Isothermal cold crystallization kinetics and properties of thermoformed poly(lactic acid) composites: effects of talc,calcium carbonate,cassava starch and silane coupling agents

Iranian Polymer Journal - The effects of three different fillers (i.e., talc, calcium carbonate, and cassava starch) and surface functionalization by 3-aminopropyltriethoxysilane (APTES) and...     

Effect of Type of Surfactants and Organoclay Loading on the Mechanical Properties of EVOH/Clay Nanocomposite Blown Films

EVOH/clay nanocomposite films were prepared by using four types of surfactants to treat surface of clay because the surfactants were expected to affect the degree of clay dispersion in the EVOH matrix, which would in turn affect the properties of film. The nanocomposite films that contained the single alkyl tail with two repeating units of oxyethylene surfactants or single alkyl tail surfactant showed higher tensile strength, tensile modulus and elongation at break than those with 15 repeating units of oxyethylene surfactants or those with double alkyl tail surfactant.     

Effects of size and shape of dispersed poly(butylene terephthalate) on isothermal crystallization kinetics and morphology of poly(lactic acid) blends

The isothermal crystallization kinetics and morphology of the poly(lactic acid) (PLA) blends containing three different sizes of both spherical and fibrous poly(butylene terephthalate) (PBT) domains have been comparatively investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The dynamic DSC measurement reveals that PBT domains significantly increase the degree of crystallinity of the PLA. Furthermore, the Avrami model is employed to evaluate the crystallization kinetics under isothermal conditions and it is found that PBT acts as nucleating agent, leading to a high overall crystallization rate constant k and shortened crystallization half time t_1/2. Furthermore, the crystallization rate of PLA is promoted with the incorporation of PBT with a large specific surface area. The average Avrami index n of all samples lies within the range of 3.3 ? 4.0, suggesting that morphologies of PBT do not affect the nucleation mechanism; however, the depression of equilibrium melting temperature in the blends ascribes the reductions of perfectness and size of the PLA crystallites. Besides, the nucleation of PLA crystallites around PBT fibers is probably faster than those around PBT spheres because the PBT chains oriented at the fiber surface as a result of flow‐induced crystallization during melt stretching may serve as the primary nuclei for PLA chains to drastically crystallize at the fiber surface. POLYM. ENG. SCI., 56:258–268, 2016. © 2015 Society of Plastics Engineers     

Solid‐state mechanical properties of polypropylene/nylon 6/clay nanocomposites

The mechanical and thermomechanical properties as well as microstructures of polypropylene/nylon 6/clay nanocomposites prepared by varying the loading of PP‐MA compatibilizer and organoclay (OMMT) were investigated. The compatibilizer PP‐MA was used to improve the adhesion between the phases of polymers and the dispersion of OMMT in polymer matrix. Improvement of interfacial adhesion between the PP and PA6 phases occurred after the addition of PP‐MA as confirmed by SEM micrographs. Moreover, as shown by the DSC thermograms and XRD results, the degree of crystallinity of PA6 decreased in the presence of PP‐MA. The presence of OMMT increased the tensile modulus as a function of OMMT loading due to the good dispersion of OMMT in the matrix. The insertion of polymer chains between clay platelets was verified by both XRD and TEM techniques. The viscosity of the nanocomposites decreased as PP‐MA loading increased due to the change in sizes of PA6 dispersed phase, and the viscosity increased as OMMT loading increased due to the interaction between the clay platelets and polymer chains. The clay platelets were located at the interface between PP and PA6 as confirmed by both SEM and TEM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electrical conductivity enhancement of spin‐coated PEDOT:PSS thin film via dipping method in low concentration aqueous DMSO

The electrical conductivity of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was enhanced by dipping the thin films prepared by spin coating technique in an aqueous DMSO solution. The low concentration range of DMSO in water between 0–5 vol % was studied in comparison with pure water and pure DMSO. It was found that the electrical conductivity dramatically increased as increasing the concentration of DMSO and reached the constant value of 350 S cm^?1 at 2 vol % of aqueous DMSO solution. This could be explained by the conformational change of PEDOT chains from the coil structure to the linear or expanded coil structure as confirmed by Raman spectra. Further, white patches were obviously noticed on the surface of the films dipped in pure DMSO, indicating the phase separation of conductive PEDOT grains and associated PSS. The sulfur element of the dipped film surface was investigated by XPS. The XPS S2p core‐level spectra displayed that the unassociated PSS was considerably removed from the surface of PEDOT:PSS films dipped in pure water and 2 vol % of aqueous DMSO solution, indicating that the presence of water in the solvents is important to prominently promote the washing effect. Finally, UV–Vis spectra revealed the improved transparency of the films probably owing to the decreased film thickness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42108.     

Synthesis and characterization of organic/inorganic epoxy nanocomposites from poly(aminopropyl/phenyl)silsesquioxanes

Organic/inorganic epoxy nanocomposites containing diglycidyl ether of bisphenol A (DGEBA), 4‐methylhexahydrophthalic anhydride (MHHPA) and poly(aminopropyl/phenyl) silsesquioxanes (PAPPS) were prepared and characterized. PAPPS were synthesized via fluoride‐catalyzed cage formation from random‐structured poly(phenyl)silsesquioxane (PPS) and 3‐aminopropyltriethoxysilane (APTES) in tetrahydrofuran (THF) using tetrabutylammonium fluoride (TBAF) catalyst containing substantial water. The PPS/APTES stoichiometric ratios were varied. The FTIR, ¹H, solid‐state 29 Si‐NMR studies show that PAPPS probably consists of cages, partial cages, and some linear structures containing phenyl and aminopropyl functional groups. The amine content was determined by back titration and elemental analysis. In comparison with neat epoxy, incorporation of these materials can improve the resultant thermal stabilities, raise glass transition temperatures (T_gs), and reduce coefficients of thermal expansion (CTEs) of epoxy nanocomposites as confirmed by TG/DTA, DMA and TMA tests, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of sulfenamide accelerators on cure kinetics and properties of natural rubber foam

The effect of types of sulfenamide accelerator, i.e., 2‐morpholinothiobenzotiazole (MBS), N‐t‐butylbenzothiazole‐2‐sulfenamide (TBBS), and N‐cyclohexyl benzothiazole‐2‐sulfenamide (CBS) on the cure kinetics and properties of natural rubber foam was studied. It has been found that the natural rubber compound with CBS accelerator shows the fastest sulfur vulcanization rate and the lowest activation energy (E_a) because CBS accelerator produces higher level of basicity of amine species than other sulfenamide accelerators, further forming a complex structure with zinc ion as ligand in sulfur vulcanization. Because of the fastest cure rate of CBS accelerator, natural rubber foam with CBS accelerator shows the smallest bubble size and narrowest bubble size distribution. Moreover, it exhibits the lowest cell density, thermal conductivity and thermal expansion coefficient, as well as the highest compression set as a result of fast crosslink reaction. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44822.     

Improvements in morphology,mechanical and thermal properties of films produced by reactive blending of poly(lactic acid)/natural rubber latex with dicumyl peroxide

The effect of dicumyl peroxide (DCP) as a free-radical cross-linking agent on the morphology, thermal and mechanical properties, and gas permeation of blown films prepared by reactive blending of poly(lactic acid) (PLA) and natural rubber latex was investigated. In comparison to the blown films without DCP, SEM micrographs revealed that the amount of debonded rubber domains from the cryofractured surface reduced considerably. This was when DCP at 0.003 phr was incorporated and the free radicals from thermally decomposed DCP reacted with PLA and NR chains, generating PLA–NR copolymers and cross-linked NR as confirmed by FTIR spectra. These PLA–NR copolymers acted as compatibilizers, which increased the strength at the PLA/NR interfaces, leading to the improvement in tensile strength, elongation at break, tensile toughness, impact strength, and tear strength. Although DCP did not influence the cold crystallization of PLA, TGA thermograms showed that thermal stability slightly increased owing to the enhanced interfacial adhesion. However, the addition of DCP at 0.005 and 0.010 phr resulted in a high content of cross-linked NR gel, by consuming the free radicals instead in copolymer formation. Therefore, the compatibilization efficiency was significantly reduced and the mechanical properties of reactive PLA/NR blown films finally dropped. Also, this poor interfacial adhesion facilitated the microvoid formation at the polymer–rubber interface as a result of mechanical stretching upon the film blowing process, increasing the permeation of water vapor and oxygen molecules. According to our study, it can be summarized that to optimize the morphology, mechanical properties, and gas permeation property of the free radical-assisted reactive blends, it is of great concern to carefully balance reactive compatibilizer formation and gel formation by adjusting the DCP content.     

Influence of diaminobenzoyl‐functionalized multiwalled carbon nanotubes on the nonisothermal curing kinetics,dynamic mechanical properties,and thermal conductivity of epoxy–anhydride composites

To obtain advanced materials with a high thermal dissipation, the addition of multiwalled carbon nanotubes containing diverse functionality groups, that is, as‐received multiwalled carbon nanotubes (AS‐MWCNTs) and diaminobenzoyl multiwalled carbon nanotubes (DA‐MWCNTs), to epoxy–anhydride composites was accomplished. According to nonisothermal differential scanning calorimetry analysis, the reactive functional groups present on the surfaces of the AS‐MWCNTs and DA‐MWCNTs accelerated the nucleophilic addition reaction of epoxy composites. Because of the difference in the reactivities of these functional groups toward epoxy groups, the distinction of fractional conversion and the reaction rate of the curing process were remarkably evident at the early stage. A suitable kinetic model was effectively elucidated with the Málek approach. The curing kinetics could best be described by a two‐parameter autocatalytic model as a truncated ?esták–Berggren model. The DA‐MWCNTs achieved effective load transfer and active heat conductive pathways; this resulted in good dynamic mechanical and thermal properties. As a result, the diglycidyl ether of bisphenol A/DA‐MWCNTs constituted an effective system with enhanced heat dissipation of materials for electronic applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43567.