Anita Ptiček Siročić

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.

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.

Effect of modified nanofillers on fire retarded high-density polyethylene/wood composites

In this study fire retarded HDPE/WF composites based on high density polyethylene (HDPE) and wood flour (WF) were investigated. Polymer and WF ratio was kept at 70/30 while concentration of fire retardant was 20 mass %. Ammonium polyphosphate and aluminum hydroxide were used as fire retardants. To diminish the influence of high loadings of fire retardants on mechanical properties two different types of organically modified nanofillers (CaCO3 and SiO2) were used. Surface modification of HDPE polymer and nanofiller was done to enhance the compatibility in composite and improve the mechanical properties and fire performance. Mechanical properties were characterized by dynamic mechanical analysis while compatibility of components in composites was followed through morphology by scanning electron microscopy. Thermal and fire properties were characterized by thermogravimetric analysis, pyrolysis combustion flow calorimetry, and limiting oxygen index. The obtained results show that addition of surface modified nanofiller considerably affects the morphology resulting in the enhancement of mechanical and fire properties. Ammonium polyphosphate fire retardant in combination with SiO2 nanofiller showed the highest limiting oxygen index value, the lowest heat release rate, and total heat released in pyrolysis-combustion flow calorimetry test indicating best overall fire performance.

The surface energy as an indicator of miscibility of SAN/EDPM polymer blends

Surface properties of blends prepared of styrene-acrylonitrile and ethylene-propylene-diene changing the homopolymer proportions and compatibilized by high impact polystyrene have been studied by contact angle measurement. The surface free energy of interphase of homopolymers pairs, work of adhesion, and wetting coefficient were calculated using Wu’s geometric mean method and the total surface free energy and acid–base components of the blends by using van Oss, Good and Chaudhury method. Blends were also characterized by dynamic mechanical analysis and by scanning electron microscopy. The miscibility of studied blends was estimated through changes of surface free energy, energy of interface and through the shifts of glass transition temperature and changes in morphology. From the results, it can be seen that added compatibilizer reduces the interface energy and provides more homogenous system by interfacial segregation and rearrangements of molecules at the blend surface. The results of morphological observations reveal that the addition of a small percentage of compatibilizer decreases the domain size of the dispersed phase and enhances the compatibility of the blends.

Effect of preparation on morphology-properties relationships in SAN/EPDM/PCC composites

Mechanical and morphological properties of composites containing styrene—acrylonitrile (SAN) copolymer, ethylene— propylene—diene (EPDM) polymer, and different types of precipitated calcium carbonate (PCC) were investigated and their properties were analyzed in regard to PCC surface properties and the way of sample preparation (with or without use of a masterbatch (MB)). Contact angles of test liquids on PCC samples were measured in order to determine surface free energies of filler and to predict strength of filler—polymer interactions. Filler—polymer interactions play a significant role in determining preferential localization of the filler in the composite. The tensile and impact strength results of the composites without the MB show much higher values than composites prepared with the MB. Significant decrease of tensile strength is observed for the samples prepared with the MB due to change in morphology, which is elongated dispersed EPDM particles in SAN matrix, compared to the samples prepared without the MB that have droplet morphology.

Effect of the Filler and the Compatibilizer on the Properties of Filled Blends

In this work, the mutual effect of the filler aluminum hydroxide Al(OH)3 and the compatibilizers ethylene–propylene copolymer (EPR) and ethylene–vinyl acetate copolymer (EVA) on the properties of blends based on polyethylene (PE) and polypropylene (PP) was studied. The microstructural and morphological changes as well as mechanical features of samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and by tensile tests. Morphology of the samples prepared with the compatibilizers and filler is much finer in comparison to virgin blend. Due to established interaction between components that enhance the intimate adhesion among the components finer droplets dispersion within the blends matrix is observed. The addition of the filler and compatibilizers produced an increase in the elasticity particularly for the samples prepared in two-stage extrusion process where filler is first extruded with PE matrix and then extruded with other polymers of the blends.

Kinetic analysis of thermal and thermo-oxidative degradation of polyethylene (nano)composites

Thermal properties and degradation of polyethylene LDPE (nano)composites were investigated by isoconversional thermogravimetric analysis in air and nitrogen atmosphere by applying the Kissinger–Akahira–Sunose method. Low-density polyethylene (LDPE) composites containing 3 wt.% nanofiller Cloisite 20A and 4, 6, and 8 wt.% of natural zeolite were prepared using extrusion/injection moulding. The parameters of thermal stability of the samples were determined i.e. onset temperature of the degradation (T90), which exhibit initial mass loss (10 mass %) and maximum loss rate temperature (Tmax). Also, activation energy (Ea) of samples was calculated and interpreted in terms of thermal degradation mechanisms. Under nitrogen, the thermal degradation of LDPE (nano)composites follows a random scission pathway but it was retarded and slowed by the presence of the fillers. The results show that thermo-oxidative degradation of studied (nano)composites is induced at lower temperatures and appears as much more complex and multi-stage process.

Cleaning efficiency of poly(ethylene terephthalate) washing procedure in recycling process

This work demonstrates the poly(ethylene terephthalate) (PET) washing process, which is the very important step in the overall PET recycling procedure. The samples of waste PET bottles were washed in sodium hydroxide at two different temperatures, that is, at 70 and 75°C, at a time intervals of 15 and 30 min. The cleaning efficiency of the washing processes was determined through the identification of the residual impurities and products of PET degradation. The samples before and after the washing procedure were characterized by gas chromatography/mass spectrometry (GC/MS), gel permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. Due to low obtained oligomer molecular masses, it can be concluded that the degradation during all washing processes is not strong. Results show good purity of washed PET, especially at 75°C, due to very low content of adhesives, toxic compounds and formed monomers. The washing process carried out at 75°C for 15 min can be considered as the most successful. It results with low polymer degradation and the removal of the high quantity of contaminants in short time interval.

Assessment of Groundwater Vulnerability in Croatian Karstic Aquifer in Jadro and Žrnovnica Springs Catchment Area

The groundwater vulnerability assessment is based on the evaluation of physical, chemical, and biological properties of the environment which can provide a certain degree of protection to the groundwater from contamination. In this paper are presented results of application four different methods (SINTACS, EPIK, PI, and COP) for groundwater vulnerability assessment in karstic aquifer in Croatia. The main objectives of the study were to apply the methods on test site where, so far, groundwater vulnerability was never assessed, then to modify the methods in order to improve adaptation to the research field and available data. After comparing vulnerability maps obtained by all four presented methods, it was determined that the most appropriate method is COP + K, which was additionally modified. Although presented methodology is not new, it can be used as a background for land-use planning, because it identifies parts of the catchment area that are, due to its natural features, more vulnerable to human impact. It can be also applied as an additional tool in groundwater protection for delineation of protection zones, and provides very useful data in various fields of water management, especially for karst area in Croatia.