Polyolefins Journal
Volume:10 Issue: 3, Summer 2023

This work focuses on the damage of two thermoplastic materials; high density polyethylene "(HDPE)" and high impact polystyrene "(HIPS)". The contribution of this work is to determine the lifetime of these polymers by proposing a new static method, including different notches with different opening lengths instead of depth change, to predict the damage behavior of HDPE and HIPS. Three damage models were used to predict the lifetime of these polymers by a proposed simple method compared to the old complex methods. Chemical and microscopic analyses including Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) were performed. The results indicated that the shape of the notch and the morphological nature of the polymer influence the mechanical behavior of these polymers. The proposed experimental factors (life fraction as a function of notches) are in very good agreement with the experimental results.

In this study, reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize hydrophobic polystyrene (PS), poly(methyl acrylate) (PMA), and poly(methyl acrylate-b-styrene) (PMA-b-PS) block copolymers with three distinct molecular weights. Polyaniline (PANI) was synthesized by electrochemical method. Proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) have both been used to examine the properties of the polymers synthesized. In aqueous media at room temperature, PANI has been co-assembled with PS, PMA, and PMA-b-PS. The size and morphology of the co-assembled structures have been examined using transmission electron microscopy (TEM), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM). According to the findings, polymers hydrophobicity increased with increasing molecular weight, causing faster precipitation in aqueous solution and a reduction in particle size. The results demonstrated that adding conductive polymer produced core-shell morphologies, while the core morphologies are different. Thermodynamic principles governed morphology, and the most likely morphology to develop was the one that minimized the total surface free energy. The polymers caused the surface tension between the polymers with water and the surface tension between the primary polymer and the secondary polymer to be reduced by overlapping each other and precipitation.

In the present study, the thermal oxidation behaviour of high-density polyethylene (HDPE) containing each of two types of oxidized polyethylene (OPE), one prepared using 500 ppm of iron (III) stearate as pro-oxidant and the other without the pro-oxidant, was investigated. Fourier-transform infrared spectroscopy (FTIR) showed that the carbonyl index of the HDPE increased from 1.03 to 6.37 upon the addition of 5.0 wt.% of OPE containing the pro-oxidant after 100 h of thermo-oxidative aging at 90°C. Moreover, it was observed that the rate of changes in retained tensile strength and retained elongation-at-break of the HDPE during the thermal oxidation increased in the presence of 5.0 wt.% of each type of OPE, especially, the one containing iron (III) stearate, which was consistent with the obtained data from gel content measurements. Lastly, the evolution in crystallinity of the film samples was monitored by density measurements as well as differential scanning calorimetry (DSC). It was revealed that the crystallinity of the tested films during thermo-oxidative degradation grows faster in the presence of OPE. Overall, the findings indicated that the utilization of OPE containing trace amounts of iron (III) stearate can accelerate the thermal oxidation of HDPE films and facilitate entering the final biodegradation stage, while resolving the need to use high concentrations of harmful heavy metal salts.

The suitability of a polymer to be processed by injection molding is called moldability. The technicians in injection molding companies tend to estimate moldability by using a parameter named Melt Flow Index (MFI), which however can be often misleading since it represents the ability of a melt to flow in specific conditions, very different from the ones that the polymer encounters during injection molding. A much significant parameter is the so-called flow-length, which is the length reached by a polymer during injection molding in a thin cold cavity. In this work, three commercial grades of polypropylene were injection molded in a cold thin cavity and the flowlengths were measured in function of injection pressure and temperature. The results obtained were correlated with the rheological parameters. The results demonstrate that the MFI is misleading as a technical parameter for the moldability of polypropylene. An empirical equation is proposed to describe the flow-length of polypropylene in function of injection pressure.

In this particular study, shear stability, pour point temperature and cold cranking simulation viscosity of different poly (alkyl methacrylate) homopolymers were investigated. The successful synthesis of the homopolymers was verified using FTIR and 1H NMR spectroscopy. From the experimental results, it was perceived that shear stability and low-temperature performance of the modified oil are strongly dependent on alkyl length and synthesis reaction conditions. Higher shear stability was observed for the samples possessing shorter alkyl chain lengths. An increase in initiator concentration and reaction temperature led to a decrease in molecular weight and an increase in shear stability. Moreover, poly(alkyl methacrylate) homopolymers containing longer alkyl chain lengths represented better influence in the reduction of the size and cohesiveness of the crystal structure of paraffin wax. The results also revealed that the synthesized homopolymers with lower molecular weight play a greater performance in controlling friction at low temperatures.

The automotive industry has a significant need for composites made of high impact strength polymer blends. Melt-mixing was used in this work to reinforce hollow glass microspheres (HGMs) with 50:50 polypropylene/ polyamide 6 (PP/PA6) blends. Using FTIR spectroscopy, it is observed that the 50PP50PA6 blend is compatibilized with maleated PP, producing a reactively compatible blend. The compatibilization process has refined the morphology of the 50PP50PA6 blend. Additionally, the incorporation of HGMs into the 50PP50PA6 blend produced a finer blend morphology, which helped to enhance the crystallinity of the polymer phase and mechanical properties to the maximum. The tensile modulus and impact strength of a 50PP50PA6 blend with maleated PP that contains 3 wt.% HGMs are better than those of a neat blend by 15.6% and 90.1%, respectively. Fractography was used to identify the fracture mechanism which reveals the retention of droplets over the surface of impact specimens of HGMs-filled compatibilized PP/PA6 blend. When 50PP50PA6 blend with and without maleated PP is filled with HGMs, rheological characterization shows that the blend viscosity has decreased, indicating improved processability. Dynamic mechanical analysis (DMA) revealed that the incorporation of HGMs into the 50PP50PA6 blend enhances the storage modulus.