Ljerka Kratofil Krehula

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.

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.

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.

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.

Study of masterbatch effect on miscibility and morphology in PET/HDPE blends

The present work studies the morphology in poly(ethylene-terephthalate)/polyethylene (PET/HDPE) polymer blends and its impact on blend properties. Mixing process in blend preparation is the important parameter for the type of obtained blend morphology and final blend properties, so two different mixing processes were used. In the first one, all components are mixed together while another one includes two step mixing procedure using two different types of masterbatch as compatibilizers for PET/HDPE system. Such blends can be considered in terms of PET polymer recycling in the presence of HDPE impurities in order to find suitable compatibilizers, which will enhance the interactions between these two polymers and represents the possible solution in recycling of heterogeneous polymer waste. The morphology of the studied PET/HDPE blends was inspected by scanning electron microscopy to examine the influence of the mixing process and various compositions on blends morphology, and interactions between PET and HDPE. The surface properties were characterized by contact angle measurements. The effect of the extrusion on the samples thermal behaviour was followed by DSC measurements. FTIR spectroscopy was used for the determination of interactions between blend constituents. It can be concluded that the type of mixing process and the carefully chosen compatibilizer are the important factors for obtaining the improved compatibility in PET/HDPE 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.

Surface characteristics and enhancement of water vapour properties of paperboard coated with polycaprolactone nanocomposites

Abstract Offset printed paperboard coated with polycaprolactone (PCL) polymer and nanoparticles was studied to elucidate the interactions and adhesion in two-layered packaging material. SiO2, Al2O3 and ZnO nanoparticles were used due to their specific interactions with water vapour that results in inhibition of water permeability. The good dispersion of nanoparticles in PCL matrix is crucial for enhancement of the barrier properties of coated paperboard. To gain an insight into the interactions between the nanoparticles, paperboard and PCL matrix determination of surface parameters was performed. The samples were characterized for water vapour permeability, mechanical and thermal properties. Their morphology was analysed by SEM microscopy, FTIR and UV/Vis spectroscopy. UV stability of the PCL nanocomposites coatings was also studied. It can be concluded that the nanoparticles have a significant effect on the surface properties and they influenced adhesion between paperboard and PCL coating.

Study of PET depolymerization during recycling

Abstract Depolymerization of poly(ethylene-terephthalate) (PET) in PET/HDPE blends, obtained from virgin polymers during mechanical recycling was studied. Extrusion of PET/HDPE blends was simulation of the first cycle of recycling and extrusion of the blends with EPDM/HDPE (E-M) masterbatch and HDPE/EPDM (PEM) masterbatch the second cycle. After that the samples were additionally treated to examine their thermooxidative stability. Blends were characterized by determination of the concentration of carboxyl groups by Pohl titration, by FTIR spectroscopy and differential scanning calorimetry (DSC) to determine crystallization (Tc) and melting (Tm) temperatures. The concentration of determinated carboxyl end groups in blends indicate presence of formed polymer radicals with hydroxyl-carboxyl end groups as the result of depolymerization of PET. Presence of characteristic groups was also confirmed by FTIR. DSC results indicate the influence of HDPE on crystallization temperature of PET and points to the fact that even degraded samples maintain the chemical structure of PET. From the results it can be seen that addition of the particular modifier can reduce and even prevent the depolymerization during the recycling process.