High Density Polyethylene Blends Research Articles

Melt-crystallization and self-nucleation of UHMWPE/bi-HDPE blends: The combined role of composition and molecular weight

Blends of bi-modal high-density polyethylene (bi-HDPE) and ultra-high molecular weight polyethylene (UHMWPE) with varying content (0–30 wt%.) and different molecular weights (MWs) (2.2, 3.5, and 4.5 M g/mol) of UHMWPE were prepared. The effect of UHMWPE content, MW, and their interplay on the microstructure, nucleation, and crystallization behavior of bi-HDPE was examined through rheology, scanning electron microscopy, and differential scanning calorimetry. The results revealed that UHMWPE serves as a partially miscible nucleating agent, effectively dispersing in the bi-HDPE matrix up to 5 wt%, thereby promoting the transition from randomly dispersed lamellae to a spherulitic morphology. The nucleating effect saturated when the UHMWPE content reached 10 wt%, leading to a diminished spherulitic structure. Beyond 10 wt% of UHMWPE, an anti-nucleation effect with segregated crystalline regions emerged. Isothermal kinetics analysis also revealed the highest crystallization rate at the optimum UHMWPE content of 5 wt%, where the critical nucleation energy barrier and fold-surface free energy were minimized. Apart from the UHMWPE content, signs of nucleation enhancement were slightly more pronounced in the bi-HDPE blend with the lowest molecular weight of UHMWPE. This phenomenon results from increased concentration fluctuations due to the larger interfacial area, as postulated from entanglement density measurements. For the first time, self-nucleation (SN) analysis revealed that the incorporation of 5 wt% of UHMWPE into bi-HDPE resulted in a wider Domain II width, indicating an increased memory effect. Notably, the crystalline memory was more pronounced in the blend containing UHMWPE with the MW of 2.2 M g/mol, exhibiting the super-nucleating effect with the highest nucleation efficiency of 218 %.

Morphological analysis of mechanically recycled blends of high density polyethylene and polypropylene with strong difference in melt flow index

Polyolefin (PO) blends are difficult to separate due to density and chemical structure similarities. The associated waste treatment in the context of mechanical recycling is therefore complicated by the establishment of multi-phase morphologies that are not yet fully understood. In the present work, a high density polyethylene (HDPE) with a very high melt flow index (MFI) and a polypropylene (PP) with a very low MFI are deliberately mingled to better understand the full spectrum of morphological variations for PO blending. The linkage with the control over injection mold-based mechanical properties such as tensile strength, elasticity modulus, elongation at break, and impact strength is made. This is done supported by the connecting of experimental analyses at different scales, including (i) the molecular scale via size exclusion chromatography and Fourier transform infrared spectroscopy (FTIR), and (ii) the meso-scale via scanning electron and polarized light microscopy as well as differential scanning calorimetry, including a differentiation between the bulk and surface region. Emphasis is both on blends processed once and re-processed either once, twice or three times. For the single processing, it is demonstrated that in most cases a droplet morphology is obtained, with smaller droplets in case HDPE is the minor component and with a dominance of HDPE at the surface even for 60% PP, due to a better HDPE flowability. It is further shown that the scission of PP chains and crosslinking of HDPE chains respectively facilitates and inhibits crystallization, at least if meso-scale -mixing as more evident during re-processing is not taking over. It is also highlighted that the properties of PP can be enhanced by adding up to 10 wt% HDPE, acting as a filler, and that the (ideally) reprocessed blends remain suitable for application.

The Effect of Processing Conditions on the Microstructure of Homopolymer High-Density Polyethylene Blends: A Multivariate Approach.

In this work, a multivariate approach was utilized for gaining some insights into the processing-structure-properties relationships in polyethylene-based blends. In particular, two high-density polyethylenes (HDPEs) with different molecular weights were melt-compounded using a twin-screw extruder, and the effects of the screw speed, processing temperature and composition on the microstructure of the blends were evaluated based on a Design of Experiment-multilinear regression (DoE-MLR) approach. The results of the thermal characterization, interpreted trough the MLR (multilinear regression) response surfaces, demonstrated that the composition of the blends and the screw rotation speed are the two most important parameters in determining the crystallinity of the materials. Furthermore, the rheological data were examined using a Principal Component Analysis (PCA) multivariate approach, highlighting also in this case the most prominent effect of the weight ratio of the two base polymers and the screw rotation speed.

Investigation of the influence of mineral fillers on the structural and mechanical characteristics of polyethylene high-density (PEHD) composites reinforced with alumina and talc

This study explores the impact of incorporating a blend of alumina and talc, ranging from 1 to 7%, into high-density polyethylene (HDPE) to modify its structural, rheological, and mechanical properties. Comparative evaluations with HDPE/Alumina and HDPE/Talc composites were conducted. The dual-filler combination was achieved through dry grinding, followed by melt processing with a Brabender plastograph. FTIR spectroscopy analysis of HDPE/ (alumina + talc) composites revealed interactions between aluminum and oxygen, with a peak at 700 cm-1 indicating alumina integration into the HDPE matrix, influencing composite properties. Impact strength decreased with talc inclusion but significantly improved with alumina. Notably, a 5% blend of HDPE/(alumina-talc) fillers exhibited the highest impact resistance. Tensile stress showed peaks at 1% talc content and a 3% filler mixture, emphasizing synergistic effects and talc's superiority over alumina. Synergism in elongation at break was observed for HDPE/ (alumina + talc) composites. Additionally, HDPE/Alumina composites displayed the highest modulus of elasticity, while HDPE/(Alumina + Talc) composites had the highest melt flow index. Surface treatments promoted uniform filler dispersion within the HDPE matrix, enhancing mechanical properties. Overall, composites with binary fillers harnessed synergistic effects, combining advantages from both components

Identification of Plastics in Mixtures and Blends through Pyrolysis-Gas Chromatography/Mass Spectrometry.

In this paper, the possibility of detecting polymers in plastic mixtures and extruded blends has been investigated. Pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) allows researchers to identify multicomponent mixtures and low amounts of polymers without high spatial resolution, background noise and constituents mix interfering, as with molecular spectrometry techniques normally used for this purpose, such as Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy and differential scanning calorimetry (DSC). In total, 15 solid mixtures of low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyamide (PA) and polycarbonate (PC) in various combinations have been qualitatively analyzed after choosing their characteristic pyrolysis products and each polymer has been detected in every mix; thus, in extruded blends of high-density polyethylene (HDPE), PP and PS had varying weight percentages of the individual constituents ranging from 10 up to 90. Moreover, quantitative analysis of these polymers has been achieved in every blend with a trend that can be considered linear with coefficients of determination higher than 0.9, even though the limits of quantification are lower with respect to the ones reported in the literature, probably due to the extrusion process.

Modifications of Phase Morphology, Physical Properties, and Burning Anti-Dripping Performance of Compatibilized Poly(butylene succinate)/High-Density Polyethylene Blend by Adding Nanofillers.

A twin-screw extruder was used to fabricate poly(butylene succinate) (PBS)/high-density polyethylene (HDPE) blends (7:3 weight ratio) and blend-based nanocomposites. Carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and organoclays (15A and 30B) served as the nanofiller, while maleated HDPE (PEgMA) acted as an efficient compatibilizer for the blend. In the composites, individual nanofillers were mostly localized in HDPE domains, but some fillers were also observed at PBS-HDPE interfaces. The sea-island morphology of the compatibilized blend evolved into a pseudo-co-continuous morphology in the composites. Differential scanning calorimetry results confirmed that PEgMA with HDPE evidently accelerated the crystallization of PBS in the blend. The possible nucleation effect of added fillers on PBS crystallization was obscured by the formation of quasi-connected HDPE domains, causing fewer PBS nucleation sites. The presence of nanofillers improved the thermal stability and burning anti-dripping behavior of the parent blend. The anti-dripping efficiency of added fillers followed the sequence CNT > 15A > 30B > GNP. The rigidity of the blend was increased after the formation of nanocomposites. In particular, adding GNP resulted in 19% and 31% increases in the Young's modulus and flexural modulus, respectively. The development of a pseudo-network structure in the composites was confirmed by measurement of rheological properties. The electrical resistivity of the blend was reduced by more than six orders of magnitude at 3 phr CNT loading, demonstrating the achievement of double percolation morphology.

Thermomechanical Properties of Virgin and Recycled Polypropylene-High-Density Polyethylene Blends.

This paper provides evidence and discusses the variability in the thermomechanical behaviour of virgin and recycled polypropylene/high-density polyethylene blends without the addition of other components, which is sparse in the literature. Understanding the performance variability in recycled polymer blends is of critical importance in order to facilitate the re-entering of recycled materials to the consumer market and, thus, contribute towards a circular economy. This is an area that requires further research due to the inhomogeneity of recycled materials. Therefore, the thermal and mechanical properties of virgin and recycled polypropylene/high-density polyethylene blends were investigated systematically. Differential scanning calorimetry concludes that both the recycled and virgin blends are immiscible. Generally, recycled blends have lower overall crystallinity and melting temperatures compared with virgin blends while, remarkably, their crystallisation temperatures are compared favourably. Dynamical mechanical analysis showed little variation in the storage modulus of recycled and virgin blends. However, the alpha and beta relaxation temperatures are lower in recycled blends due to structural deterioration. Deterioration in the thermal and mechanical properties of recycled blends is thought to be caused by the presence of contaminants and structural degradation during reprocessing, resulting in shorter polymeric chains and the formation of imperfect crystallites. The tensile properties of recycled blends are also affected by the recycling process. The Young's modulus and yield strength of the recycled blends are inferior to those of virgin blends due to the deterioration during the recycling process. However, the elongation at break of the recycled blends is higher compared with the virgin blends, possibly due to the plasticity effect of the low-molecular-weight chain fragments.

Morphology and Mechanical Properties of High Density Polyethylene and Ethylene-Methyl Acrylate Copolymer Blends with Organoclay

In this research, the effect of ethylene-methyl acrylate copolymer (EMAC or EMAC30) and clay surface modified with aminopropyltriethoxysilane 0.5-5 wt% and octadecylamine 15-35 wt% (Clay-ASO) on the morphological, mechanical, and thermal properties of high density polyethylene (HDPE) were investigated. The polymer blends and composites were prepared by an internal mixer and then samples were molded by compression molding. The morphology analysis showed that the presence of fibrous surface at the specimen fracture surface of HDPE/EMAC30 blends. The phase morphology of HDPE blends with Clay-ASO 3, 5 and 7 phr was observed the phase separation of EMAC30 and aggregate of Clay-ASO at high EMAC30 content. Young’s modulus of HDPE/Clay-ASO composites increased with increasing Clay-ASO composites. The presence of Clay-ASO did not improve Young’s modulus and tensile strength of HDPE/EMAC30/Clay-ASO composites. The strain at break of HDPE/EMAC30 blends increased with increasing EMAC30 content. The incorporation of EMAC30 and Clay-ASO had no effect on the melting temperature of HDPE blends and composites, respectively. The percent crystallinity of HDPE/EMAC30 and HDPE/EMAC30/Clay-ASO was lower than that of pure HDPE. The addition of EMAC30 and Clay-ASO decreased the degradation temperatures of HDPE/EMAC30 blends and composites.

Plastic Waste Valorization for Fused Deposition Modeling Feedstock: A Case Study on Recycled Polyethylene Terephthalate/High-Density Polyethylene Sustainability

In this study, material development, characterization, and sustainability assessment are performed on blends from recycled post-consumer commodity plastics for fused deposition modeling (FDM) filament extrusion. A recycled polyethylene terephthalate (rPET) and high-density polyethylene (rHDPE) blend 80:20 ratio is modified using three different methods: compatibilization with Maleic Anhydride, surface functionalization of PET with sodium dodecyl sulphate (SDS), and hybridization by combination of the two methods which is a novel approach. The selected blends were reinforced with chopped glass fibers and characterized. The printability of blends was assessed, and the dimensional accuracy of the prints was calculated. In addition, a cost estimation and comparison between the developed blends and the commercially available FDM filaments was carried out. Finally, life cycle assessment (LCA) was conducted for each prepared blend to facilitate the decision of the optimum blend in relation to mechanical properties and environmental performance and hence correlate the material, economic, and sustainability advantages.

Dynamic structure transformation of char precursors during co-pyrolysis of coal and HDPE by using ReaxFF MD simulation and experiments

Understanding the effects of co-pyrolysis synergies between low-rank coal and high-density polyethylene (HDPE) on the carbon structure evolution in char and the relationship between char structure and chemical bonds evolution is very needed. A combination of ReaxFF MD and experimental approaches provides an opportunity for fully understanding the dynamic profiles of char structures and coking trends during co-pyrolysis process of coal and HDPE. In this work, consistent conclusions were obtained from fixed-bed experiments and ReaxFF MD simulations in product distribution during both individual coal pyrolysis and co-pyrolysis at different temperatures. The ReaxFF MD simulation results reveal that adding HDPE partially inhibited the coking process of coal char. The RDF results indicated higher order degree and aromaticity exist in coal/HDPE(7:3)-Char when compared to those in coal-Char, which agrees well with the findings from XRD and FTIR approaches. By analyzing the evolution of C=C, C=O, C-O, C(sp2)-C(sp3), C(sp3)-C(sp3) and C(sp2)-H bonds in C40+ fragments during secondary simulations of co-pyrolytic char, it was observed that the structural order and aromaticity of co-pyrolytic char increase with temperature, and the oxygen-containing bonds are the initial recombination sites for char formation. These findings provide rich theoretical information to complement the understanding of char structure in co-fed systems and the interaction between coal and HDPE blend.

High density polyethylene and butanol-gasoline blends: A material compatibility study

We are now well on the path of transitioning away from the fossil fuel resources on cutting down their consumption as much as possible. The fuels chosen for this study include ethanol-butanol (EB) -gasoline, acetone-butanol-ethanol (ABE) -gasoline and methanol-butanol (MB) -gasoline blends. High density polyethylene (HDPE) is a polymer that is extensively used in several auto parts and fuelling infrastructure materials. Incompatibility between these blends and fueling infrastructure system should be studied comprehensively for the adoption of these alternative fuels to be faster and hassle free. This study intends to gauge the changes in HDPE because of its immersion in the gasoline-alcohol blends mentioned for a period of 4, 30 & 90 days. The changes were ascertained by studying the mass, tensile strength, elongation, and hardness of the samples before and after immersion into blends. Sophisticated techniques were used to characterize the morphological and chemical changes of the polymer. The results showed that there was an increase in the mass of the HDPE samples as a result of the absorption of the blends by the polymeric samples. A decrease in tensile strength and hardness values were recorded for the samples whereas the elongation values were found to increase. Studies revealed that there was neither fuel degradation nor any oxidative degradation of the polymeric sample. The results indicated an increase in the mass and elongation of the HDPE as a result of the absorption of the fuel leads to lesser stable polymeric matrix and decrease in the percentage crystallinity. Hence this investigation led us to the conclusion that all the fuels blends studied are highly compatible with HDPE, even in instances where a change in the mechanical properties is seen, it is similar to that seen in gasoline.

Evaluation of the Mechanical, Thermal and Rheological Properties of Hop, Hemp and Wood Fiber Plastic Composites.

The aim of this study was to evaluate the use of waste natural fibers from milled hop bines and hemp stalks, without chemical treatment, and compare them to a commercial wood fiber for use in wood-plastic composite (WPC) materials. The fibers were characterized (density, fiber size and chemical composition). WPCs were produced by the extrusion of a blend of fibers (50%), high-density polyethylene (HDPE) and coupling agent (2%). The WPCs were characterized for their mechanical, rheological, thermal, viscoelastic and water resistance properties. Pine fiber was about half the size of hemp and hop fibers and thus had a higher surface area. The pine WPC melts had a higher viscosity than the other two WPCs. Additionally, the tensile and flexural strengths of the pine WPC were higher than those of hop and hemp WPCs. The pine WPC was also shown to have the least water absorption followed by hop and hemp WPCs. This study highlights that different lignocellulosic fibers influence their WPC properties. The properties of the hop- and hemp-based WPCs were comparable to commercial WPCs and can be improved by further milling/screening the fibers to a smaller particle size (volumetric mean of ~88 μm) to increase their surface area, fiber-matrix interactions and improve stress-transfer.

Ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blends with outstanding mechanical properties, wear resistance, and processability

Ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blends with outstanding mechanical properties, wear resistance, and processability

Additive Effects of Solid Paraffins on Mechanical Properties of High-Density Polyethylene

In this work, two types of solid paraffins (i.e., linear and branched) were added to high-density polyethylene (HDPE) to investigate their effects on the dynamic viscoelasticity and tensile properties of HDPE. The linear and branched paraffins exhibited high and low crystallizability, respectively. The spherulitic structure and crystalline lattice of HDPE are almost independent of the addition of these solid paraffins. The linear paraffin in the HDPE blends exhibited a melting point at 70 °C in addition to the melting point of HDPE, whereas the branched paraffins showed no melting point in the HDPE blend. Furthermore, the dynamic mechanical spectra of the HDPE/paraffin blends exhibited a novel relaxation between -50 °C and 0 °C, which was absent in HDPE. Adding linear paraffin toughened the stress-strain behavior of HDPE by forming crystallized domains in the HDPE matrix. In contrast, branched paraffins with lower crystallizability compared to linear paraffin softened the stress-strain behavior of HDPE by incorporating them into its amorphous layer. The mechanical properties of polyethylene-based polymeric materials were found to be controlled by selectively adding solid paraffins with different structural architectures and crystallinities.

Compatibilization of polypropylene/high‐density polyethylene blends using poly(propylene‐co‐ethylene)

AbstractTernary blends of polypropylene (PP), high‐density polyethylene (HDPE), and a random copolymer with 85% propylene and 15% ethylene (trade name Vistamaxx 6202, abbreviated here as VM) have been investigated to elucidate the efficiency of this additive in the management of recycling streams. Differential scanning calorimetry showed that VM will induce simultaneous crystallization of PP and HDPE. Polarized Optical Microscopy revealed a breakdown in the spherulitic structure already at 10% of additive (for blends with ratio PP: HDPE = 1:1), respectively 17%, (for PP/HDPE = 7:3). A similar threshold was found in the impact strength, and stress–strain‐curves. This means that VM is also advantageous for recycling of PP: HDPE blends, especially those with high PP content.

Influence of high-density polyethylene content on the rheology, crystal structure, and mechanical properties of melt spun ultra-high-molecular weight polyethylene/high-density polyethylene blend fibers

High-density polyethylene (HDPE) content significantly influences the structure and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE)/HDPE blend fibers. The molecular chain disentanglement and crystallization characteristics of as-spun filaments and fibers and how the structure affects the final mechanical properties of the fibers were thoroughly studied by adding different contents of HDPE. Dynamic mechanical analysis (DMA) and rheological analysis indicated that the molecular entanglement decreased with increasing HDPE content, improving the UHMWPE melt processability. Sound velocity orientation (SVO) studies indicated that the UHMWPE/HDPE as-spun filaments and fibers with an HDPE content of 40 wt% (U6H4) had a higher molecular chain orientation level. Furthermore, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses indicated that U6H4 had the highest crystallinity and the thinnest grains in the axial direction, respectively. The compact crystal structure and fully stretched molecular chains of U6H4 yielded the best mechanical properties. The present work disclosed the effect mechanism of HDPE contents on the preparation and properties of UHMWPE/HDPE fibers, which provided an effective and universal strategy for manufacturing high-strength UHMWPE/HDPE fibers with the melt spinning method.

Effect of Nano-SiO2 on Different Stages of UHMWPE/HDPE Fiber Preparation via Melt Spinning

Ultra-high molecular weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blend with lower viscosity is more suitable for melt spinning compared to pure UHMWPE; however, the mechanical property of the blend fiber is hard to dramatically improve (the maximum tensile strength of 998.27 MPa). Herein, different content modified-nano-SiO2 is incorporated to UHMWPE/HDPE blend fiber. After adding 0.5 wt% nano-SiO2, the tensile strength and initial modulus of UHMWPE/HDPE/nano-SiO2 fiber are increased to 1211 MPa and 12.81 GPa, respectively, 21.57% and 43.32% higher than that of UHMWPE/HDPE fiber. Meanwhile, the influence of the nano-SiO2 content on the performance for as-spun filament and fiber are emphatically analyzed. The crystallinity and molecular chain orientation of as-spun filament reduces with the addition of nano-SiO2. On the contrary, for fiber, the addition of nano-SiO2 promoted the crystallinity, molecular chain orientation and grain refinement more obvious at a lower content. Furthermore, the possible action mechanism of nano-SiO2 in the as-spun filament extrusion and fiber hot drawing stage is explained.

Crystallization Kinetics in an Immiscible Polyolefin Blend.

Motivated by the problem of brittle mechanical behavior in recycled blends of high density polyethylene (HDPE) and isotactic polypropylene (iPP), we employ optical microscopy, rheo-Raman, and differential scanning calorimetry (DSC) to measure the composition dependence of their crystallization kinetics. Raman spectra are analyzed via multivariate curve resolution with alternating least-squares (MCR-ALS) to provide component crystallization values. We find that iPP crystallization behavior varies strongly with blend composition. Optical microscopy shows that three crystallization kinetic regimes correspond to three underlying two-phase morphologies: HDPE droplets in iPP, the inverse, and cocontinuous structures. In the HDPE droplet regime, iPP crystallization temperature decreases sharply with increasing HDPE composition. For cocontinuous morphologies, iPP crystallization is delayed, but the onset temperature changes little with the exact blend composition. In the iPP droplet regime, the two components crystallize nearly concurrently. Rheological measurements are consistent with these observations. DSC indicates that the enthalpy of crystallization of the blends is less than the weighted values of the individual components, providing a possible clue for the decreased iPP crystallization temperatures.

Evaluation of the Role of Ethylene Vinyl Acetate on the Thermo-Mechanical Properties of PET/HDPE Blends

In this paper, blends of recycled polyethylene terephthalate (r-PET) and high-density polyethylene (HDPE) with and without a compatibilizer were prepared using a Brabender Haake Rheocord at 270°C and 32rpm. Ethylene vinyl acetate was chosen as the compatibilizer and its proportion was set to 5, 7, and 10 wt%. The thermal properties and crystallization behavior were determined by Differential Scanning Calorimetry (DSC). Micromechanical properties were also investigated using a Vickers microindentation tester. The DSC analysis indicates that the melting temperature of r-PET and HDPE in all the blends, compatibilized and uncompatibilized, remains constant and almost the same as those of the pure component. On the other hand, it is shown that the degree of crystallinity of HDPE in the blends calculated by DSC depends on the composition of the polymeric mixture. However, the Hardness (H) decreases with increasing r-PET content until 50/50 composition of r-PET/HDPE is reached, whereas for larger r-PET content values, H increases. The same trend was obtained with the addition of the compatibilizer.

Thermal degradation and thermal kinetic of SEBS block copolymer compatibilized PS/HDPE blends

The effect of styrene-ethylene/butylene-styrene block copolymer (SEBS) on the thermal degradation of polystyrene (PS)/high density polyethylene (HDPE) blends have been investigated. Polystyrene and (HDPE) are widely used thermoplastics, which have extensive application in everyday life. The main disadvantage of PS/PE systems is their poor miscibility which can be improved by adding compatibilizer. The blends were prepared by melt mixing in a twin screw extruder Haake Record 90. The behavior of the thermal degradation of PS/HDPE and PS/HDPE/SEBS blends has been investigated in inert nitrogen atmosphere by using thermogravimetric analysis (TGA) to obtain the degradation temperature and activation energy ( E a). The Ea for the PS/HDPE blends as well as for the PS/HDPE/SEBS blends was determined by the isoconversional Kissinger–Akahira–Sunose (KAS) method. The results indicated that the HDPE enhance thermal properties of the blends. The addition of SEBS in PS/HDPE blends increased the E a in all blends.