Ali Durmus

Mechanical Properties of Linear Low‐density Polyethylene (LLDPE)/clay Nanocomposites: Estimation of Aspect Ratio and İnterfacial Strength by Composite Models

In this study, mechanical properties of the linear low‐density polyethylene (LLDPE)/org‐clay nanocomposites prepared by melt processing were investigated. Aspect ratio (A f ) of the clay layers were estimated by using the Halpin‐Tsai (H‐T) micromechanical model based on the enhancement of the Youngs modulus (E) with the clay loading (φ). Strength of interfacial interactions (τ and B parameters) between the clay layers and polymer chains were also quantified by two indirect modeling approaches based on the improvement in tensile strength (or yield stress) of the nanocomposite samples. Interfacial strength parameters, τ and B, were found as about 5 MPa and 17.3, respectively. The average value of A f was calculated as ∼35 by the H‐T model. In the TEM study, it was observed that the nanocomposite samples showed mixed morphology that could be defined as some exfoliated layers, intercalated clay stacks, and two to three layered tactoids present together within the samples. An estimated A f value was also confirmed by the TEM study. On the other hand, it was also shown that the A f value is consistent with previously reported values calculated by the modeling of melt rheological data of samples obtained from dynamic oscillatory shear measurements.

Isothermal crystallization kinetics of glass fiber and mineral-filled polyamide 6 composites

In this study, isothermal crystallization kinetics of polyamide 6 (PA6) composites reinforced with surface-treated glass fiber (GF) and natural, clay-type mineral (MN) were investigated by differential scanning calorimetry method in the presence and absence of a nucleating agent (NA). Microstructural features of the composites and interfacial interactions between filler and polyamide phases were also quantified by rheological measurements. The kinetic parameters for the isothermal melt-crystallization process of the samples were determined with the Avrami and Lauritzen–Hoffman models. The crystallization activation energies were determined by the Arrhenius method. It was found that the both fillers yielded a significant increase in the storage modulus of PA6. Kinetic calculations showed that the MN has a more pronounced acceleration effect on the crystallization rate of PA6 than the GF. Introduction of a small amount of NA significantly favored the isothermal crystallization rate of GF-reinforced PA6 but did not accelerate that of MN-reinforced one. Based on the results, it has been highlighted that PA6 composites reinforced with surface-treated GFs and including a small amount of clay-like mineral as a cheap and easy-accessible minor filler could yield the best performance for the injection-molded PA6 parts because the GF enhances the mechanical properties and the clay-like mineral accelerates the crystallization rate.

Effects of Halloysite Nanotube on the Mechanical Properties and Nonisothermal Crystallization Kinetics of Poly(Butylene Terephthalate) (PBT)

In this study, poly(butylene terephthalate) (PBT)/halloysite composites having various amounts of halloysite, as a one-dimensional (1D) nanotubular alumina-silicate filler, were prepared by melt processing in a twin screw extruder. Nonisothermal crystallization behaviors of the samples were studied by DSC and XRD methods. The effect of halloysite amount on the nonisothermal melt crystallization kinetics of the PBT was analyzed with various kinetic models, namely the Ozawa, Avrami modified by Jeziorny, and Liu–Mo. Crystallization activation energies of the samples were determined by the Kissinger model. Viscoelastic properties of the samples were studied by DMA tests. By comparing the effect of halloysite amount on the melt crystallization kinetics of PBT, it was found that halloysite increased the crystallization rate of PBT. Crystallization activation energy values of the PBT and composite samples including 2%, 5%, and 10% of halloysite were found to be −341.8, −353.3, −373.6, and −419.6 kJ/mol, respectively. Based on the DMA tests, it was found that halloysite increased the elastic feature of the sample due to polymer-filler interactions.

Comparing of melt blending and solution mixing methods on the physical properties of thermoplastic polyurethane/organoclay nanocomposite films

In this study, microstructural features and physical properties of thermoplastic polyurethane (TPU)/organoclay nanocomposites films prepared via melt blending (MB) and solution mixing (SM) methods were investigated in detail. Amount of organoclay into the composition varied in the range of 2 and 8 wt%. Microstructural properties of samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) methods. It was found that the organoclay layers exhibited better dispersion, exfoliated, and semi-exfoliated structure in the MB samples than the SM counterparts. Viscoelastic properties of samples were also studied by measuring the rheological behaviors of bulk samples in an oscillatory rheometer in the melt state and measuring of the time-dependent nonlinear creep behaviors of film samples in a dynamic mechanical analyzer in the solid state. Gas and water vapor permeability (WVP) values of nanocomposite films were measured. Based on the melt rheology measurements, it was found that the MB samples showed characteristic solid-like behavior and higher improvement in storage modulus at low-frequency region. Creep behaviors of samples were also quantified with the four-element Burger model. It was found that the introducing of organoclay into the composition via MB method yielded more improvement in the creep resistance, gas, and WVP values of films than the SM counterparts, possibly due to the better dispersion of organoclay layers into the TPU structure. Based on the improvement in permeability and mechanical properties of the samples and also SEM and TEM observations, the average aspect ratio value (A f) of organoclay stacks was estimated in the range of 15–20 for the MB samples.

Effect of Wood-derived Charcoal Content on Properties of Wood Plastic Composites

The effect of wood‑derived charcoal flour on the water resistance and mechanical properties of wood plastic composite (WPC) panels was investigated. The hot press molded WPC panels were produced from polypropylene (37 wt%) with maleic anhydride-grafted polypropylene (MAPP, 3 wt%) and different mixtures of wood flour and charcoal flour. The amount of charcoal flour was gradually increased up to 60 wt%. The thickness swelling and water absorption of WPC panels considerably decreased with increasing charcoal flour content. The internal bond strength and bending properties of the WPC panels significantly improved with increasing charcoal flour content. This was mainly attributed to the high amount of pores and gaps in the charcoal flour. Melted polypropylene could get into the pores and gaps during the hot press molding, which lead to a better interfacial adhesion between polymer matrix and wood filler. The results showed that the charcoal flour could be partially substituted for the wood flour in the production of WPC panels having higher dimensional stability and internal bond strength.

Effects of various polyolefin copolymers on the interfacial interaction, microstructure and physical properties of cyclic olefin copolymer(COC)/graphite composites

In this study, effects of various types of functional polyolefin copolymers (FPOCs), poly(isobutylene-alt-maleic anhydride), poly(maleic anhydride-alt-1-octadecene) and poly(ethylene-graft-maleic anhydride), on the microstructure formation, interfacial interaction and physical properties of cyclic olefin copolymer (COC)/graphite composites were investigated. The COC/graphite composites were prepared in a lab. scale twin screw extruder. Microstructural features of samples were studied in a field emission scanning electron microscopy (FESEM). Viscoelastic properties of samples, obtained from the rheology tests in melt state and the dynamic mechanical analysis in solid state were used to quantify interfacial interactions between the COC and graphite depending on the types of FPOC. The average aspect ratio (Af) values of graphite flakes in the COC phase were determined about 40–65 by SEM observation and image analysis study on the samples prepared with different types of FPOC. Based on the gas permeability measurements, tortuous diffusion model suggested that the Af values of graphite flakes varied between 40 and 80 depending on the amount of graphite. It was shown that the poly(isobutylene-alt-maleic anhydride) copolymer provided relatively higher interfacial interaction between the COC and graphite flakes than the other FPOCs.

Rheological and mechanical properties of cycloolefin copolymer/organoclay nanocomposites

In this study, structural, rheological and mechanical properties of cycloolefin copolymer/organoclay nanocomposite films were investigated in detail. A maleic anhydride grafted polyethylene was used as conventional compatibilizer. In a series of samples, poly(ethylene-co-1-octene) copolymer was also used as a secondary component in the sample formulations. Microstructural features of the samples and clay dispersion into the polymer phase were characterized by X-ray diffraction and scanning electron microscopy studies. Physical properties of the samples were examined with the melt rheology and dynamic mechanical analysis tests. Highly transparent films with the intercalated nanocomposite structure were successfully obtained. It was found that the poly(ethylene-co-1-octene) enhances the organoclay dispersion into polymer phase and the related physical properties of the samples. Some structural properties of the samples such as the critical volume fraction of organoclay (ϕp) and aspect ratio (Af) were quantified with the experimental data obtained from the rheological and mechanical measurements. Critical volume fraction of organoclay at the percolation threshold was determined as 0.018 based on the rheological measurements. The Halpin–Tsai micro-mechanical model for composite materials was employed to determine dispersion of organoclay layers. The aspect ratio of organoclay tactoids was found to be about 12–15 based on the both rheological and micro-mechanical modeling.

Structurally Enhanced Hydrogel Nanocomposites with Improved Swelling and Mechanical Properties

In this work, structurally enhanced hydrogel nanocomposites based on 2-acrylamido-2 methyl propane sulfonic acid (AMPS)-acrylamide (AAM) copolymer with high hydrophilic group content were prepared by in-situ copolymerization by using different types of clay (montmorillonite, mica and halloysite). Nanocomposite hydrogels were characterized by Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray diffraction (XRD) analyses and determination of swelling degrees of the samples. Mechanical properties of the samples were also investigated by determination of the compressive elastic modulus. It was also found that exfoliated or highly expanded intercalated nanocomposite structure was obtained and clay incorporation into the AMPS-AAM hydrogel structure improved its swelling capacity. The highest swelling capacity (1030 g H2O/g) was observed for the nanocomposite sample prepared with the montmorillonite amount of 5% (w). Furthermore, mechanical strength of the hydrogels against compression forces was significantly improved by the clay addition. It was found that the type of clay, in other word filler geometry, affected the compressive elastic modulus (E) of the samples. It was concluded that halloysite, which is considered to be a one dimensional (1D) nanotubular filler was less effective to enhance the compressive elastic modulus (E) of such materials compared with the montmorillonite and mica having two dimensional (2D) platelet or disk-like shapes at a particular amount of clay.

Investigation of morphological, rheological, and mechanical properties of cyclic olefin copolymer/poly(ethylene-co-vinyl acetate) blend films:

In this study, cyclic olefin copolymer/poly(ethylene-co-vinyl acetate) 90/10, 80/20, and 70/30 blends were prepared by melt processing in a twin screw extruder equipped with a cast film haul-off unit to make films. Microstructural, rheological, mechanical, and viscoelastic properties of film samples were investigated by various tests performed in scanning electron microscope, rotational rheometer, dynamic mechanical analyzer, and tensile test machine. We observed that the films exhibited characteristic immiscible “matrix–droplet” or “cocontinuous” blend morphology, depending on the sample composition. Based on the melt rheology and dynamic mechanical analyzer tests, we found that poly(ethylene-co-vinyl acetate) addition changed the viscoelastic properties of cyclic olefin copolymer such as increasing short-term creep strain and relaxation time but reducing relaxation rate in solid state. One can conclude that such effects became more pronounced by adding a compatibilizer (PE-g-MA) at 50% of poly(ethylene-co-vinyl acetate) present in the composition. We also found that poly(ethylene-co-vinyl acetate) addition into cyclic olefin copolymer reduced the Young’s modulus and yield stress and increased the strain at break for the blends.

Quantifying effects of compositional variations on microstructural properties of polypropylene-wood fiber composites by melt rheology and tensile test data:

In this study, melt-state rheological behavior and solid-state mechanical properties of polypropylene-wood fiber composites were investigated in detail depending on compositional variations such as (i) alkaline treatment on wood fibers, (ii) fiber size, (iii) wood fiber content, and (iv) compatibilizer/wood fiber ratio. Composite samples were prepared in a lab-scale co-rotating twin screw extruder by using a maleic anhydride grafted polypropylene as compatibilizer. Morphological features of composites were examined in a scanning electron microscopy. Viscoelastic behavior and mechanical properties of samples were analyzed by performing oscillatory tests in a rotational rheometer and a universal tensile test machine. It was found that the increasing amounts of wood fiber and compatibilizer/wood fiber ratio led to improve melt elasticity and tensile strength. It was concluded that the amount of compatibilizer into composite formulation was the most important compositional parameter compared to size and chemical treatment of wood fibers for improving the physical properties of composites. The Nicolais-Nicodemo micromechanical model showed that the increasing amount of compatibilizer yielded lower parameters which implied better interfacial adhesion between polypropylene and wood fibers.