Zlata Hrnjak-Murgić

Molecular and Morphological Characterization of Immiscible SAN/EPDM Blends Filled by Nano Filler

The compatibilizing effect of nano sized calcium carbonate filler on immiscible blends of styrene-co-acrylonitrile/ethylene propylene diene (SAN/EPDM) was examined. The surface energy of the calcium carbonate was modified by stearic acid. The compatibility of SAN/EPDM blends was studied by following the glass transition temperature T g by DSC. SEM was used to observe the blend morphology and the X-ray analyzer was used to detect the calcium from filler in samples. Mechanical properties of the blends were determined, and related to changes of polymer-filler interactions and morphology. The results suggest that the morphology of the SAN/EPDM blends studied was affected by the reduction of surface energy of the filler.

Development of low density polyethylene nanocomposites films for packaging

Requirements for adequate permeability of polymeric materials to gases and vapors, good barrier and mechanical properties of polymers have boosted interest in developing new strategies to improve these properties. Research and development in polymeric materials coupled with appropriate filler, matrix-filler interaction and new formulation strategies to develop composites have potential applications in various types of packaging (agricultural produce, dried food, frozen food etc.). In this study, LDPE composites containing various types of fillers (zeolite TMAZ 7, nanoclay Cloisite 20A and precipitated calcium carbonate, CaCO3) were prepared using extrusion/injection molding. The microstructural and morphological changes as well as mechanical features of samples were characterized by scanning electronic microscopy and by tensile tests. The thermal degradation of LDPE composites was studied using thermogravimetric analysis. Barrier properties (permeability, the diffusion and the solubility constant) in modified LDPE samples were determined. It is found that used minor clay concentration is already very effective for achievement of good morphology. In the presence of nanoparticles, at lower content, the value of oxygen permeability of LDPE decreases. Also, the results have revealed that the samples containing fillers have increased thermal stability in comparison to pure LDPE.

Weathering of High-Density Polyethylene-Wood Plastic Composites

Abstract Due to the widespread use of wood-plastic composites (WPCs), high-density polyethylene-wood flour composites (HDPE/WF) were studied in order to determine their stability in different application conditions. UV degradation and periodic absorption/desorption of moisture cause damaging changes to material during WPCs’ exterior application, so it is necessary to ensure WPCs’ durability against atmospheric influences. Samples were characterized by FTIR spectroscopy and scanning electron microscopy (SEM) in order to study the degradation after simulated weathering. The degree of water absorption was also determined. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used for the determination of composites’ thermal properties. Results show that the stability of the HDPE/WF composites to UV treatment highly depends on stabilizer content and its dispersion in the polymer matrix. Incompatibility of HDPE and wood particles is a major problem that should be solved to achieve good durability and satisfying properties in use.

Influence of the network on the interaction parameter in system EPDM vulcanizate-solvent

Swelling measurements in six organic solvents were carried out on samples of dicumyl peroxide crosslinked ethylene–propylene–diene (EPDM) having various crosslink densities. The Flory–Huggins interaction parameter χ was determined for EPDM vulcanizates 312 and 812 as well as their mixture 312/812 using the Flory–Rehner equation. The results show that the χ parameter for the crosslinked polymer is greater than for the uncrosslinked one and is a linear function of the crosslink density. The swelling behavior of the networks were also interpreted by the Flory–Erman theory using the structural factor F4′ to characterize the network and its behavior during the swelling. The obtained χ values indicate that broadening of the molecular mass distribution, in the Gaussian region of distribution, mixture 312/812, increases interactions with solvents.

Properties of UV protective films of poly(vinyl-chloride)/TiO2 nanocomposites for food packaging

This work studies the UV protection properties of poly(vinyl-chloride) (PVC) nanocomposites. A functional property of UV protection is achieved by adding the active component (titanium dioxide (TiO2) or titanium dioxide modified with silver nitrate and copper nitrate) to the PVC matrix. PVC nanocomposites were prepared by extrusion and then pressed into films. Prepared PVC nanocomposites were characterized by thermogravimetric analysis, UV–Vis spectroscopy, X-ray diffraction and scanning electron microscopy. The mechanical properties and antimicrobial activity were also studied. The results show that PVC nanocomposites’ thermal stability is improved in relation to a pure PVC polymer. The thermal stability and antimicrobial efficiency increase when higher silver nitrate content is used. The sample prepared with silver and copper nitrate shows the best thermal stability due to a modified mechanism of thermal degradation. Samples where nanoparticles are homogeneously dispersed in the polymer matrix show good mechanical properties. The results also show that adding the active component TiO2 modified with silver ions contributes to the improved UV protection property of nanocomposite materials.

Stability and Synergistic Effect of Polyaniline/TiO2 Photocatalysts in Degradation of Azo Dye in Wastewater

The polyaniline/TiO2 (PANI/TiO2) composite photocatalysts were prepared by the in situ chemical oxidation of aniline (An) in the presence of TiO2 particles. For this purpose, photocatalysts with different amounts of PANI polymer were prepared and analysed. Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis indicated successful synthesis of the PANI polymer and its conductivity was also determined. The micrographs of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to explain the impact of the aniline amount on the aggregation process during the synthesis of the composites. The smallest size of aggregates was obtained for the photocatalysts with 15% of PANI (15PANI/TiO2) due to the formation of homogenous PANI. The photocatalytic activity of studied PANI/TiO2 photocatalysts was validated by monitoring the discoloration and mineralization of Reactive Red azo dye (RR45) in wastewater. The 15PANI/TiO2 sample presented the highest photocatalytic efficiency under ultraviolet A (UVA) irradiation, in comparison to pure TiO2. This was explained by the formation of uniformly dispersed PANI on the TiO2 particles, which was responsible for the synergistic PANI-TiO2 effect.

Polyethylene/Polycaprolactone Nanocomposite Films for Food Packaging Modified with Magnetite and Casein: Oxygen Barrier, Mechanical, and Thermal Properties

ABSTRACT Polyethylene (PE) was modified and prepared as double-layer polyethylene/polycaprolactone (PE/PCL) film. Magnetite and casein were added to the PCL-coating film to improve barrier properties and prevent destruction of basic structure of primary polymer PE. Significant improvements were observed with regards to mechanical (tensile strength, elongation at break) and thermal properties, while barrier (O2 permeability) properties were slightly improved. Overall migration values into acetic acid were lower (from 1 to 4.6 mg/dm2) than the upper limit set by the legislation. Specific migration of iron in PE/PCL-Fe samples is also below (µg/L) specific migration limit value set by the legislation (mg/kg). GRAPHICAL ABSTRACT

Change of network structure of natural rubber vulcanizate with thermal aging

The effect of sulfur accelerators during the curing process in natural rubber (NR) was investigated. The samples were prepared by adding the same fraction of various types of accelerators in the compound and all samples were cured at the same temperature but for two different times. Determination of the molecular massbeween crosslinks immediately after vulcanization shows the crosslink density in the samples, which differs for different accelerators. After that, the same samples undergo thermal aging and the changes of the crosslink dinsity were studied. During the first period of thermal aging, additional crosslink were observed and then a period of deterioration of the network structure is following. From the obtained relults of the molecular mass between crosscan be drawn about the most suitable accelerator for use in certain conditions and applications. To predict the behavior of vulcanizates under various effects as heat and radiation, it is important to know more about the chemical structure of the network. The changes of crosslink density in the investigated samples were followed by eqiomobrium swelling and by mechanical measurements. IR spectroscopy was used to study the changes of the crosslink bridges. The influence of aging time on the maximum tensile strength, for NR vulcanizates cured 5 min.

Preparation and Properties of Low Density Polyethylene Film Modified by Zeolite and Nanoclay

PE-LD samples containing two types of filler in concentrations of 2–10 wt.% (zeolite TMAZ 7 and nanoclay Cloisite 20A). The microstructural and morphological changes as well as mechanical features of samples were characterized by scanning electronic microscopy (SEM) and by tensile tests. The thermal degradation of PE-LD composites were achieved using thermogravimetric analysis (TGA). The permeability, the diffusion and the solubility constants of the gases in modified PE-LD films were calculated and the gas separation (N2/O2; O2/CO2) ability was determined. In the presence of nanoparticles, at lower content, the value of oxygen permeability of PE-LD decreases.

Study of the Compatibilizer Effect on Blends Prepared from Waste Poly(ethylene-terephthalate) and High Density Polyethylene

Abstract In this work mechanical recycling of waste poly(ethylene-terephthalate) (PET) in the presence of high density polyethylene (HDPE) was studied. The fraction of HDPE in PET/HDPE blends was 3, 5, 6 and 10 wt.%. Isocyanate HI compatibilizer was first synthesized and then added to the blends at a fraction of 5 wt.%. Ethylene-propylene-diene masterbatch (EPDM-M) was prepared by mixing and added in fraction of 15, 30 and 50 wt.%. All PET/HDPE blends studied were characterized by scanning electron microscopy SEM, differential scanning calorimetry DSC and melt flow rate (MFR). Blends prepared with isocyanate HI compatibilizer were also studied by FTIR spectroscopy. Appearance of new vibrations in the FTIR spectra confirms that during the blending reactions between isocyanate HI compatibilizer and blend components appear. Results show that used compatibilizers significantly improved compatibility of polymers in studied blends. From the results it is obvious that immiscibility of PET and HDPE can be overcome.