Sayant Saengsuwan

Thermotropic liquid crystalline polymer (Rodrun LC5000)/polypropylene in situ composite films: rheology, morphology, molecular orientation and tensile properties

In situ composite films were prepared by a two-step method. First, polypropylene and thermotropic liquid crystalline polymer (TLCP), Rodrun LC5000 (80 mol% p-hydroxy benzoic acid (HBA)/20 mol% polyethylene terephthalate (PET)), were melt blended in a twin-screw extruder and then fabricated by extrusion through a mini-extruder as cast film. Rheological behavior of the blends, morphology of the extruded strands and films, and tensile properties of the in situ composite films were investigated. Rheological behavior of the blends at 295 8C studied using a plate-and-plate rheometer revealed a substantial reduction of the complex viscosity with increasing TLCP content, and all specimens exhibited shear thinning behavior. Over the angular frequency range of 0.6‐ 200 rad/s, the viscosity ratio (dispersed phase to matrix phase) was found to be very low, in the range of 0.03‐ 0.07. Morphologies of the fracture surfaces of the blend extrudates and the film surfaces etched in permanganic solution were investigated by scanning electron microscope (SEM). The TLCP droplets in the extruded strands were seen with a progressive deformation into fibrillar structure when TLCP content was increased up to 30 wt%. In the extruded films, TLCP fibrils with increasing aspect ratio (length to width) were observed with increasing TLCP concentration. Orientation functions of each component were determined by X-ray diffraction using a novel separation technique. It was observed that the Young’s modulus in machine direction of the extruded film was greatly improved with increasing TLCP loading, due to the increase in fiber aspect ratio and also molecular orientation. q 2003 Elsevier Science Ltd. All rights reserved.

Determination of orientation parameters in drawn films of thermotropic liquid crystalline polymer/polypropylene blends using WAXS

Abstract The effects of composition and compatibilizers on the molecular orientation in thermotropic liquid crystalline polymer (TLCP)/PP in situ composite films have been investigated using wide angle X-ray scattering (WAXS) techniques. The degree of preferred orientation for each component was evaluated using a novel separation technique based on a description of the scattering through spherical harmonic functions. The evaluated orientation parameters 〈P2〉 and 〈P4〉 of TLCP phase were found to increase up to 0.76 and 0.53, respectively, with increasing TLCP content and film draw ratio. In contrast, the PP component in all films exhibits a very low orientation (〈P2〉 ∼0.01) i.e. essentially isotropic. The PP component exhibits the so-called smectic phase which can be transformed to the more stable crystalline phase (α-form) by annealing at 110 °C for 2 h, with a small increase in the level of preferred orientation. The inclusion of particular polystyrene-based compatibilizers was observed to have a substantial effect on the modulus of the composite and in some cases this is reflected in the level of preferred orientation in the TLCP. We deduce that the orientation parameters are largely insensitive to the fibril morphology once a certain aspect ratio has been exceeded.

Rheology, morphology and tensile properties of thermotropic liquid crystalline polymer/polypropylene in-situ composites

Blends of various grades of polypropylene (PP) with a thermotropic liquid crystalline polymer (TLCP), namely a copolymer of p-benzoic acid and ethylene terephthalate (60/40 mole ratio) were prepared as extruded films. A thermoplastic elastomer styrene (ethylene-butylene) styrene (SEBS) was used as a compatibilizer. Melt viscosities of all specimens were measured using a plate-and-plate rheometer with oscillating mode in the shear rate region of 1 - 200 rad/s. Addition of SEBS compatibilizer resulted in an increase of the blend viscosity. Observation of the blend morphology revealed an improvement of TLCP dispersion. The TLCP fiber aspect ratio (length to diameter) in the extruded film also increased after addition of SEBS. As a result, the film modulus in extrusion direction was enhanced. The tensile strength of the film specimen was also increased due to an improvement of interfacial adhesion.

Multi-triphenylamine-substituted bis(thiophenyl)benzothiadiazoles as highly efficient solution-processed non-doped red light-emitters for OLEDs

New di- and penta(triphenylamine)-substituted bis(thiophenyl)benzothiadiazoles, namely T2B and T5B, respectively, were synthesized and characterized. T5B showed an outstanding red emission with high Tg amorphous and good film-forming properties and excellent potential as a solution-processed non-doped red light-emitter for OLEDs. A simple structured red OLED (ITO/PEDOT:PSS/T5B(spin coating)/BCP/LiF:Al) with a high efficiency (6.25 cd A−1 at 4.1 mA cm−2) and a pure red emission (CIE = 0.67, 0.33) was attained.

Synthesis and properties of biodegradable hydrogels based on cross-linked natural rubber and cassava starch:

A series of interpenetrating polymer network (IPN) hydrogels based on cross-linked natural rubber (XNR) and cassava starch (CSt) as biodegradable membrane material were synthesized via free radical polymerization in latex state using N,N′-methylenebisacrylamide (MBA) and maleic acid as cross-linkers. The IPN XNR/CSt hydrogels were confirmed and characterized by infrared spectroscopy, thermal analysis, and X-ray diffraction. The results showed that with increasing MBA content from 1.0 to 2.5 phr, cross-link density and gel fraction of XNR increased from 0.80 to 0.90 mol M−3 and from 19.7% to 30.5%, respectively. The gel fraction and tensile strength of the IPN XNR/CSt hydrogels also gradually increased as a function of MBA content but the water swelling and elongation at break decreased slightly. The IPN XNR/CSt containing 1.0 phr MBA displayed the highest water swelling of 82%. The weight retentions of IPN XNR/CSt hydrogels after soil degradations for 90 days increased from 48% to 56% with increasing MBA from 1.0 phr to 2.5 phr. The IPN XNR/CSt exhibited not only a good biodegradation but also high mechanical strength and flexibility. Also, the IPN XNR/CSt could be a promising candidate as a biodegradable membrane for longer released fertilizer application.

Synthesis, physical and electroluminescence properties of 3,6-dipyrenylcarbazole end capped oligofluorenes

A series of oligofluorenes bearing two 3,6-dipyrenylcarbazole units as the terminal substituents, namely BPCFn (n = 1–3), were successfully synthesized and characterized as non-doped hole-transporting blue emitters. These molecules showed strong blue emission with good solubility, and thermally stable amorphous and excellent film-forming properties. OLEDs using these materials as the emissive layers were fabricated by a simple solution spin-coating process. The blue OLED with excellent device performance (brightness of 6085 cd m−2, luminance efficiency of 4.13 cd A−1 and turn-on voltage of 3.4 V) was attained from BPCF3.

correlations of mechanical properties and microstructural parameters in annealed drawn film of liquid crystalline polymer in situ reinforced PP

Abstract Drawn composite thin film based on thermotropic liquid crystalline polymer (TLCP) and polypropylene (PP) was annealed at 130 °C at different times. The influence of annealing time on microstructural and mechanical properties of the composite film has been studied. The correlation in mechanical properties and their microstructural parameters has also been investigated. X-Ray diffraction results reveal that the smectic mesophase transforms progressively into the monoclinic phase as annealing time is increased. Consequently, the true crystallinity (Xc), crystal thickness (L) as well as relative level of molecular orientation of PP crystalline phase in the annealed TLCP/PP films are increased significantly. Also, the TLCP fibrils have no influence on the microstructure of PP crystalline phase. The apparent crystallinity (Xc,a) of PP phase evaluated by DSC also increase significantly with annealing time. As a result, the increases of these microstructural parameters coupled with the reinforcement of TLCP fibrils could be contributed directly to the remarkable enhancement of mechanical properties of the annealed TLCP/PP film in both machine (MD) and transverse (TD) directions. The correlation of moduli with microstructural parameters (Xc, Xc,a and L) exhibits nonlinear relations. However, the relative level of molecular orientation is a more suitable parameter to correlate with the improvement of mechanical properties of the annealed TLCP/PP film. Finally, this work presents that the mechanical properties of the TLCP in situ reinforced thermoplastics can be significantly enhanced via a simple thermal treatment.

Influence of annealing on microstructure & molecular orientation, thermal behaviour, mechanical properties and their correlations of uniaxially drawn iPP thin film

Abstract The influence of annealing on the microstructure and molecular orientation, thermal behaviour and mechanical properties of uniaxially drawn iPP thin film was studied by wide-angle X-ray diffraction, differential scanning calorimetry and tensile testing, respectively. The correlations of mechanical and microstructural properties of annealed films were also examined. The transformation of smectic phase of iPP to the α-form was more pronounced with increasing annealing time and temperature. The true and apparent crystallinities and crystal thickness were strongly enhanced with annealing time and temperature. The relative molecular orientation tended to increase with annealing time. These results caused the significant improvement of modulus and tensile strength of the annealed films in both machine (MD) and transverse (TD) directions. The increases in MD-Young’s modulus and MD-tensile strength were well correlated with the increase in true crystallinity obtained in equatorial scans. Some relationship between the increase in crystal thickness and the increase in Young’s modulus in both MD and TD directions was also found.

Atomic force microscopy investigation of phase morphology correlated with adhesive properties for modified telechelic natural rubber based-pressure sensitive adhesive

Abstract Atomic force microscopy (AFM) is a powerful technique to determine phase morphology and surface mechanical properties of materials. In this research natural rubber was degraded and grafted by malelic anhydride before modification with 3-amino-1,2,4-triazole to obtain modified telechelic natural rubber or modified TNR. It was then blended with cumarone-indene resin at 10, 30, and 50 phr, acting as tackifier. Phase morphology and surface topography were investigated by intermitted AFM. The results showed that tackifier enriched domains were clearly observed in modified TNR matrix after added 30 and 50 phr and the domain sizes were approximately to be the order of micrometer (5–10 µm) which it increased with increasing tackifier content. The intermolecular hydrogen bonding interaction between tackifier and modified TNR was observed by attenuated total reflectance Fourier transform infrared spectroscopy. The adhesive properties (loop tack, peel, and shear strength) were governed by the size of tackifier enriched domains, surface mean roughness and compatibility or interaction between modified TNR rubber and cumarone-indene tackifier resin.

Thermal and Mechanical Properties of Mulch Film from Poly(Lactic Acid)/Expoxidized Natural Rubber Blends Filled with Rutile TiO2 as Fillers

The aim of this research was to reduce and improve the brittleness and thermal properties of poly lactic acid (PLA), respectively. Epoxidized natural rubber (ENR) was used to enhance the toughness and rutile titanium dioxide (R-TiO2) as filler was also incorporated to improve the thermal properties of the PLA. 10wt% ENR with epoxidation contents of 25 mol% (ENR25) and 50 mol% (ENR50) and various R-TiO2 contents (0-10 phr)were compounded with PLA by using a twin-screw extruder at 155-165°C and a rotor speed of 40 rpm. The pellets of blends were then formed a thin film using a cast film extruder machine and cooled down under air flow. Thermal and mechanical properties and morphology of PLA/ENR/R-TiO2 thin film were investigated. The crystallinity of PLA was found to increase with addition of ENR. The mechanical properties of thin film showed that the ENR50 enhanced the elongation but reduced the tensile strength of PLA with addition of R-TiO2 at 5 and 10 phr, respectively. The TGA indicated that the addition of 10 phr R-TiO2 increased in the decomposition temperature at 5% weight loss (Td5%) of PLA/ENR film. Thus the thermal stability of PLA/ENR50 was found to improve with addition of R-TiO2. From morphology study, the ENR50 phase showed a good dispersion in the PLA matrix. In conclusion, the addition of ENR and R-TiO2 was found to enhance both toughness and thermal stability of PLA.