surface compatibility,and electrical characteristics

In this study, the maleic anhydride grafted styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MA) is used as the compatilizer for polylactic acid (PLA)/carbon fiber (CF) composites. The effects of SEBS-g-MA on the mechanical properties, thermal behavior, interfacial compatibility, and electrical characteristics of composites are then evaluated. The mechanical property tests indicate that when the amount of compatilizer increases, the tensile properties and flexural property of the composites decrease while their impact strength increases. The SEM results show that the compatilizer can decrease the interstices between PLA and CF, and thereby augments their interfacial compatibility. The differential scanning calorimetry (DSC) results confirm that the compatilizer results in a greater crystallization temperature and a greater crystallinity of the composites. The electrical characteristic results indicate that neither PLA nor SEBS-g-MA is not interfered with the conductive network that is constructed by CF, which is exemplified by an average electromagnetic shielding effect of above ?30 dB. This study confirms that SEBS-g-MA can improve interfacial compatibility and toughness, as well as attain good electrical characteristics of PLA/CF composites.     

Preparation and UV-protective property of PVAc/ZnO and PVAc/TiO<Subscript>2</Subscript> microcapsules/poly(lactic acid) nanocomposites

The poly(vinyl acetate) (PVAc)/zinc oxide (ZnO) microcapsule and PVAc/titanium dioxide (TiO₂) microcapsule were synthesized via in-situ emulsion polymerization method. The PVAc/ZnO microcapsule and PVAc/TiO₂ microcapsule were characterized by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis(TG), transmission electron microscopy (TEM), and UV-visible spectroscopy (UV-vis). Effect of PVAc/ZnO microcapsule and PVAc/TiO₂ microcapsule on properties of poly(lactic acid) (PLA) was evaluated by UV-vis, SEM and mechanical properties test. The results showed that the addition of PVAc/ZnO and PVAc/TiO₂ microcapsules as a UV-blocking additive could significantly enhance UV-blocking property of PLA/PVAc/ZnO microcapsule composites and PLA/PVAc/TiO₂ microcapsule composites compared with pure PLA, PLA/ZnO composites and PLA/TiO₂ composites. The mechanical properties of PLA/PVAc/ZnO microcapsule composites were better than those of PLA/ZnO composites due to good dispersability and compatibility of PVAc/ZnO microcapsule in PLA matrix. Also, the mechanical properties of PLA/PVAc/TiO₂ microcapsule composites were better than those of pure PLA and PLA/TiO₂ composites. This study demonstrates the great potentials of the intrinsically UV shield additive PVAc/ZnO and PVAc/TiO₂ microcapsules in the application of high performance matrix resin and composite material.     

New biopolymer nanocomposites based on epoxidized soybean oil plasticized poly(lactic acid)/fatty nitrogen compounds modified clay: Preparation and characterization

Biodegradable polymers, such as poly(lactic acid) (PLA) have attracted a lot of attention in the scientific community recently due to a rapid growth of intensive interest in the global environment for alternatives to petroleum-based polymeric materials. Fatty nitrogen compounds (FNCs), fatty amides (FA), fatty hydroxamic acids (FHA), and carbonyl difatty amides (CDFA), which were synthesized from vegetable oils, were used as one of organic compounds to modify natural clay (sodium montmorillonite). The clay modification was carried out by stirring the clay particles in an aqueous solution of FA, FHA, and CDFA, by which the clay layer thickness increased from 1.23 to 2.61, 2.84 and 3.19 nm, respectively. The modified clay was then used in the preparation of the PLA/epoxidized soybean oil (ESO) blend nanocomposites. They were prepared by incorporating 2% of CDFA-MMT and 3% of both FA-MMT and FHA-MMT. The interaction of the modifier in the clay layer was characterized by X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Elemental analysis was used to estimate the presence of FNCs in the clay. The nanocomposites were synthesized by solution casting of the modified clay and a PLA/ESO blend at the weight ratio of 80/20, which has the highest elongation at break. The XRD and transmission electron microscopy (TEM) results confirmed the production of nanocomposites. PLA/ESO modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with those of the PLA/ESO blend. The novelty of this study is use of FNCs which reduces the dependence on petroleum-based surfactants.     

Fabrication and Characterization of Poly(L-lactic Acid) Fiber Mats Using Centrifugal Spinning

Polylactic acid (PLA) fine fibers and multi walled carbon nanotube (MWCNT) reinforced PLA fine fiber composites were developed utilizing a centrifugal spinning process. Chloroform and chloroform combined with dimethylformamide (DMF) were used to prepare solutions with varying concentrations of PLA and MWCNTs. The optimum spinning conditions to produce PLA fibers and its composites were determined. The morphology of the fibers was analyzed using scanning electron microscopy. In addition, X-ray diffraction analysis and thermo-physical characterization was conducted using thermogravimetric analysis and differential scanning calorimetry. PLA fibers with an average diameter of 481 nanometers and PLA/MWCNT fibers with an average diameter of 358 nanometers were obtained. A decrease in the crystallinity of the fibers was observed when compared to bulk PLA values.     

Effect of conformation on the properties of uniaxially drawn polylacide films upon drawing temperature

Polylactide(PLA) films were drawn at various drawing temperature of 65, 90 and 120 °C. The effects of drawing temperature on structural conformation and properties of PLA films were investigated. It was confirmed that the PLA films at drawing temperature of 65 and 90 °C were composed of α′ phase crystal form. The strain-induced crystallization and molecular orientation increased with increasing the draw ratio, which result in improving the mechanical and thermal properties of α′ phase PLA films. However, at drawing temperature of 120 °C, the strain-induced crystallization and molecular orientation of PLA films were not distinctly detected. It was supposed that the rate of the chain relaxation was faster than chain orientation and strain-induced crystallization during uniaxial drawing process.     

Blends of polylactide/thermoplactic elastomer: Miscibility, physical aging and crystallization behaviors

The PLA/PAE blends with four different weight ratios were prepared by melt mixing. PLA and PAE in PLA/PAE blends were almost immiscible while the weak interaction between PLA and PAE existed. The sub-micrometer PAE domains were dispersed in PLA matrix uniformly. The physical aging of PLA could be inhibited by introducing PAE. For PLA/PAE, the structure formed by physical aging at room temperature induced the accelerated crystallization of PLA during heating. However, for neat PLA, the structure formed by physical aging had a negligible effect on the crystallization of PLA during heating. The isothermal crystallization kinetics of neat PLA and PLA/PAE were analyzed by Avrami theory. The values of Avrami exponent were within the range 2.1–3.0. The crystallization rate of PLA was enhanced significantly by addition of PAE.     

Properties of thermoplastic starch from cassava bagasse and cassava starch and their blends with poly (lactic acid)

Cassava bagasse is an inexpensive and broadly available waste byproduct from cassava starch production. It contains roughly 50% cassava starch along with mostly fiber and could be a valuable feedstock for various bioproducts. Cassava bagasse and cassava starch were used in this study to make fiber-reinforced thermoplastic starch (TPS_B and TPS_I, respectively). In addition, blends of poly (lactic acid) and TPS_I (20%) and TPS_B (5, 10, 15, 20%) were prepared as a means of producing low cost composite materials with good performance. The TPS and PLA blends were prepared by extrusion and their morphological, mechanical, spectral, and thermal properties were evaluated. The results showed the feasibility of obtaining thermoplastic starches from cassava bagasse. The presence of fiber in the bagasse acted as reinforcement in the TPS matrix and increased the maximum tensile strength (0.60 MPa) and the tensile modulus (41.6 MPa) compared to cassava starch TPS (0.40 and 2.04 MPa, respectively). As expected, blending TPS with PLA reduced the tensile strength (55.4 MPa) and modulus (2.4 GPa) of neat PLA. At higher TPS_B content (20%) the maximum strength (19.9 MPa) and tensile modulus (1.7 GPa) were reduced about 64% and 32%, respectively, compared to the PLA matrix. In comparison, the tensile strength (16.7) and modulus (1.2 GPa) of PLA blends made with TPS_I were reduced 70% and 51% respectively. The fiber from the cassava bagasse was considered a filler since no increase in tensile strength of PLA/TPS blends was observed. The TPS_I (33.1%) had higher elongation to break compared to both TPS_B (4.9%) and PLA (2.6%). The elongation to break increased from 2.6% to 14.5% by blending TPS_I with PLA. In contrast, elongation to break decreased slightly by blending TPS_B with PLA. Thermal analysis indicated there was some low level of interaction between PLA and TPS. In PLA/TPS_B blends, the TPS_B increased the crystallinity of the PLA component compared to neat PLA. The fiber component of TPS_B appeared to have a nucleating effect favoring PLA crystallization.     

Crystallization and Luminescence Properties of Polypropylene Fiber Containing Rare Earth Aluminates and a Sorbital Derivative Nucleating Agent

Polypropylene (PP) fibers with a sorbital derivative nucleating agent (SDN) and rare earth aluminates (SrAl₂O₄:Eu²⁺,Dy³⁺) were prepared via melt compounding and melt-spinning. Non-isothermal crystallization kinetics and luminescence properties of PP and luminous PP fibers were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and decay of the afterglow test. The crystallization temperature determined by DSC increased with the addition of the nucleating agent during the cooling process from 200 °C. The Jeziorny model successfully described the non-isothermal crystallization behavior of the luminous PP with various SDN contents. The crystal grain size and morphology of the sample with the SDN was different from that without nucleating agent. The luminous PP fabric having high initial brightness intensity, approximately 461 mcd g^-1m^-2, can be prepared with addition of 10 wt% of rare earth aluminates and 0.5 % of SDN.     

Degradation and rheological properties of biodegradable nanocomposites prepared by melt intercalation method

Biodegradable nanocomposites were prepared by mixing a polymer resin and layered silicates by the melt intercalation method. Internal structure of the nanocomposite was characterized by using the small angle X-ray scattering (SAXS) and transmission electron microscope (TEM). Nanocomposites having exfoliated and intercalated structures were obtained by employing two different organically modified nanoclays. Rheological properties in shear and extensional flows and biodegradability of nanocomposites were measured. In shear flow, shear thinning behavior and increased storage modulus were observed as the clay loading increased. In extensional flow, strain hardening behavior was observed in well dispersed system. Nanocomposites with the exfoliated structure had better biodegradability than nanocomposites with the intercalated structure or pure polymer.     

Structure,electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.     

Crystallization behaviour of PP and carbon nanofibre blends

Crystallization behaviour of blends of different MFI isotactic polypropylenes (PP), and blends of PP with carbon nanofibre have been investigated by DSC and polarizing optical microscope. Both higher MFI PP component and the carbon nanofibre in the blend influence the nucleation activity of the melt during non-isothermal crystallization. In presence of carbon nanofibre, the sherulitic growth rate is highly disturbed. The calculation of nucleation activity indicates that carbon nanofibres act as active substrate for heterogeneous nucleation.