Polyethylene Process Research Articles

Further discussion on the reaction behaviour of triallyl isocyanurate in the UV radiation cross-linking process of polyethylene: a theoretical study.

Further theoretical investigation on the reaction behaviour of triallyl isocyanurate (TAIC) in the UV radiation cross-linking process of polyethylene (PE) is accomplished by density functional theory for high voltage cable insulation materials. The reaction potential energy information of the 13 reaction channels at B3LYP/6–311 + G(d,p) level are identified. These have been explored that the TAIC take part in the reaction behaviour on ground state during UV radiation cross-linking process and TAIC intra-molecular isomerization reaction itself. In addition, the results show that the effect of multiplication and acceleration for the cross-linking reaction of trimethylopropane trimethacrylate (TMPTMA) would be better than that of TAIC. It has further clarified the reasons why UV radiation cross-linking reaction of PE had been initiated by benzophenone (Bp), and the TAIC or TMPTMA needed to take part. The results obtained in the present study could directly guide both the optimization of UV radiation cross-linking PE process and the development of the insulation material of high-voltage cable in real application.

The crystallization and rheological behaviors of the ultrahigh molecular weight polyethylene swollen by petrolatum

In this paper, petrolatum was utilized as a swelling agent to improve the processability of ultrahigh molecular weight polyethylene (UHMWPE), and the microstructure, crystallization behaviors and rheological behaviors of these swollen UHMWPE were investigated. Petrolatum exhibits strong swelling ability and remarkably improves the chain mobility and processability of UHMWPE. With the increase of petrolatum concentration, more and more petrolatum molecules penetrate into the entangled chain networks of UHMWPE, and the enhanced chain disentanglements accelerate the crystallization of UHMWPE, strengthen the deformation breakage resistance of UHMWPE and make the chain segments of UHMWPE relax more quickly.

Continuous pyrolysis of organosolv lignin and application of biochar on gasification of high density polyethylene

In the pyrolysis of lignin, lignin tends to agglomerate during the feeding stage, and the char produced can expand easily to form foam that prevents continuous operation. To solve this problem, a new bench-scale rotary kiln reactor with alumina balls was used for the pyrolysis of organosolv lignin. Also, a bench-scale fixed-bed reactor was used as a reference reactor to gain an insight on the pyrolysis phenomena from rotary kiln reactor. Compared to the fixed bed reactor, the rotary kiln reactor resulted in a higher yield of organic phase oil with high selectivity to monomeric phenolic compounds. Moreover, a larger amount of CO2 was obtained from the rotary kiln reactor, which strongly suggests that decarboxylation is main deoxygenation path. Furthermore, a char without agglomeration and foaming inside the reactor was generated from the rotary kiln reactor. The catalytic properties of the chars produced from both reactors with nickel impregnation were tested for the gasification of high-density polyethylene to produce H2. Among the four different catalysts (Ni/Rotary Kiln char, Ni/Fixed Bed char, Ni/Al2O3, Ni/Activated carbon) tested, the Ni/Fixed Bed char exhibited the highest yield of H2 (~two times higher H2 generation) from the gasification process of high-density polyethylene. X-ray photoelectron spectroscopy and scanning electron microscopy offers that the high dispersion/distribution of Ni occurred when the fixed bed char was used as a support. All experimental findings from this study significantly suggest that Ni supported on char could be an economically viable catalyst for producing H2 from gasification of high-density polyethylene.

Macromol. React. Eng. 4/2019

Front Cover: This article demonstrates a method to parameterize predictive models for hydrocarbon solubility in semicrystalline polyethylenes. The method reproduces solubility data at high loading, as well as in the dilute (Henry) regime. Such models are useful in predicting hydrocarbon absorption in polymer granules produced in the Gas Phase Polyethylene process, supporting kinetic modeling and purging processes. This is reported by Bruce J. Savatsky, Joseph A. Moebus, and Brian. R. Greenhalgh in article 1900003.

Effect of ultraviolet light on the degradation of Low-Density and High-Density Polyethylene characterized by the weight loss and FTIR

In this study, the research was made to understand the knowledge widely related to the degradation process of polyethylene polymer. The mode of treatment that involves in the degradation process of polyethylene is physical treatment while the method of degradation used is photo-degradation of UV light. By using the physical treatment of UV irradiation light, it helps by affecting the bonding that holds the polymer together to break and weakens the plastic. From the result obtained in FTIR and SEM analysis, in FTIR spectrum of LDPE shows higher transmittance compared to FTIR spectrum of HDPE both UV-treated for 30 days. This indicates the high transmittance have few bonds to absorb light in the LDPE sample, low transmittance in HDPE sample means has high population of bonds which have vibrational energies corresponding to the incident light. For SEM result, the polyethylene for LDPE plastic sheet shows the best results for degradation and managed to reduce the weight loss at 87.5% compared to HDPE plastic which at 21.6%.

On secondary recycling of ZrO2-reinforced HDPE filament prepared from domestic waste for possible 3-D printing of bearings

In this study, an innovative route for secondary recycling (with zirconium oxide (ZrO2) reinforcement) has been proposed based on melt processing of high-density polyethylene (HDPE) in low-temperature bearing applications. Initially, secondary recycled HDPE, acrylonitrile butadiene styrene, and nylon 6 thermoplastic composites were investigated for melt flow index (MFI) according to ASTM D1238 standard. Based on the acceptable MFI, secondary recycled HDPE matrix was selected for second-stage processing on twin screw extrusion (TSE). The final process involves reinforcement of ZrO2 into HDPE matrix by TSE in 60:40 ratio (by weight %) for preparation of feedstock filament (for possible 3-D printing of bearings). The results of the study suggest that for processing of HDPE, 40% ZrO2 composite matrix, 50 r min−1 screw speed, 190°C barrel temperature, and 15 kg applied load are the best setting of TSE (for maximizing the tensile strength of feedstock filament). The results are also supported by wear properties, thermal stability, and morphological analysis (based on scanning electron microscopy and electron-dispersive X-ray analysis).

Non-isothermal crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO3

The processability of ultrahigh molecular weight polyethylene (UHMWPE) improved by oligomer-modified calcium carbonate (CaCO3) was observed in our previous work. In order to understand the effect of oligomer-modified CaCO3 on the crystallization of UHMWPE, the non-isothermal crystallization behavior and crystallization kinetics of UHMWPE composites filled by oligomer-modified CaCO3 was studied by differential scanning calorimetry in this work. Jeziorny and Mo methods were used to describe the non-isothermal crystallization kinetics of UHMWPE composites.The effect of modified filler content and cooling rate on the crystallization temperature and crystallization rate was discussed. The heterogeneous nucleation of modified CaCO3 slightly increases the crystallization temperature of UHMWPE. The crystallization enthalpy of UHMWPE composites is significantly higher than that of UHMWPE. The crystallization rate of UHMWPE composites depends on the filler contents and cooling rate.

Utilization of supercritical CO2 as a processing aid for preparation of ultrahigh molecular weight polyethylene/functionalized activated nanocarbon fibers

This is the first investigation to report the processing and properties of ultrahigh molecular weight polyethylene (UHMWPE)/functionalized activated nanocarbon (FANC) gel solutions with the aid of supercritical carbon dioxide (scCO2). The ultradrawing and ultimate tensile properties of scCO2UHMWPE and scCO2UHMWPE/FANC fibers were found to improve considerably compared to those of UHMWPE and UHMWPE/FANC fibers prepared in the conventional way. The maximum achievable draw ratio obtained for the optimal scCO2UHMWPE/FANC fibers drawn at 95°C reached 445. The highest tensile tenacity (σf) of the fully drawn scCO2UHMWPE/FANC fiber reached an extraordinary high value of 104 g/d, which is about 3.2 and 1.1 times of that of the optimal UHMWPE and UHMWPE/FANC fully drawn fibers, respectively. The σf obtained for the optimally fully drawn scCO2UHMWPE/FANC fiber is about 25 times of those of steel fibers and is the highest tensile tenacity ever reported for single‐stage drawn polymeric fibers. Considerably lower dynamic transition temperatures and evaluated thinner crystal lamellae nucleated off of extended chains or FANC nucleants were found for as‐prepared scCO2UHMWPE and scCO2UHMWPE/FANC fibers compared with UHMWPE and UHMWPE/FANC fibers, respectively. Specific surface area, morphological, and Fourier transform infrared analyses of the activated nanocarbon (ANC), acid‐treated activated nanocarbon (ATANC) and FANC nanofillers and investigation of thermal, morphological, and orientation factor properties of the as‐prepared and drawn UHMWPE, UHMWPE/FANC, scCO2UHMWPE, and scCO2UHMWPE/FANC fibers were performed to understand the remarkable ultradrawing, dynamic transition, and ultimate tensile properties obtained for scCO2UHMWPE and scCO2UHMWPE/FANC fibers. POLYM. ENG. SCI., 59:1462–1471 2019. © 2019 Society of Plastics Engineers

Co-gasification of beech-wood and polyethylene in a fluidized-bed reactor

The co-gasification of beech-wood and polyethylene has been investigated in a lab-scale fluidised-bed reactor in the presence of four different types of bed materials (silica sand, olivine, Na-Y zeolite and ZSM-5 zeolite). ZSM-5 zeolite is very effective as a catalytic bed material in fluidized-bed reactor for wood-only gasification and co-gasification in terms of high hydrogen production and CGE. Na-Y zeolite is more effective compared with ZSM-5 zeolite in co-gasification of the beech-wood and polyethylene process. The catalytic activity in co-gasification of beech-wood and polyethylene can be ranked accordingly: Na-Y zeolite > ZSM-5 zeolite > olivine. In general, higher amounts of steam injected in the fluidized-bed reactor and more polyethylene would lead to higher hydrogen production in the co-gasification process.

Silk fibroin coating through EDC/NHS crosslink is an effective method to promote graft remodeling of a polyethylene terephthalate artificial ligament.

Anterior cruciate ligament reconstruction using polyethylene terephthalate artificial ligaments is one of the research hotspots in sports medicine but it is still challenging to achieve biological healing. The purpose of this study was to modify polyethylene terephthalate ligament with silk fibroin through ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N-hydroxysuccinimide (NHS) crosslink and to investigate the performance of graft remodeling in vitro and in vivo. After silk fibroin coating, changes in the surface properties of ligament were characterized by scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy and water contact angle measurements. The compatibility of polyethylene terephthalate ligament with silk fibroin coating was investigated in vitro. The results showed the silk fibroin coating significantly improved adhesion, proliferation and extracellular matrix secretion of fibroblast cells. Moreover, a rabbit anterior cruciate ligament reconstruction model was established to evaluate the effect of ligament with silk fibroin coating in vivo. The gross observation and histological results showed that the silk fibroin coating significantly inhibited inflammation response and promoted new tissue regeneration with fusiform cells infiltration in and around the graft. Furthermore, the expressions of collagen I protein and mRNA in the silk fibroin-coated polyethylene terephthalate group were much higher than those in the control group according to the immunohistochemical and real-time polymerase chain reaction results. Therefore, silk fibroin coating through EDC/NHS crosslink promotes the biocompatibility and remodeling process of polyethylene terephthalate artificial ligament in vitro and in vivo. It can be considered as a potential solution to the problem of poor remodeling of artificial ligaments after anterior cruciate ligament reconstruction in the clinical applications.

Heat and Recrystallization Processes in Polyethylene–Cyanuric Acid Mixtures after Plastic Deformation under High Pressure

LDPE and SMPE mixtures with cyanuric acid (40–90 wt %) underwent plastic deformation under 0.5–3.0 GPa and were analyzed with DSC. We found that cold crystallization proceeds during heating the deformed mixtures in LDPE and the enthalpy of melting decreases. Ultrafine crystallites are formed in the mixtures with SMPE, and the enthalpy of melting increases by 1.8 times.

Tensile properties of friction stir welding of thermoplastic pipes based on a novel designed mechanism

One of the main challenges in recent friction stir welding (FSW) investigations is the welding of pipelines. Limited numbers of researches have been investigated on FSW of metallic pipes while the FSW of polymeric pipes still remains challenging. In the present study, the FSW process of high-density polyethylene (HDPE) pipes is developed which is to the best of our knowledge for the first time to be reported. A stepwise fixture design is performed in order to achieve complete and high-quality welds. It was concluded that using a holder with an inner expandable support helps to enhance the welding condition of pipes. The yield strength of friction stir welded pipes as one of the mechanical properties is investigated using Taguchi approach. Rotational speed, transverse speed, and tool offset are selected as input parameters. Results of analysis of variance (ANOVA) indicated that rotational speed is the most effective parameter on yield strength followed by tool offset and transverse speed. Based on the results of the signal to noise ratio (S/N) analysis, the optimum levels of input variables that give the maximum yield strength were 2500 rpm of rotational speed, 110 mm/min of transverse speed, and 3.5 mm of tool offset.

Potential Production of Olefins in Pyrolysis of Algerian Gas Condensate Compounded with Ethane

The present work aims to investigate the possibility of substituting ethane, usually used as pyrolysis feedstock, by the Algerian gas condensate compounded with ethane. Several experiments have been setup using different percentage dilutions (5, 10, and 20%) of Algerian gas condensate and its fractions (light, medium and heavy) compounded with ethane. The impacts of temperature, steam flow and flows of material on the yield and composition of pyrolysis products have also been investigated. High yields of ethylene (19 to 36%) and propylene (9 to 20%) were obtained in the pyrogas. The present study demonstrates the potential of the Algerian gas condensate product which can be valorized and used to enhance the yields of ethylene and propylene used in the production process of polyethylene and polypropylene.

A novel intelligent model integrating PLSR with RBF-Kernel based Extreme Learning Machine: Application to modelling petrochemical process

Abstract With the petrochemical process data getting complicated, building accurate and robust process analysis models has becoming a hot research. In this study, a novel intelligent model integrating PLSR with RBF-Kernel based Extreme Learning Machine (PLSR-RBFKELM) is proposed for overcoming the difficulties found in the conventional extreme learning machine when dealing with collinearity. In the proposed model, radial basis function kernel is employed instead of activation functions in the ELM hidden layer to effectively deal with the high nonlinearity problem of modeling data, and partial least square regression is utilized to solve the collinearity problem. In order to verify the performance, the proposed PLSR-RBFKELM model is applied to modeling one real-world petrochemical process - high density polyethylene process in the steady state. Simulation results demonstrate that the proposed model can achieve good performance in terms of accuracy and stability for static process modeling.

Theoretical study on the grafting reaction of maleimide and its derivatives to polyethylene in the UV radiation cross-linking process

Theoretical investigation on the reactions of the maleimide and its derivatives in the UV radiation cross-linking of polyethylene is accomplished by density functional theory. The reaction potential energy surface information of 12 reaction channels is determined at the B3LYP/6-311+G(d,p) level. The highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps, ionization potentials, and electron affinities of the maleimide and its derivatives are obtained. The calculated results show that the maleimide and its derivatives can be grafted to polyethylene chain during the UV radiation process. In addition, the calculated results also show that the reaction energy barrier of 1,8-bismaleimidotriethylene glycol grafted to polyethylene is lower than that of N-phenylmaleimide, and 1,8-bismaleimidotriethylene glycol can be used as cross-linking agent. The bismaleimide grafted to polyethylene can also be used as space charge inhibitor. This survey for dual function additive is expected to provide reliable information for the development of UV radiation cross-linking polyethylene process and high-voltage insulation cables exceed 500 kV in real application.

Flow-induced density fluctuation assisted nucleation in polyethylene.

The nucleation processes of polyethylene under quiescent and shear flow conditions are comparatively studied with all-atom molecular dynamics simulations. Under both conditions, nucleation is demonstrated to be a two-step process, which, however, proceeds via different intermediate orders. Quiescent nucleation is assisted by local order structures, while flow-induced nucleation is promoted by density fluctuation, which is a coupling effect of conformational and orientational orderings. Flow drives the transformation from flexible chains to conformational ordered segments and circumvents the entropic penalty, which is the most peculiar and rate-limited step in polymer crystallization. This work suggests that the acceleration of the nucleation rate in orders of magnitude by flow is mainly attributed to the different kinetics pathway via conformational/orientational ordering-density fluctuation-nucleation.

Pyrolysis Process of Mixed Polypropylene (PP) and High-Density Polyethylene (HDPE) Waste with Natural Zeolite as Catalyst

The reactor of the experiment was made from stainless steel with the diameter of 25 cm and the height of 30 cm. The liquid petroleum gas was used as a fuel in the reactor. The reactor was connected by the thermocouple that controls temperature variations at 410, 420, 430, and 450ºC. Raw material contained plastic bottles and waste caps, while the natural zeolite as a catalyst was dried and cut in dimensions of 3x3 cm. A gas as the reacted product was condensed using the first condenser, then the liquid product was collected. Uncondensed gaswas condensed again in the second condenser, then the liquid product was collected again. The volume of gas was calculated based on the water volume coming out of the gallon. Thiswas repeated with varied ratios of plastics to natural zeolite (67:33; 75:25; 80:20; and 83:17 wt%). Pyrolysis was run for two hours and every 20 minutes the sample was weighed to gauge the change inmass of gas and liquid. After 120 minutes, the solid sample was examined to identify the mass of final solid. Based on the research, at the temperature of 440ºC, the highest liquid yield was 68.42%. On the other hand, with the ratio of raw material to zeolite at 83:17 wt%, the largest yield of liquid was 87.31%. The liquid product in various temperature and comparisons of percentage of raw material to catalyst was found to meet diesel specifications based on The Decree of Director General of Fuels and Gas Year 200,8 Number 14,496 K/14/DJM/2,008.

The High Density Polyethylene Composite with Recycled Radiation Cross-Linked Filler of rHDPEx.

This article discusses the possibilities of using radiation cross-linked high density polyethylene (HDPEx) acting as a filler in the original high density polyethylene (HDPE) matrix. The newly created composite is one of the possible answers to questions relating to the processing of radiation cross-linked thermoplastics. Radiation cross-linked networking is—nowadays, a commonly used technology that can significantly modify the properties of many types of thermoplastics. This paper describes the influence of the concentration of filler, in the form of grit or powder obtained by the grinding/milling of products/industrial waste from radiation cross-linked high density polyethylene (rHDPEx) on the mechanical and processing properties and the composite structure. It was determined that, by varying the concentration of the filler, it is possible to influence the mechanical behaviour of the composite. The mechanical properties of the new composite—measured at room temperature, are generally comparable or better than the same properties of the original thermoplastic. This creates very good assumptions for the effective and economically acceptable, processing of high density polyethylene (rHDPEx) waste. Its processability however, is limited; it can be processed by injection moulding up to 60 wt %.

Textile applications of commercial photochromic dyes: part 7. A statistical investigation of the influence of photochromic dyes on the mechanical properties of thermoplastic fibres

The influence of the concentration of a commercial photochromic dye, incorporated into as-spun and drawn fibres produced from polyethylene and polypropylene, on their mechanical properties was investigated. As-spun fibres were produced by incorporating a commercial photochromic dye at different concentrations at the extrusion stage of the production process of polypropylene, polyethylene and polyester. The fibres from polypropylene and polyethylene, which showed photochromism when exposed to UV light, were then drawn, and their mechanical properties evaluated and analysed using a factorial experimental design, applying appropriate statistical methods. No further investigation was carried out on the polyester as the dye appeared to degrade at the higher temperatures required for its extrusion, leading to a brown fibre, which was not photochromic. According to the analyses, the most significant parameter influencing the mechanical properties of the as-spun fibres was the polymer type; the effect of the dye concentration was dominated by the significance of the polymer type. The effects of the multi-stage hot-drawing process used to produce the fibres on the mechanical properties of the drawn polypropylene and polyethylene fibres were characterised and statistically modelled. It was found that the dyeing concentration had a negative effect on the tenacity and the modulus of the drawn polypropylene fibres but a positive effect on the tenacity and the modulus of the drawn polyethylene fibres. A dye concentration of 0.2% on mass of polymer had a positive effect on the elongation of the drawn polypropylene and polyethylene fibres, whereas the higher dye concentration of 0.4% had a negative effect on the elongation of both drawn fibres. A new forecasting data source was obtained to optimise the selection of the polymer and the dye concentration and to specify the direction of modification, either increasing or decreasing, the significant process parameters.

Theoretical Study on the Grafting Reaction of Maleimide to Polyethylene in the UV Radiation Cross-Linking Process.

Theoretical investigation of the reaction of graft maleimide to polyethylene in the UV radiation cross-linking process is accomplished at the B3LYP/6-311+G(d,p) level for high-voltage cable insulation materials. The reaction potential energy surface of the nine reaction channels is identified. The results show that the N,N′-ethylenedimaleimide can connect two 4-methylheptane molecules and act as the cross-linking agent. The calculated reaction potential barrier of forming 4-methylheptane radical by maleimide is higher than that of maleic anhydride. The study is expected to provide a basis for optimizing the UV radiation cross-linking polyethylene process and development more than 500 kV high-voltage cable insulation materials in practical applications.