High-density Polyethylene Melt Research Articles

Thermoformed products from high-density polyethylene and Softwood kraft pulp.

Plastic recycling, waste minimization such as process outfall valorization promotes a circular economy. Herein, food trays have been produced in the moulded pulp thermoforming process. To this end, high-density polyethylene (HDPE) outfall has been dispersed in water via Poly vinyl alcohol (PVA) addition in a Northern Bleached Softwood KraftPulp (NBSKP) slurry. Samples physical and mechanical properties have been evaluated. With an increasing HDPE content, parts air permeability was drastically reduced to a minimum of 2.4±0.8 mL min-1. In addition, water and grease hold out properties have been increased with minimum waterCobb1800 value of 10.9±5.4 gm-2 and oil Cobb1800 value of13.18±6.5 gm-2. Samples with high HDPE content demonstrated hydrophobic surface with water contact angle value above 90°. HDPE melting and binding to wood pulp fibers was monitored by SEM images. Regarding the mechanical properties, HDPE induced plastic deformation with a reduced Young modulus by 17 %. Moreover, the addition of HDPE increased wet strength by 81 %. However, the produced foodtray composites with high HDPE content demonstrated low repulpability index.

Modeling the matching stage of HDPE hot plate welding: A study using regression and support vector machine models

AbstractThis research studies the material displacement of high‐density polyethylene (HDPE) during the initial stage of the hot plate welding (HPW) process, called the Matching stage. Newly developed mathematical models simulate the relationship between the main process parameters (force, temperature, and time) and the size of the surface area. The collected data was used to develop four mathematical models for material displacement and time. Two models are machine learning based models (support vector machines). The other two models are regression models in the form of functions. In addition, this study provides a visual representation of HDPE melt displacement with the changes in temperature and pressure. The obtained results indicate that these models can be used for developing a parameter adjustment process or determining specifications for new production equipment. The potential applications of the developed models can be extended to industries that use HPW of HDPE, such as automotive or aerospace. This could result in significant savings in the amount of scrap and waste due to inaccurate and ad hoc settings that currently take place in the industry.Highlights Study of HDPE material displacement in the hot plate welding Matching stage. Visualization of HDPE melt displacement with temperature and pressure changes. Development of SVM and mathematical regression models. Applications in parameter adjustment and equipment specification. Savings in scrap and waste by reducing inaccurate settings.

Neural virtual sensor for determination of high-density polyethylene melt flow index and solids concentration in a loop slurry reactor

Neural virtual sensor for determination of high-density polyethylene melt flow index and solids concentration in a loop slurry reactor

Predicting High-Density Polyethylene Melt Rheology Using a Multimode Tube Model Derived Using Non-Equilibrium Thermodynamics.

Based on the Generalized bracket, or Beris-Edwards, formalism of non-equilibrium thermodynamics, we recently proposed a new differential constitutive model for the rheological study of entangled polymer melts and solutions. It amended the shortcomings of a previous model that was too strict regarding the values of the convective constraint release parameter for the model not to violate the second law of thermodynamics, and it has been shown capable of predicting a transient stress undershoot (following the overshoot) at high shear rates. In this study, we wish to further examine this model's capability to predict the rheological response of industrial polymer systems by extending it to its multiple-mode version. The comparison with industrial rheological data (High-Density Polyethylene resins), which was based on comparison with experimental data available in (a) Small Amplitude Oscillatory shear, (b) start-up shear, and (c) start-up uniaxial elongation, was noted to be good.

Fabric Insert Injection Molding for the Preparation of Ultra-High Molecular Weight Polyethylene/High-Density Polyethylene Two-Component Self-Reinforced Composites.

The fabric insert injection molding approach can be applied to produce easily recyclable self-reinforced polymer composites (SrCs) whose reinforcement and matrix are from the same polymer. However, the mechanical properties of the SrCs are usually limited due to the poor impregnation of the inserted fabric. In this work, the ultra-high molecular weight polyethylene (UHMWPE) fabrics were used as the insert, and the high-density polyethylene (HDPE) melt was injected to fill the mold cavity and impregnate the fabrics. The UHMWPE/HDPE two-component SrCs were prepared. The large difference of melting temperatures between UHMWPE and HDPE can establish a wide processing temperature window, and thus the impregnation of the fabric can be improved by increasing temperature. The tensile strength and modulus of the UHMWPE/HDPE SrCs were up to 148 and 1132 MPa, respectively. The peel strength could be up to 35.2 N/cm. The influences of four main injection molding parameters, including the injection temperature, injection pressure/packing pressure, injection velocity, and packing time, were investigated. The temperature, pressure, viscosity, and density of the matrix in the mold cavity were calculated by the numerical simulation to indicate the impregnation process during the fabric insert injection molding process.

Effects of shear stress on the behavior of volatile bubbles in the high‐density polyethylene melt

AbstractA novel visualization system, in which polymer melt is sheared by a sliding plate, was established to simulate different pressure shear zones of the screw extruder. In this work, the nucleation, growth, coalescence, and breakup of n‐hexane bubbles in the high‐density polyethylene (HDPE) melt under shear stress were observed through a high‐speed camera. It was found that the nucleation rate of bubbles in the HDPE melt increased with the shear rate. Moreover, the bubble diameter at high‐pressure shear zones decreased with time until bubbles disappeared but increased with time at low‐pressure shear zones. A modified prediction model of bubble coalescence time at high‐pressure shear zones was established, and the relative deviation was less than 1%. Three bubble breakup modes, that is, tensile breakup, erosive breakup, and breakup at the gas–liquid interface, were observed under shear. Finally, a new mechanism of foam devolatilization in the screw extruder was proposed.

Effects of diluent content on the crystallization behavior and morphology of polyethylene membrane fabricated via thermally induced phase separation process

Thermally induced phase separation technique has been widely applied to produce various commercial high-density polyethylene (HDPE) membranes based on the HDPE/diluent system. In this work, the crystallization behavior and morphological evolution of HDPE/liquid paraffin (LP) blends were systematically investigated by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), two-dimensional small-angle X-ray scattering (2D-SAXS) and scanning electron microscope (SEM). It is found that the chain mobility of HDPE is promoted and the entanglement density reduces with the introduction of diluent LP. When the LP content is lower than 40%, the liquid diluent distributes randomly in HDPE melt, while as the LP content exceeds 40%, the diluent saturates the inter-molecular space of HDPE, resulting in the full growth of lateral lamellar dimension of PE crystal. On the other hand, the morphologies of HDPE/LP films change considerably with the diluent content. (1) LP content <20%: diluent lives directly in the inter-lamellar region; (2) 20% ≤ LP content ≤40%: diluent will be excluded into the inter-cluster region and leads to the formation of separated LP domains between PE clusters. (3) LP content >40%: diluent will be aggregated between the stacked clusters to create numerous interconnected LP domains which act as the pathways for the gas or liquid permeation after the removal of LP. Accordingly, we provide a new guidance for the condensed structure controlling and the development of PE membranes with diverse functionalities.

Thermal and Crystallization Behaviour of Polyphenylene Sulfide in Engineering Polymer Blends with HDPE

Abstract The thermal and crystallization behaviour of polyphenylene sulfide (PPS) in its blends with high density polyethylene (HDPE) is reported. Three grades of HDPE ranging in MFI from 0.4 to 52 were used in the investigation. The effect of composition and molecular weight of HDPE on the crystallization process and morphology of PPS in the blends has been investigated by the technique of Differential Scanning Calorimetry (DSC). In the blends, PPS crystallizes in presence of molten HDPE. It is observed that the morphology of PPS in terms of crystallite size and crystallite size distribution in the blends is significantly affected by blending with HDPE. The temperature onset of melting was found to increase with increasing HDPE content and the melting peak width was found to decrease with increasing HDPE content. This indicates a larger crystallite size and a narrower crystallite size distribution of PPS in blends. The effect is more pronounced in HDPE-rich compositions. The extent of the variation in the temperature onset of melting and peak width were comparable for all the grades of HDPE. The degree of crystallinity of PPS in the blends is reduced significantly (55–70%) in HDPE-rich blends. Therefore, it is concluded that the crystallization of PPS is affected by the presence of HDPE melt. The crystallization scans of PPS in the blends, obtained in the cooling mode, did not show any evidence of accelerated nucleation. On the other hand, a marginal reduction in the temperature onset of crystallization was observed. The temperature range of crystallization of PPS in the blends was found to be less for all compositions except for 90/10 (PPS/HDPE). In summary it is concluded that blending of HDPE with PPS influences the crystal growth of PPS significantly although the effect on its homogeneous nucleation is also considerable. As a result, the morphology of PPS crystallized in blends is different from that of the homopolymer. The changes in the morphology of PPS are not sensitive to the molecular weight of HDPE probably because of the high temperature of PPS crystallization relative to the melting point of HDPE.

Zero Shear Viscosity and Steady State Shear Creep Compliance of Industrial High Density Polyethylene Melts using the Meissner’s Procedure－The Linearity and the Dependence on Molecular Weight and its Distribution

Zero Shear Viscosity and Steady State Shear Creep Compliance of Industrial High Density Polyethylene Melts using the Meissner’s Procedure－The Linearity and the Dependence on Molecular Weight and its Distribution

Development of Leather Cutting Board from Plastic Waste

Cutting is the process in which goods or garment material are cut and converted into pattern shapes of the goods or garment components. There are two methods of Leather cutting, which are hand cutting and machine cutting. Hand cutting is done with the use of hand knife, cutting board and cutting patterns. Machine cutting can be done using semi-automatic cutting machines or fully-automatic cutting machines. Currently, in Ethiopia, different local and foreign investors are participating in leather products manufacturing. Most of the leather product manufacturing industry and some Small and Medium enterprise’s (SME’s) in the country are using leather cutting machines in order to cut leather goods or garment parts. Most of the industry and SMEs are using imported cutting board made of plastics and rubbers. However, these cutting boards are expensive.&#x0D; &#x0D; This research aimed at developing a cutting board made from HDPE (High-Density Polyethylene) plastic waste as main material, calcium carbonate as a filler and glass fiber as a reinforcing material. Primary and secondary data gathering techniques were applied simultaneously. Primary data were collected through interview and field observation. Secondary data was gathered by reviewing different literature. The cutting board developed through collecting HDPE plastic waste, washing, shredding and melting the shredded plastic with filler and reinforcing material. The melted plastic poured in to cutting board mold and cooled. The developed cutting board was compared with HDPE cutting board available in the local market. The developed board showed relative compression and hardness properties with the HDPE cutting board available in the market. In the cost analysis, the developed cutting board is cheaper than the cutting board which available in the market. However, the cutting board in the market has better surface texture and quality than the developed cutting board. Melting HDPE plastic waste using metal or clay cooking pots and charcoal fire is a tedious task and smoke from the fire will cause human health problem and will affect environment. Consequently, manual plastic melting method is not feasible for mass production, because it is difficult to control the amount of heat (charcoal fire) during melting process. Based on this the authors recommend using machine based plastic melting and molding during HDPE and related plastic recycling.

Modelling of Elongational Flow of HDPE Melts by Hierarchical Multi-Mode Molecular Stress Function Model.

The transient elongational data set obtained by filament-stretching rheometry of four commercial high-density polyethylene (HDPE) melts with different molecular characteristics was reported by Morelly and Alvarez [Rheologica Acta 59, 797–807 (2020)]. We use the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model of Narimissa and Wagner [Rheol. Acta 54, 779–791 (2015), and J. Rheology 60, 625–636 (2016)] for linear and long-chain branched (LCB) polymer melts to analyze the extensional rheological behavior of the four HDPEs with different polydispersity and long-chain branching content. Model predictions based solely on the linear-viscoelastic spectrum and a single nonlinear parameter, the dilution modulus for extensional flows reveals good agreement with elongational stress growth data. The relationship of dilution modulus to molecular characteristics (e.g., polydispersity index (PDI), long-chain branching index (LCBI), disengagement time ) of the high-density polyethylene melts are presented in this paper. A new measure of the maximum strain hardening factor (MSHF) is proposed, which allows separation of the effects of orientation and chain stretching.

Melting and Crystallization of High-Density Polyethylene Mixed with Organic Acids and Acid–Base Indicators after Plastic Deformation at High Pressures

Melting and Crystallization of High-Density Polyethylene Mixed with Organic Acids and Acid–Base Indicators after Plastic Deformation at High Pressures

Production of Hollow Block Using Waste Plastic and Sand

In building construction, hollow concrete block (HCB) is a versatile material used in the construction industry, consisting of a mixture of cement, sand, and optionally fine aggregates with water. The cost of these materials, which make up the concrete block, is expensive. So we should use a renewable natural resource that causes negative impacts on the environment. Plastics are one of the materials present in our everyday lives, which have many chemical and hazardous substances that affect human health and the surrounding environment. This study aims to produce hollow blocks using waste plastic material in the ratio of 1:2, 1:3, 1:4, and 1:5 of hollow block size 40cm X 20cm X 10cm of different Polyethylene Terephthalate (PET) and High-Density Polyethylene (HDPE) waste plastic and sand content. This research discussed the material used, the methodology was followed, and the production of hollow blocks and Quality control test of prepared material samples compared with the standard material specification. In this research work, many characteristics that have relevance to the production of Hollow blocks were considered. The plastic is shredded, washed, dried, and melted within the range of 257-315°C temperature in open-air. After melting of PET and HDPE into liquid-state, fixing the sand materials' proportion, mixing the sand materials fed into the mold, and testing the samples after 48 hours was conducted. The test results notice that properties of two samples produced from hollow block satisfy the class-B based on Ethiopian Building Code Standard requirements. The test result for the 1:2 ratio having 3.87Mpa. Therefore, the hollow block production has high compressive strength and low water absorption, which fulfills the standard requirement comparing with the surface property of HCB and aesthetics. The rough surface of HB creates bondage with mortar, which is easier for plastering purpose.

Саlculation of heat transfer processes at canlendering of polyethylene sheets

Introduction. The technological limitations of the calendering process include the condition of leaving the sheet from the calender in the presence of a middle layer of melt, or a sufficient value of the average temperature of the sheet, which determines the flatness of the sheet with subsequent cooling and glazing in a flat state on the roller conveyor. The process of vitrification of the polymer melt has a wide temperature range, which greatly complicates the calculations.Materials and methods. Processing of high density polyethylene (HDPE) on a calender with three rolls is considered. A series of numerical experiments was performed.Results and discussion. Boundary conditions for the mathematical model of sheet cooling and conditions for numerical integration of the equation of nonstationary thermal conductivity taking into account the heat of crystallization are formulated, the equation is presented in finite differences, using a grid with a step along the sheet length.The letter from HDPE in the physical model is conditionally expanded, the following assumptions are made:1. the thickness of the sheet is much smaller than the diameter of the shafts of the calender, so the orthogonal coordinate system is used;2. the transition of the melt from the initial thickness of the workpiece to the final occurs at the same linear velocity (the melt does not slip on the shaft);3. the thermal conductivity of HDPE is much less than the thermal conductivity of the shaft material, so the temperature of the sheet at the point of contact with the shaft is equal to the temperature of the shaft;4. reduction of sheet thickness in the second gap does not occur;5. energy dissipation in the gaps does not affect the temperature fields in the melt;6. heat transfer along the sheet due to thermal conductivity is absent;7. the width of the sheet is much larger than the thickness, so the model of the cooling process is simplified to one-dimensional, without heat transfer across the sheet.For the surface of the sheet, which is cooled by air by free convection, the method of control volume (heat balance method) was used for the boundary layer with a thickness of half a step of the grid along the thickness of the sheet.Numerical experiments were performed for the following conditions: HDPE performance 500 kg / h; initial melt temperature 235°C; diameter of calender shafts 0,25 m; sheet thickness 1.0; 2.0; 3.0; 5.0 mm. Sheet width 1.0 m. The temperature of the first shaft 125°С, shaft temperatures №2 and №3 were selected under the condition of the average melt temperature at the outlet of the calender 125°С, ambient air temperature 20°С, heat transfer coefficient from the sheet and the shaft to air 25 W / (m2K).An example of the results of numerical integration by the Runge – Kutta method (temperature fields and average melt temperature) is shown in the figures.The theoretical analysis of heat exchange processes during calendering of sheets from high density polyethylene melt is carried out, the technological parameters of calendering and their influence on the main quality parameters are analyzed.For the conditions of the numerical experiment, it was found that when calendering sheets with HDPE with a thickness of 1.0 to 2.0 mm will have to choose a high-temperature coolant, which greatly complicates the system of thermal stabilization of the shafts. A 1 mm thick sheet will not have gloss due to the high temperature of the shafts, and the temperature inhomogeneity of the shaft surface due to the high heat flux density can lead to the formation of a central strip on the surface of the sheet without gloss. Calendering of sheets with HDPE with a thickness of 5 mm or more for the conditions of numerical experiment causes difficulties due to the possible "blasting" of the sheet up (behind the hot shaft).Conclusions. It is established that when calendering sheets of smaller thickness, the heat load on the middle shaft increases, and it may be necessary to use high-temperature coolants. The optimal temperature of the calender shafts is in a narrow range, so when designing new equipment, thermal calculation is important.

Effects of temperature on nucleation and collapse of volatile bubbles in the high density polyethylene melt

High density polyethylene/n-Hexane system was adopted to investigate the bubbles nucleation and collapse in polymer melt with a visualization apparatus at different temperatures. The results showed that the initial bubble number, initial total bubble volume and the mean bubble diameter all increased with the temperature increasing, and the bubble diameter distribution changed from single peak distribution to bimodal distribution. Moreover, the effect of temperature on the maximum bubble diameter was mainly reflected in the change of the pressure in bubbles due to the change of the volatile content in the polyethylene melt. For bubble collapse, the collapse time became longer but the bubble collapse rate became faster with the temperature increasing, and a fitting model was established in which the collapse coefficient n was used to describe the collapse rate. Through dimension analysis, the correlation between the collapse coefficient n and the melt surface tension σ, zero-shear melt viscosity η0, diffusion coefficient D, maximum bubble diameter dmax, melt density ρ, initial bubble number density Nini were established and the variation of D with temperature could be predicted as an exponential correlation.

Enhanced Reproducibility of Positive Temperature Coefficient Effect of CB/HDPE/PVDF Composites with the Addition of Ionic Liquid

Developing an effective method for improving the reproducibility of positive temperature coefficient (PTC) effect is of great significance for large-scale application of polymer based PTC composites, owing to its contribution to the security and reliability. Herein, we developed a carbon black (CB)/high density polyethylene (HDPE)/poly(vinylidene fluoride) (PVDF) composite with outstanding PTC reproducibility, by incorporating 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm][NTf2]) into the composite. After multiple repeated temperature cycles, the PTC performance of as-prepared material keeps almost unchanged and the varition of resistance at room temperature is less than 7%. Our studies revealed that [OMIm][NTf2] contributes to the improvement of PTC reproducibility in two ways: (i) it acts as an efficient plasticizer for refining the co-continuous phase morphology of HDPE/PVDE blends; (ii) it inhibits the crystallization of PVDF through the dilution effect, leading to more overlaps of the volume shrinkage process of HDPE and PVDF melt which results in the decrease of interface gap between HDPE and PVDF. This study demonstrated that ionic liquids as the multifunctional agents have great potential for improving the reproducibility in the application of the binary polymer based PTC composites.

A Recycling-Focused Assessment of the Oxidative Thermomechanical Degradation of HDPE Melt Containing Pro-oxidant

This study shows the effect of a pro-oxidant (oxo-biodegradable) additive on the oxidative thermomechanical degradation of high-density polyethylene (HDPE). It also allows us to predict the behavior of the material when subjected to mechanical recycling or to biodegradation. When HDPE, one of the most consumed thermoplastics worldwide, is transformed into a product or when subjected to primary and/or secondary recycling it will undergo thermomechanical degradation. According to current standards HDPE is not biodegradable, therefore pro-oxidants are added to many HDPE products, which can compromise the product's life. Knowledge on the influence of pro-oxidants on HDPE in the melt is limited and the objective of this study is to assess the behavior of HDPE containing pro-oxidant manganese stearate (MnSt) in the oxidative thermomechanical degradation process. Thermomechanical degradation tests were conducted in a closed-chamber torque rheometer. FTIR and SEC results agreed with those of torque rheometry and showed that oxidative thermomechanical degradation of HDPE increases with increasing manganese stearate concentration. Degradation resulted in an increase in the number of oxygenated functional groups, mainly ketones, aldehydes and carboxylic acids, and reduction in the weight-average molar mass of HDPE. MnSt may have acted both as a lubricant and pro-oxidant during processing with predominance of one or the other effect at different stages along the oxidative thermomechanical degradation of HDPE.

Shear Banding of a Fluid Flow with a Nonmonotonic Dependence of the Flow Stress on the Strain Rate

The problem of an enforced fluid flow in a flat channel with the counter motion of one of the walls was considered. The fluid was characterized by a nonmonotonic flow curve consisting of three segments; a left segment (an ascending branch), a middle segment (a descending branch), and a right segment (an ascending branch). The rheological properties of the fluid were described by the modified Vmogradov-Pokrovsky model. The constants of the model were determined using the results of rheological tests of a high-density polyethylene melt performed with a laser Doppler viscometer. All exact analytical solutions of this problem were obtained in a parametric form for the one-dimensional case. The profiles of the velocity, effective viscosity, and velocity gradient along the channel height are constructed for different values of the parameters of the rheological model. Three solutions exist for the same given stress field in the range of shear rates corresponding to the middle branch of the flow curve. One of them is unstable and physically unrealizable, while the other two solutions are stable; however, the loading prehistory determines which of them is observed. The solution corresponding to the left branch is monotonic, while the solution corresponding to the right branch of the curve demonstrates the flow stratification into “bands” with different strain rates and different physical and mechanical properties. At the same time, the dependence of the effective viscosity on the strain rate, which is a monotonically decreasing function, allows its representation in the form of an exponential series. The same pressure-flow problem is solved in the two-dimensional formulation by the finite-element method using the semiweak Galerkin formulation and an approximation function for the viscosity. The comparison of the numerical results and the analytical solution shows that they are similar with a sufficient degree of accuracy. In both cases, as the counter pressure difference approaches zero, a limiting transition to the Couette flow is impossible.

Realizing self-reinforcement of polyethylene via high-speed shear processing

As one of the most representative polyolefins, polyethylene (PE) constitutes the largest consumption of thermoplastics in the world. Thus, the high-performance issue of PE, such as effective self-reinforcement, represents highly expected demand in both of academic and industrial areas. However, it induces a materials engineering challenge due to the difficulties in preparations of multiphase materials and technological complexities of processing. Here, we report a readily accessible self-reinforcement behavior of high-density polyethylene (HDPE) realized via using a commercially available technique, high-speed shear extrusion. A common grade of HDPE can be enhanced significantly for nearly 60%, depending on the rotation speed. The chromatography indicates that the molecular weight of HDPE is nearly constant after experiencing high-shearing effect. While a quasi-solid-like character is detected in the HDPE melt, which could be attributed to the increment of entanglement causing by severe mixing during extrusion. Subsequently, the enhanced entanglement enables the appearances of high orientation structure and specific crystalline morphology, which are responsible for the mechanical reinforcement observed. Our present study offers a promising avenue to access the manufacture of structural parts using polyolefin resins.

Large-scale formation of shish-kebab in water-assisted injection-moulded high-density polyethylene with a high-molecular weight

To promote flow-induced orientation and reserve the formation of the shish-kebab structure, a modified injection-moulding technology named water-assisted injection moulding (WAIM), was applied to provide twice the shear flow and a rapid cooling rate on high-molecular weight high-density polyethylene (HDPE) melt in a mould cavity. Large-scale distribution of highly oriented shish-kebab was successfully achieved in a WAIM sample with a high-molecular weight. More importantly, the high-orientation degree of lamellae (larger than 0.4) in the thickness direction for a high-molecular weight WAIM sample is >60%, which is much more than a conventional injection-moulded sample (15%). This work provides a new insight to achieve injection-moulded products with enhanced oriented structures.