Morphology,thermal, and dynamic mechanical properties of poly(lactic acid)/sisal whisker nanocomposites

Sisal whiskers were used as biobased nanofillers to prepare poly(lactic acid) (PLA)‐based nanocomposites. The whiskers were prepared from sisal fibers via sulfuric acid hydrolysis. Freeze drying of the aqueous whisker suspension was carried out to obtain loosely packed dry sisal whiskers. The nanocomposites were prepared by melt mixing, followed by hot melt pressing. The effect of the freeze drying of the nanofibers, the treatments of the samples with maleic anhydride (MA)/dicumyl peroxide (DCP) and with DCP, and the premixing of the powdered components on the dispersion of the whiskers in the PLA matrix and on the morphology, as well as the thermal and dynamic mechanical properties, of the resultant nanocomposites were investigated. Transmission electron microscopy micrographs show that the acid hydrolysis has led to separation of the whiskers, which had an approximate length and diameter of 195 and 15 nm, respectively. The TEM images of the nanocomposites show similar dispersion of the whiskers in the PLA matrix, whether untreated or MA/DCP or DCP treated. It was found that the crystallization behavior of the PLA matrix changed somewhat depending on whether the samples were treated or not. The thermogravimetric analysis results show a slight decrease in the thermal stabilities of the untreated and the MA/DCP‐treated nanocomposite samples compared to that of the neat PLA, whereas the DCP treatment slightly improved the thermal stability of the nanocomposites. The storage modulus of the nanocomposites increased over the investigated temperature region, and the incorporation of sisal whiskers reduced the intensity of the glass transition at 67°C. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Thermal and mechanical properties of poly(ethylene terephthalate)/lamellar zirconium phosphate nanocomposites

The preparation of nanocomposites of poly (ethylene terephthalate) (PET) and lamellar zirconium phosphorous compounds by melt extrusion was investigated. Two types of zirconium phosphorous compounds were synthesized by the direct precipitation reaction method: α‐zirconium bis(monohydrogen orthophosphate) monohydrate (ZrP) and organic–inorganic hybrid layered zirconium phenylphosphonate (ZrPP). Composites containing 2 and 5 wt % ZrP and ZrPP were prepared in a twin‐screw extruder and specimens were obtained by injection molding. The extent of dispersion of the layered filler in the composite matrix was investigated by X‐ray diffraction and transmission electron microscopy (TEM). The crystallization and thermal properties were analyzed by differential scanning calorimetry and thermogravimetry, and the mechanical properties were evaluated by tensile tests. Whereas ZrP‐containing composites showe characteristic diffraction peaks at 2θ 11.7° (d = 7.54 Å), indicative of no delamination, ZrPP showed practically no low‐angle diffraction peak at 2θ 5.5° (d = 15.24 Å), indicating loss of the layered order. TEM images of ZrPP particles indicated the formation of an intercalated/partially delaminated nanocomposite. The behavior was attributed to the higher affinity of the polyester with phenyl groups on the platelet surface of ZrPP. In both cases, the addition of the fillers increased the crystallization rate and the modulus. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3868–3876, 2006     

Layer‐structured poly(vinyl alcohol)/graphene oxide nanocomposites with improved thermal and mechanical properties

Layer‐structured poly(vinyl alcohol)/graphene oxide nanocomposites in the form of films are prepared by simple solution processing. The structure and properties of these nanocomposites are studied using X‐ray diffractions, scanning electron microscopy, Fourier‐transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The results indicate that graphene oxide is dispersed on a molecular scale and aligned in the poly(vinyl alcohol) matrix, and there exists strong interfacial interactions between both components, which are responsible for the significant improvement in the thermal and mechanical properties of the nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and mechanical properties of poly(butylene terephthalate)/epoxy blends

In this study, melt blends of poly(butylene terephthalate) (PBT) with epoxy resin were characterized by dynamic mechanical analysis, differential scanning calorimetry, tensile testing, Fourier transform infrared spectroscopy, and wide‐angle X‐ray diffraction. The results indicate that the presence of epoxy resin influenced either the mechanical properties of the PBT/epoxy blends or the crystallization of PBT. The epoxy resin was completely miscible with the PBT matrix. This was beneficial to the improvement of the impact performance of the PBT/epoxy blends. The modification of the PBT/epoxy blends were achieved at epoxy resin contents from 1 to 7%. The maximum increase of the notched Izod impact strength (≈ 20%) of the PBT/epoxy blends was obtained at 1 wt % epoxy resin content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Extremely oriented tunicin whiskers in poly(vinyl alcohol) nanocomposites

In order to utilize the excellent mechanical properties of cellulose whiskers (CWs) along their length, the present work was undertaken to embed CWs with highly oriented forms in a polymer matrix. Nanocomposite fibers were prepared using poly(vinyl alcohol) (PVA; degree of polymerization of 1500) as the matrix and a stable aqueous suspension of CWs extracted from tunicates as the reinforcing phase. Macroscopically homogeneous suspensions of PVA–CW were gel‐spun in a methanol coagulating bath. The as‐spun fibers included CWs oriented along the fiber axis and showed a significant increase in dynamic storage modulus. Hot drawing of the PVA–CW as‐spun fibers to their maximal draw ratio led to extremely high orientation of the CWs together with a drastic reduction in voids in the fiber matrix. Outstanding mechanical properties of the drawn composites were obtained by the incorporation of only a small amount (1 wt% of solid PVA content) of CWs. The stress transfer mechanism in the fibers was studied using an X‐ray diffraction technique by applying stress to the whole composite with in situ monitoring of stress on the incorporated CWs. The applied external stress was found to be translated efficiently to the incorporated CWs through the PVA matrix, suggesting strong interfacial bonding between filler and matrix. The strong interaction and efficient stress transfer between matrix and filler are suggested as the cause for the observed improvements in mechanical properties of the composites. Copyright © 2011 Society of Chemical Industry     

Nonisothermal crystallization behavior and mechanical properties of poly(butylene succinate)/silica nanocomposites

Silica nanoparticles and poly(butylene succinate) (PBS) nanocomposites were prepared by a melt‐blending process. The influence of silica nanoparticles on the nonisothermal crystallization behavior, crystal structure, and mechanical properties of the PBS/silica nanocomposites was investigated. The crystallization peak temperature of the PBS/silica nanocomposites was higher than that of neat PBS at various cooling rates. The half‐time of crystallization decreased with increasing silica loading; this indicated the nucleating role of silica nanoparticles. The nonisothermal crystallization data were analyzed by the Ozawa, Avrami, and Mo methods. The validity of kinetics models on the nonisothermal crystallization process of the PBS/silica nanocomposites is discussed. The approach developed by Mo successfully described the nonisothermal crystallization process of the PBS and its nanocomposites. A study of the nucleation activity revealed that the silica nanoparticles had a good nucleation effect on PBS. The crystallization activation energy calculated by Kissinger's method increased with increasing silica content. The modulus and yield strength were enhanced with the addition of silica nanoparticles into the PBS matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation, characterization and pyrolysis of poly(furfuryl alcohol)/porous silica glass nanocomposites: novel route to carbon template

In this paper we report the preparation of glassy carbon through the pyrolysis of poly(furfuryl alcohol) inside the pores of Vycor glass, which was used as a template. Different routes to the in situ polymerization of furfuryl alcohol inside the pores of Vycor glass were developed. The nanocomposites glass/polymer obtained were characterized by several techniques. Carbonization of these nanocomposites produces new silica glass/carbon nanocomposites, which were characterized and treated with HF to remove the silica fraction. It was found that the resulting carbon presents low crystallinity when compared to graphite. However, it presents more order than the glassy carbon resulting from the pyrolysis of the free poly(furfuryl alcohol) resin.     

Thermal and dynamic mechanical behavior of poly(vinyl chloride)/wood flour composites

Thermal and dynamic mechanical behaviors of wood plastic composites made of poly vinyl chloride (PVC) and surface treated, untreated wood flour were characterized by using differential scanning calorimetry and dynamic mechanical analysis. Glass transition temperature (T_g) of PVC was slightly increased by the addition of wood flour and by wood flour surface treatments. Heat capacity differences (ΔC_p) of composites before and after glass transition were markedly reduced. PVC/wood composites exhibited smaller tan δ peaks than PVC alone, suggesting that less energy was dissipated for coordinated movements and disentanglements of PVC polymer chains in the composites. The rubbery plateaus of storage modulus (E′) curves almost disappeared for PVC/wood composites in contrast to a well defined plateau range for pure PVC. It is proposed that wood flour particles act as “physical crosslinking points” or “pinning centers” inside the PVC matrix, resulting in the absence of the rubbery plateau and high E′ above T_g. The mobility of PVC chain segments were further retarded by the presence of surface modified wood flour. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interrelationship of thermal and mechanical properties of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate)/graphene nanocomposites

In the present work, attempts were made to investigate the thermal and mechanical properties of melt‐processed poly(ethylene terephthalate) (PET)/poly(ethylene 2,6‐naphthalate) (PEN) blends and its nanocomposites containing graphene by using differential scanning calorimetry and tensile test experimenting. The results showed that crystallinity, which depends on a blend ratio, completely disappeared in a composition of 50/50. By introducing graphene to PET, even in low concentrations, the crystallinity of samples increased, while the nanocomposite of PEN indicated reverse behavior, and the crystallinity was reduced by adding graphene. In the case of PET‐rich (75/25) nanocomposite blends, by increasing the nano content in the blend, the crystallinity of the samples was enhanced. This behavior was attributed to the nucleating effect of graphene particles in the samples. From the results of mechanical experiments, it was found in PET‐rich blends that by increasing the PEN/PET ratio, the modulus of samples decreased, whereas in the case of PEN‐rich blends, a slight increment of modulus is seen as a result of the increment of the PEN/PET ratio. The two contradicting behaviors were attributed to the reduction of crystallinity of PET‐rich blends by enhancement of PEN/PET ratio and the rigid structure of PEN chains in PEN‐rich blends. Unlike the different modulus change of PET‐rich and PEN‐rich blends, the nanocomposites of these blends similarly indicated an increment of modulus and characteristics of rigid materials by increasing the nano content. Furthermore, the same behavior was detected in nanocomposites of each polymer (PET and PEN nanocomposites). The alteration from ductile to rigid conduction was related to the impedance in the role of graphene plates against the flexibility of polymer chains and high values of graphene modulus. J. VINYL ADDIT. TECHNOL., 23:210–218, 2017. © 2015 Society of Plastics Engineers     

The excellent gas barrier properties and unique mechanical properties of poly(propylene carbonate)/organo-montmorillonite nanocomposites

Intercalated nanocomposites comprised of poly(propylene carbonate) (PPC) and organo-montmorillonite (OMMT) were prepared via a direct melt blending method. The morphological, thermal, rheological, mechanical, and gas barrier properties of composites were carried out in detail. Results of XRD, TEM, and SEM revealed that OMMT dispersed homogeneously in the polymer matrix, and were intercalated by PPC macromolecules. Compared with neat PPC, the PPC/OMMT nanocomposites showed an enhancement in the 5 wt% weight loss temperature (T _?5%) by near 20 °C with 3 phr OMMT concentration. With the percolation threshold formed, the rheological properties of composites translated from a liquid-like behavior to a solid-like one. Interestingly, PPC/OMMT nanocomposites revealed a concurrent improvement in the modulus, yield strength, and toughness with the addition of homogeneously dispersed clay. The oxygen permeability of well-dispersed PPC/OMMT nanocomposites reduced significantly compared with that of neat PPC. Consequently, this convenient and effective method, which facilitates to prepare PPC/OMMT nanocomposites with superior mechanical properties and excellent gas barrier performances, can be considered to broaden the application of PPC.     

Thermal processability and properties of highly filled poly(vinyl alcohol)/talc composite

Abstract

A highly filled PVA/talc composite was prepared through our invented thermal processing technology without using any coupling agent or compatibiliser. The results showed that compared with neat PVA, the melt temperature of the composite decreased and the degradation temperature increased, providing a big temperature window for thermal processing of PVA/talc composite. The composite melt exhibited shear thinning behaviour while its viscosity increased with increasing talc, still satisfied the requirement of thermal processing. The morphology analysis confirmed that talc was well dispersed in PVA, improving heat deflection temperature (HDT), tensile strength and modulus of PVA. When talc was 50 wt-%, the HDT, tensile strength and modulus of the composite were 115°C, 48 MPa, 1·23 GPa respectively, increased by 92, 16 and 150%, compared with PVA, and the elongation at break was 100% of the composite, confirming that the high filled PVA/talc composite was a novel PVA based material with excellent thermal and mechanical properties.     

Recycled poly(ethylene terephthalate)/layered silicate nanocomposites: morphology and tensile mechanical properties

Various amounts (1, 3 and 5 wt%) of a non-modified natural montmorillonite clay (Cloisite^® Na⁺) or of an ion-exchanged clay modified with quaternary ammonium salt (Cloisite^® 25A) were dispersed in a recycled poly(ethylene terephthalate) matrix (rPET) by a melt intercalation process. Microphotographs of composite fracture surfaces bring evidence that particles of Cloisite^® 25A are much better dispersed in the rPET matrix than those of Cloisite^® Na⁺. Moreover, WAXS measurements indicate that the lamellar periodicity of Cloisite^® 25A is increased in the composites, which evidences intercalation of rPET between silicate layers (lamellae) of the clay. In the case of Cloisite^® Na⁺, a very small thickening of lamellae due to mixing with rPET indicates only minute intercalation.Uniaxial tensile tests show that both clays increase the modulus of the rPET composites; more effective Cloisite^® 25A accounts for a 30% increase at loading of 5 wt%. Yield strength remains practically unaffected by the used fractions of the clays while tensile strength slightly decreases with the clay content; in parallel, strain at break dramatically drops. Tensile compliance of the composites is virtually independent of applied stress up to 26 MPa. Essential part of the compliance corresponds to the elastic time-independent component, while the viscoelastic component is low corresponding only to a few percent of the compliance even at relatively high stresses. The compliance of the composites is only slightly lower than that of the neat rPET, the reinforcing effect of Cloisite^® 25A being somewhat stronger. Both clays have beneficial effect on the dimensional stability of the composites since—in contrast to the neat rPET—the creep rate does not rise at long creep periods.     

Preparation and properties of poly(ethylene terephthalate)/inorganic whiskers composites

To improve the crystallization and mechanical properties of poly(ethylene terephthalate) (PET), in this work, PET/SiO₂‐MgO‐CaO whiskers composites were prepared via in situ polymerization. The morphology, crystallization, and mechanical properties of the prepared composites were investigated. It was found that inorganic whiskers could be easily dispersed in PET matrix, as demonstrated by SEM and PLM. DSC and PLM observation indicated a strong nucleation capability of inorganic whiskers for PET. Mechanical analysis results showed that the glass transition temperature, tensile strength, and modulus of the composites were greatly improved. A possible chemical bonding between PET chains and the surface of whiskers was observed by FTIR, TGA, and sedimentation experiment. It could be the main reason for the good dispersion and improved properties of the prepared composites. This work is important for the application of PET due to the low cost but high reinforcing efficiency of this inorganic whisker. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal and mechanical properties of poly(ε‐caprolactone)/polyhedral oligomeric silsesquioxane nanocomposites

Poly(ε‐caprolactone) (PCL)/trisilanolphenyl polyhedral oligomeric silsesquioxane (TspPOSS) nanocomposites were prepared by solution mixing followed by film casting. Wide‐angle X‐ray diffraction and field‐emission scanning electron microscopy observations showed that the POSS molecules formed crystal domains and dispersed uniformly on the nanoscale in the PCL matrix. Fourier transform infrared analysis of the nanocomposites revealed that there are hydrogen‐bonded interactions between the silanol group of the TspPOSS and carbonyl oxygen of the PCL. Differential scanning calorimetry, tensile testing, and dynamic mechanical analysis (DMA) showed that, with increasing POSS content in the nanocomposites, the melting temperature and degree of crystallinity decreased while glass transition temperature, tensile modulus and strength increased without sacrificing the ductility of the PCL. DMA results also demonstrated the presence of a rubbery plateau above the melting temperature of the PCL/TspPOSS nanocomposites, and the moduli at the plateau region increased with increasing POSS content in the nanocomposites, implying that the PCL/TspPOSS nanocomposites formed a physically crosslinked structure. The physically crosslinked PCL/TspPOSS nanocomposites exhibited a thermally triggered shape memory effect. Copyright © 2012 Society of Chemical Industry     

Uniaxial drawing of poly(vinyl alcohol)/graphene oxide nanocomposites

The unique potential of graphene oxide (GO) was exploited in the nanocomposites by a simple uniaxial drawing (up to three times) of poly(vinyl alcohol) (PVA)/GO nanocomposites with a small amount loading of GO. From X-ray diffraction images, the PVA crystallites were found to be oriented parallel to the drawn direction. At the same time, exfoliated GO platelets were found to be aligned parallel to the film surface. Compared with the properties of the as-cast nanocomposites, those of the uniaxially drawn nanocomposites were found to be remarkably enhanced. For the mechanical properties, not only Young’s modulus and tensile strength but also the toughness of the nanocomposites increased by the uniaxial drawing. It was revealed that 260% increase in toughness was achieved for the drawn nanocomposite with 1% w/w GO loading. Significant suppression of the swelling in water resulted in the excellent barrier properties against water, which exceeded that of the conventional high-barrier polymer, such as poly(vinylidene chloride). We revealed that this simple, fast and environmentally friendly process of uniaxial drawing exploits the excellent properties and high aspect ratio of GO in the nanocomposites.     

Effect of vanadium pentoxide on the mechanical,thermal, and electrical properties of poly(vinyl alcohol)/vanadium pentoxide nanocomposites

In this study, we examined the effect of vanadium pentoxide (V₂O₅) on the mechanical, thermal, and morphological properties of poly(vinyl alcohol) (PVA)/V₂O₅ nanocomposites. The PVA/V₂O₅ nanocomposites were prepared by solution mixing, followed by film casting. The results show that the Young's moduli of the resulting nanocomposites films were higher than the pure PVA modulus with increasing V₂O₅ content, and it reached a maximum point at about 0.4 wt % V₂O₅ content at 8.55 GPa. The tensile strength and stress at break increased with increasing V₂O₅ content. The addition of V₂O₅ did not affect the melting temperature. The crystallization temperatures of PVA were significantly changed with increasing V₂O₅ content. The 5% weight loss degradation temperature of the nanocomposites was measured by thermogravimetric analysis. The degradation temperatures of the V₂O₅ nanocomposites increased with increasing filler content and were higher than the degradation temperature of pure PVA; this showed a lower thermal stability compared to those of the nanocomposites. The results show that the thermal stability increased with the incorporation of V₂O₅ nanoparticles. The dielectric constant of PVA had a tendency to improve when the dispersion of particles was effective. The morphology of the surfaces the nanocomposites was examined by scanning electron microscopy. We observed that the dispersion of the V₂O₅ nanoparticles was relatively good; only few aggregations existed after the addition of the V₂O₅ nanoparticles at greater than 0.4 wt %. In perspective, the addition of 0.4 wt % V₂O₅ nanoparticles into PVA maximized the mechanical, thermal, and electrical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of layer-aligned poly(vinyl alcohol)/graphene nanocomposites

Layer-aligned poly(vinyl alcohol)/graphene nanocomposites in the form of films are prepared by reducing graphite oxide in the polymer matrix in a simple solution processing. X-ray diffractions, scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis are used to study the structure and properties of these nanocomposites. The results indicate that graphene is dispersed on a molecular scale and aligned in the poly(vinyl alcohol) (PVA) matrix and there exists strong interfacial interactions between both components mainly by hydrogen bonding, which are responsible for the change of the structures and properties of the PVA/graphene nanocomposites such as the increase in T_g and the decrease in the level of crystallization.     

The influence of dehydration on the interfacial bonding,microstructure and mechanical properties of poly(vinyl alcohol)/graphene oxide nanocomposites

The relationship between the interfacial bonding, microstructure and mechanical properties of the poly(vinyl alcohol)/graphene oxide nanocomposites (PVA/GO) has been investigated by controlling the water content through a dehydration process. The interfacial bonding in PVA/GO was predominantly by hydrogen bonds which were strongly affected by the dehydration process. Micro-voids in the microstructure formed after dehydration due to the shrinkage of the fibrils. A variety of hydrogen bonds including water–water, water–GO and water–PVA can be replaced with the strong PVA–GO interfacial bond resulting in a transition from ductile to brittle fracture. The tensile modulus and strength properties of the PVA and PVA/GO increased as the amount of residual water reduced, while the fracture strain was decreased. The surface mechanical properties of PVA/GO measured by nanoindentation showed broadly similar trends with water content as the bulk mechanical properties. However, there was a threshold value of approximately 3 wt.% water below which the surface mechanical properties decrease slightly. The indentation modulus was higher than the tensile modulus by a factor of at least three. The combined influence of the microstructure and the distribution of water in the nanocomposite is considered to be responsible for this.