Fiber–matrix interactions in aramid‐short‐fiber‐reinforced thermoplastic polyurethane composites

The mechanical and dynamic mechanical properties of thermoplastic polyurethane (TPU) elastomers reinforced with two types of aramid short fibers, m‐aramid (Teijin‐Conex) and copoly(p‐aramid) (Technora), were investigated in this study with respect to the fiber loading. In general, both types of composites exhibited very similar stress–strain behaviors, except that Technora–TPU was stronger than Conex–TPU. This was primarily due to the intrinsic strength of the reinforcing fibers. Both types of fibers reinforced TPU effectively without any surface treatment. This could be attributed to good fiber–matrix interactions, which were revealed by the broadening of the tan δ peak in dynamic mechanical analysis. Furthermore, the morphologies of cryogenically fractured surfaces of the composites and extracted fibers, investigated with scanning electron microscopy, revealed possible polar–polar interactions between the aramid fibers and TPU matrices. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1059–1067, 2003     

Isothermal decomposition behavior and dynamic mechanical properties of in situ‐reinforcing elastomer composites based on thermoplastic elastomers and thermotropic liquid crystalline polymer

In situ‐reinforcing composites based on two elastomer matrices very different in melt viscosity, styrene–(ethylene butylene)–styrene triblock copolymer (Kraton G1650), and styrene–(ethylene propylene) diblock copolymer (Kraton G1701), and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a twin‐screw extruder. The isothermal decomposition behavior and dynamic mechanical properties of the extruded strands were investigated by means of thermogravimetry (TG) and dynamic mechanical analysis (DMA), respectively. No significant change in the shape of TG curves for the neat matrices and their LC3000‐containing blends was observed under isothermal heating in nitrogen. In air, G1650 and G1701 showed a single weight‐loss stage and rapid decomposition whereas their blends with 30 wt % LC3000 showed different profiles of weight loss depending on isothermal temperatures. The calculated kinetic parameters indicated that the thermal stability of the polymers is much higher in nitrogen than in air and suggested an enhancement of thermal resistance of the elastomer matrices by addition of TLCP. DMA results showed a great enhancement in dynamic moduli for the blend with 10 wt % LC3000 when compared with the neat matrix. The tan δ peaks corresponding to the elastic and hard phases in both matrices mostly shifted to the lower temperature with LC3000 loading. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 917–927, 2007     

Polyethylene composite fibers. I. Composite fibers of high‐density polyethylene

Polymer matrix composites are generally studied in the form of bulk solids, and very few works have examined composite fibers. The research described here extended such bulk studies to fibers. The question is whether or not what has been reported for bulk polymers will be the same in fibers. In this article are reported studies of high‐density polyethylene (HDPE), whereas those of linear low‐density polyethylene are reported in part II of this article series. Two types of filler were used, that is, organically modified montmorillonite (OMMT), in which the nanosized filler particles had a high aspect ratio, and microsized calcium carbonate (CaCO₃), with an aspect ratio nearer to unity. Composite fibers of both as‐spun and highly drawn forms were prepared, and their structures, morphology, and mechanical properties were studied. It was found that the microsized particles gave HDPE composite fibers with mechanical properties that were the same as those of the neat polymer. In the case of clay composite fibers, the clay interfered with the yield process, and the usual yield point could not be observed. The particle shape did not affect the mechanical properties. The fibers showed different deformation morphologies at low draw ratios. The CaCO₃ composite fibers showed cavities, which were indicative of low interaction between the polymer and the filler. The OMMT composite fibers showed platelets aligned along the fibers and good polymer–filler interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermo‐oxidative decomposition kinetics of elastomeric composites based on styrene‐(ethylene‐butylene)‐styrene triblock copolymer and organomontmorillonite

The elastomeric nanocomposites based on organomontmorillonite (OMMT) and styrene‐(ethylene‐butylene)‐styrene (SEBS) thermoplastic elastomer were prepared by melt processing using maleic anhydride grafted SEBS (SEBS‐g‐MA) as compatibilizer. Thermo‐oxidative decomposition behavior of the neat components and the nanocomposites were investigated using thermogravimertic analysis (TGA) in air atmosphere. The isoconversional method is employed to study the kinetics of thermo‐oxidative degradation. The heating modes and the composition of nanocomposites were found to affect the kinetic parameters (E_a, lnA and n). The E_a and lnA values of SEBS, OMMT, and their composites are much higher under dynamic heating than under isothermal heating. The reaction order (n) of OMMT was lower than those of SEBS and their composites. The obtained TG profiles and calculated kinetic parameters indicated that the incorporation of OMMT into SEBS significantly improved the thermal stability both under dynamic heating and under isothermal heating. The simultaneously obtained DSC data showed that the enthalpy of thermal decomposition decreased with OMMT loading. No significant change in the nonisothermal and isothermal stability of the nanocomposites with addition of SEBS‐g‐MA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of compatibilizer on notched impact strength and fractography of HDPE–organoclay composites

The focus of this study was the notched impact property of high‐density polyethylene (HDPE)–organoclay composites and the resultant morphology of impact‐fractured surfaces. Composites with a different organoclay content and degree of organoclay dispersion were compared with neat HDPE under identical conditions. The degree of organoclay dispersion was controlled through the use of a compatibilizer, maleic anhydride grafted polyethylene. It was found that the addition of organoclay can slightly increase the elastic modulus and notched impact strength of the composite. When the level of organoclay dispersion was improved by using compatibilizer, elastic modulus and toughness further increased. A significant increase in yield strength was also notable. The presence of organoclay was found to suppress strain hardening of the matrix during tensile testing. The impact‐fractured surfaces of failed specimens were studied with scanning electron microscopy. The micromechanism for the increased toughness of HDPE–organoclay composites was discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Origin of phase shift in atomic force microscopic investigation of the surface morphology of NR/NBR blend film

Atomic force microscopy (AFM) was used to study the morphology and surface properties of NR/NBR blend. Blends at 1/3, 1/1 and 3/1 weight ratios were prepared in benzene and formed film by casting. AFM phase images of these blends in tapping mode displayed islands in the sea morphology or matrix-dispersed structures. For blend 1/3, NR formed dispersed phase while in blends 1/1 and 3/1 phase inversion was observed. NR showed higher phase shift angle in AFM phase imaging for all blends. This circumstance was governed by adhesion energy hysteresis between the device tip and the rubber surface rather than surface stiffness of the materials, as proved by force distance measurements in the AFM contact mode.     

On morphologies developed during two‐dimensional compaction of woven polypropylene tapes

The microstructure of compacted woven polypropylene cloths prepared at their optimum compaction temperature of 184°C has been examined. Details of transverse and longitudinal cross‐sections have been revealed by permanganic etching and observed with scanning electron microscopy. The original cloth was found to contain perpendicular cracks and biconical defects reported previously in other systems. After compaction, the cloth bonded together to form a thick solid sheet, with a melting point raised for the residual material but reduced for the recrystallized component. The higher melting regions form a continuous three‐dimensional network with linear traces in a longitudinal section, in agreement with recent observations of fiber structure. Recrystallization occurs both within and externally from tapes: where parallel tapes meet, transcrystalline layers emanate from tape surfaces, with a distinct line where the two growth fronts meet. In some more extensive recrystallized regions row structures are formed, probably indicating local flow during compaction. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 787–793, 2000     

Effect of LCP and rPET as reinforcing materials on rheology,morphology, and thermal properties of in situ microfibrillar‐reinforced elastomer composites

Microfibrillar‐reinforced elastomer composites based on two dispersed phases, liquid crystalline polymer (LCP) and recycled poly(ethylene terephthalate)(rPET), and styrene‐(ethylene butylene)‐styrene (SEBS) were prepared using extrusion process. The rheological behavior, morphology, and thermal stability of SEBS/LCP and SEBS/rPET blends containing various dispersed phase contents were investigated. All blends and LCP exhibited shear thinning behavior, whereas Newtonian fluid behavior was observed for rPET. The incorporation of both LCP and rPET into SEBS significantly improved the processability by bringing down the melt viscosity of the blend system. The fibrillation of LCP dispersed phase was clearly observed in as‐extruded strand with addition of LCP up to 20–30 wt %. Although the viscosity ratio of SEBS/rPET system is very low (0.03), rPET domains mostly appeared as droplets in as‐extruded strand. The results obtained from thermogravimetric analysis suggested that an addition of LCP and rPET into the elastomer matrix improved the thermal resistance significantly in air but not in nitrogen. The simultaneous DSC profiles revealed that the thermal degradation of all polymers examined were endothermic and exothermic in nitrogen and in air, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Liquid crystalline copolyester/polyethylene in situ composite film: Rheology,morphology, molecular orientation,and tensile properties

A thermotropic liquid crystalline copolyester (TLCP) was blended with low density polyethylene using a corotating twin screw extruder and then fabricated by extrusion through a miniextruder as cast film. Rheological behavior, morphology, and tensile properties of the blends were investigated. Melt viscosities of neat components and blends measured by using plate‐and‐plate and capillary rheometers at 240°C, in the shear rate range 1–10⁴ s^?1, showed similar shear thinning effect. The viscosity values measured by the two techniques in the overlapping range of shear rate are found to be identical, which is in accord with the Cox–Merz rule. Addition of TLCP slightly reduces the matrix melt viscosity. TLCP dispersed phase in the extruded strand appeared in the form of spherical droplets. These droplets were elongated into fibrils with high aspect ratio (length to width) at the film extrusion step. As a result, the Young's modulus in machine direction (MD) of the composite film was greatly enhanced. At 20 wt % of TLCP, the MD Young's modulus was found to be about 16‐fold increase compared to that of the neat polyethylene film. However, the elongation at break sharply dropped with the increase of TLCP content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 561–567, 2002; DOI 10.1002/app.10307