Hossein Ali Khonakdar

An investigation of chemical crosslinking effect on properties of high-density polyethylene

High-density polyethylene (HDPE) was chemically crosslinked with various amounts of di-tert butyl cumyl peroxide (BCUP). Crosslink density determined by rubber elasticity theory using hot set test showed an increase with increasing BCUP. Glass transition temperature (Tg), thermal stability, crystallization, melting behavior and tensile properties were studied. The results showed a new finding about decrease in Tg as a consequence of the ‘chemical crosslinking’ of HDPE. This was explained by observed reduction in crystallinity and expected increase in free volume as a result of restriction in chain packing. However, chemical crosslinking had no significant effect on the thermal stability. The stress at break, Youngs modulus yield strength and elongation at break generally decreased with increase in BCUP. By increasing the temperature for slightly crosslinked HDPE, the elongation at break was increased but by increasing the crosslinking level an opposite effect was observed. Crosslinked HDPE showed an decrease in creep strain and an increase in creep modulus with increasing BCUP.

Thermal and shrinkage behaviour of stretched peroxide-crosslinked high-density polyethylene

Abstract The thermal shrinkage of stretched crosslinked high-density polyethylene (HDPE) was investigated with the aim to produce heat shrinkable materials. The heat shrinkable property was achieved by a process of heating–stretching–cooling by aid of tensile machine on crosslinked HDPE obtained by compounding with various amount of peroxide. Effect of stretching ratio and stretching temperature on thermal and shrinkage behaviour at varying peroxide contents was investigated. The results showed that crosslinking hindered the crystallization process by decreasing the melting and crystallization temperatures as well as the total degree of crystallinity. The stretching ratio had no significant effect on shrink temperature but rather on ultimate shrinkage. The stretching temperature had relatively significant influence on the shrink temperature. Crosslinked HDPE stretched at above melting point (140 °C) had higher shrink temperature as compared to those stretched at lower temperature (90 °C). These effects could be reasonably explained by Hoffman theory and changes in crystallites size and total amount of crystallinity.

Cure Kinetics of Epoxy Nanocomposites Affected by MWCNTs Functionalization: A Review

The current paper provides an overview to emphasize the role of functionalization of multiwalled carbon nanotubes (MWCNTs) in manipulating cure kinetics of epoxy nanocomposites, which itself determines ultimate properties of the resulting compound. In this regard, the most commonly used functionalization schemes, that is, carboxylation and amidation, are thoroughly surveyed to highlight the role of functionalized nanotubes in controlling the rate of autocatalytic and vitrification kinetics. The current literature elucidates that the mechanism of curing in epoxy/MWCNTs nanocomposites remains almost unaffected by the functionalization of carbon nanotubes. On the other hand, early stage facilitation of autocatalytic reactions in the presence of MWCNTs bearing amine groups has been addressed by several researchers. When carboxylated nanotubes were used to modify MWCNTs, the rate of such reactions diminished as a consequence of heterogeneous dispersion within the epoxy matrix. At later stages of curing, however, the prolonged vitrification was seen to be dominant. Thus, the type of functional groups covalently located on the surface of MWCNTs directly affects the degree of polymer-nanotube interaction followed by enhancement of curing reaction. Our survey demonstrated that most widespread efforts ever made to represent multifarious surface-treated MWCNTs have not been directed towards preparation of epoxy nanocomposites, but they could result in property synergism.

Development of one-step synthesized LDH reinforced multifunctional poly(amide–imide) matrix containing xanthene rings: study on thermal stability and flame retardancy

New exfoliated poly(amide–imide)/Zn–Al layered double hydroxide (LDH) nanocomposites were synthesized by solution intercalation using synthesized organo-modified LDH (OLDH) as nanofiller obtained by one-step method. The designed poly(amide–imide) (PAI) containing bulky xanthene rings in the side chains, aliphatic chains in the main chains and amide groups in the side and main chains was synthesized via direct polycondensation reaction with desired molecular weight. Poly(amide–imide)/LDH nanocomposites (PAINs) were prepared by different contents of OLDH and morphology, mechanical, thermal and flame retardancy of PAINs were studied. The dispersion of OLDH was quantified by X-ray diffraction (XRD) and transmission electron microscopy (TEM) and the results showed a good dispersion for OLDH in the PAI matrix. According to the results of mechanical tests, the tensile strength of PAIN containing 5 mass% of OLDH increased to 70.1 MPa from 57.3 MPa of neat PAI without OLDH addition. The thermogravimetric analysis (TGA) results showed that the addition of OLDH resulted in a substantial increase in the thermal stability of the PAINs. The temperature at 5% weight loss (T5) was increased from 281 °C to 323 °C for PAIN containing 5 mass% of OLDH as compared to neat PAI, as well the char yield enhanced greatly. Significant improvements in flame retardancy performance were observed for the nanocomposites from microscale combustion calorimeter (MCC) (reducing both the heat release rate and the total heat released).

Biowaste chicken eggshell powder as a potential cure modifier for epoxy/anhydride systems: competitiveness with terpolymer-modified calcium carbonate at low loading levels

Biowaste chicken eggshell (ES) powder was applied as a potential cure modifier in epoxy/anhydride systems. Cure behaviour and kinetics of composites filled with very low content (0.1 wt% based on epoxy resin) of ES, calcium carbonate (CaCO3), and terpolymer-modified fillers, mES and mCaCO3, were discussed comparatively. Surface analysis was performed by X-ray photoelectron spectroscopy. Cure kinetics was investigated by differential (Friedman) and integral (Ozawa and Kissinger–Akahira–Sunose) isoconversional methods using dynamic differential scanning calorimetry (DSC) data. Overall, protein precursors naturally existing in the structure of pristine ES facilitated crosslinking of epoxy and hardener of anhydride with functional groups resulting from terpolymer attachment to CaCO3 particles. Accelerated/hindered cure was observed depending on the filler type and surface characteristics, as investigated via the autocatalytic/non-catalytic nature of reactions and comparison of activation energy values of four types of composites. An enhanced cure was identified for composites containing untreated ES, which could be inferred on account of the lower competitive cure of carboxyl groups in the terpolymer backbone with epoxy compared to peptide groups existing in microporous pristine ES. On the other hand, mCaCO3 revealed low values of activation energy compared to pristine CaCO3, but still of the same order as ground biowaste ES.

Investigating the role of surface micro/nano structure in cell adhesion behavior of superhydrophobic polypropylene/nanosilica surfaces

The main aim of the current study was to investigate the effects of different topographical features on the biological performance of polypropylene (PP)/silica coatings. To this end, a novel method including combined use of nanoparticles and non-solvent was used for preparation of superhydrophobic PP coatings. The proposed method led to a much more homogeneous appearance with a better adhesion to the glass substrate. Moreover, a notable reduction was observed in the required contents of nanoparticles (100-20 wt% with respect to the polymer) and non-solvent (35.5-9 vol%) for achieving superhydrophobicity. Surface composition and morphology of the coatings were also investigated via X-ray photoelectron spectroscopy and scanning electron microscopy. Based on both qualitative and quantitative evaluations, it was found that the superhydrophobic coatings with only nano-scale roughness strongly prevented adhesion and proliferation of 4T1 mouse mammary tumor cells as compared to the superhydrophobic surfaces with micro-scale structure. Such results demonstrate that the cell behavior could be controlled onto the polymer and nanocomposite-based surfaces via tuning the surface micro/nano structure.

Mechanical, rheological, and thermal behavior assessments in HDPE/PA-6/EVOH ternary blends with variable morphology

The mechanical, rheological, and thermal properties of various binary and ternary blends based on polyamide 6 (PA-6), high-density polyethylene (HDPE), and poly vinyl alcohol (EVOH) with variable morphology were comprehensively studied to give a perspective on interfacial adhesion situation. In this regard, transitions in the phase morphology of ternary systems were traced by means of scanning electron microscopic investigations, varying the type of matrix and composition in the minority phase. Theoretical and experimental analyses of impact and tensile properties provided support for the compatibilizing action of EVOH on HDPE/PA-6 immiscible blends. Rheological and thermal studies were also performed to make a broader image on the interphase region in ternary systems with core-shell and individually-dispersed minor domains. The most interesting finding was that there is a tendency for PA-6 to partially encapsulate HDPE domains within the EVOH continuous phase. This is roughly supported by SEM micrographs, but yield stress measurements placed too much emphasis on the morphological status.

Molecularly imprinted polymer nanoparticles for olanzapine recognition: application for solid phase extraction and sustained release

Recently, scientists have drawn more attention to polymeric nanoparticles as potential drug carriers. In this study, we synthesized high selective imprinted polymer nanoparticles using olanzapine as the template. The aim of this study was to prepare efficient imprinted polymer nanoparticles from an olanzapine template for the controlled release of olanzapine as a therapeutic drug for central nervous system (CNS) diseases at different pH values, and solid-phase extraction (SPE) as the sample clean-up technique combined with high-performance liquid chromatography (HPLC). The morphology of the nanoparticles was determined using scanning electron microscopy (SEM) images. Drug release, binding properties and dynamic light scattering (DLS) of the molecularly imprinted polymers (MIPs) were studied in this investigation. The adsorption isotherm was fitted with Langmuir and Freundlich models. The performance of the MIPs for the controlled release of olanzapine was assessed in two different media (SDS 1% and PBS). Results revealed that the MIPs have potential application in controlled drug release. Moreover, cytotoxicity of the MIP nanoparticles was measured on a NIH/3T3 cell line using a MTT method. Furthermore, the MIPs were applied to extract olanzapine from human blood plasma samples. The limit of detection (LOD) and limit of quantification (LOQ) were evaluated and were 0.18 μg L−1 and 0.39 μg L−1, respectively. These results collectively illustrate that MIP nanoparticles can be employed as an efficient technique for the extraction of the olanzapine from human plasma.

Superhydrophobic filter paper via an improved phase separation process for oil/water separation: study on surface morphology, composition and wettability

In this study, a novel method including the concurrent use of nanoparticles and non-solvent is proposed for surface modification of filter papers with the aim of achieving superhydrophobicity that can be used in oil/water separation applications. The effects of polymer, nanoparticle and non-solvent contents were investigated on the surface morphology, composition and wettability of the samples. A comparison was also made between the solution casting and dip-coating techniques. It was found that the dip-coating technique was not as efficient as solution casting because of the lower adsorption of polystyrene macromolecules onto the papers’ surfaces. Scanning electron microscopy results demonstrated the role of non-solvent in the surface morphology of the coatings. In fact, in the absence of non-solvent, superhydrophobicity was not achieved. X-ray photoelectron spectroscopy results confirmed that the presence of non-solvent also changed the surface composition of the coatings significantly. The optimum composition was found to have promising potentials in the separation of oil from water because of the induced superhydrophobic and superoleophilic properties. The findings of this fundamental research could be exploited in other systems for more efficient oil/water separating devices.

Tuning cell adhesion on polymeric and nanocomposite surfaces: Role of topography versus superhydrophobicity.

Development of surface modification procedures which allow tuning the cell adhesion on the surface of biomaterials and devices is of great importance. In this study, the effects of different topographies and wettabilities on cell adhesion behavior of polymeric surfaces are investigated. To this end, an improved phase separation method was proposed to impart various wettabilities (hydrophobic and superhydrophobic) on polypropylene surfaces. Surface morphologies and compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Cell culture was conducted to evaluate the adhesion of 4T1 mouse mammary tumor cells. It was found that processing conditions such as drying temperature is highly influential in cell adhesion behavior due to the formation of an utterly different surface topography. It was concluded that surface topography plays a more significant role in cell adhesion behavior rather than superhydrophobicity since the nano-scale topography highly inhibited the cell adhesion as compared to the micro-scale topography. Such cell repellent behavior could be very useful in many biomedical devices such as those in drug delivery and blood contacting applications as well as biosensors.