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Abstract In this paper, two Zigler-Natta catalysts (ZNCs) were used to synthesize a commercially available linear low-density polyethylene (LLDPE), widely used in the packaging industry, on an industrial scale. The [...]

This article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high-density polyethylene (HDPE). HDPE resins were synthesized using several titanium-magnesium-supported Ziegler-Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80[degrees]C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements ([M.sub.e]) and the average lamella thickness based on the Gibbs-Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80[degrees]C to the crystallizable fraction in the range of 80-90[degrees]C. KEYWORDS gel permeation chromatography (GPC), mechanical properties, molecular weight distribution, polyethylene (PE), structure-property relations, 1 | INTRODUCTION High-density polyethylene (HDPE) is a common thermoplastic polymer, especially in packaging, houseware, kitchenware, plastic containers, and crates. [1] The production process, catalyst, and reaction are the main [...]

The relationship between career resin of carbon black (CB) masterbatch and the performance of bimodal polyethylene pipes (PE100) under ultraviolet (UV) irradiation and the long-term stability of black PE100 with different comonomer content have been investigated. For this purpose, two different CB masterbatches varying in carrier resin were selected and added to two PE100 pipes. Samples were exposed to UV irradiation, and then thermal, mechanical, and rheological properties were explored using differential scanning coloriemetry (DSC), tensile, and rheometry analyses. Additionally, Fourier transformed-infrared spectroscopy (FTIR) has been performed to characterize the structural changes of PE100 samples under UV irradiation. According to rheological results, the PE100 sample containing more comonomer underwent a higher degree of degradation. Thermal and mechanical results reveal that the masterbatch composed of highdensity polyethylene (HDPE) as carrier resin has a better influence on PE pipes' UV stability with less comonomer content. KEYWORDS carbon black, HDPE, photodegradation, pipe, rheology, UV irradiation, UV stability, 1 | INTRODUCTION Easy to install, light, flexible, and corrosion-free are the features that have made polyethylene (PE) pipes a material of choice for the network of gas and water [...]

This study integrates advanced mathematical modeling and experimental methodologies to investigate the simultaneous impact of modifications in the split ratio and molecular weight (MW) of chains on the rheological and mechanical properties of bimodal polyethylene (BiPE) resins. The outcomes underscored the viability of fine‐tuning the molecular weight distribution (MWD) of a BiPE resin by augmenting the MW of high molecular weight (HMW) chains while simultaneously diminishing their proportion in the final alloy formulation. In addition, the experimental results illuminated the prospect of attaining a targeted melt flow index for the final polymers by elevating the MW of HMW chains alongside an increase in the proportion of low molecular weight chains. Significantly, these adjustments resulted in remarkable enhancements in the shear thinning index and strain hardening modulus of the fabricated resins. [ABSTRACT FROM AUTHOR]

The present study encompasses the utilization of a mixture of 1-butene and 1-hexene comonomers for the large-scale production of a film-grade linear low-density polyethylene (LLDPE) resin. The goal involves assessing the impact stemming from the partial replacement of 1-butene with 1-hexene on the thermal, physical, mechanical and rheological properties of the resultant resin, juxtaposed against an LLDPE counterpart exclusively produced by 1-butene as the comonomer. Although the comprehensive examination of key physical, thermal, rheological and mechanical characteristics indicates nominal influence due to the substitution, a marked escalation materializes in both the tear resistance and slow crack growth (SCG) resilience of the LLDPE resins formulated through the amalgamation of these comonomers. Specifically, the tear and SCG resistance of the proposed resin exhibit an extraordinary surge exceeding 60% and 30%, respectively. This discernible enhancement underscores the viability of the proposed technique as a propitious avenue for augmenting the requisite mechanical properties, obviating the need for an all-encompassing shift from 1-butene to longer-chain α-olefin comonomers. [ABSTRACT FROM AUTHOR]

This paper presents applications of a new class of fibre optic acoustic emission (FOAE) sensor to monitor the operation of fluidized bed reactors used in polyethylene production. Specifically, the sensor was implemented to detect undesired, abnormal phenomena related to particle agglomeration, wall sheeting, fine overflow, and variations in the superficial gas velocity. The experiments were executed using a fluidized bed cold model setup for polyethylene powders with average particle sizes of 250, 1000, and 2000 μm. The results demonstrated that the presence of agglomerated particles in the fluidized bed reactor increases the kurtosis of the acoustic emission (AE) signal. Furthermore, the overflow of small particles can be detected by mounting the FOAE sensor below the gas distributor plate and monitoring an increase in the root mean square (RMS) of the AE signal. The AE signal RMS increased with the rising superficial gas velocity. Besides, forming a sheet layer on the reactor wall decreased the AE signal RMS. The proposed sensor's main benefits are its simple design, rapid response to abnormal conditions in the fluidized bed reactor, immunity against electromagnetic noise, high‐temperature resistance, and safety in hazardous areas. [ABSTRACT FROM AUTHOR]

In this study, the relationship between the characteristics of catalysts and polymerization conditions with catalyst behavior and polymer properties in the ethylene/α-olefin (co)polymerization using Ziegler–Natta catalyst (TiCl4/MgCl2 based) is investigated. The results showed that the differences in the characteristics of a catalyst such as particle size,surface area, porosity and particle size distribution of catalyst, and different polymerization conditions such as the presence of comonomer, can be a very important factors in determining catalyst behavior and product properties. For this purpose, two catalysts (cat1, cat2) TiCl4/MgCl2 based have been used and ethylene/α-olefin(co)polymerization was performed in slurry phase. Comparison results of DSC copolymers produced using both cat1 and cat2 showed that copolymerization in the presence of comonomers using cat2 catalyst shows better activity and comonomer incorporation than cat1 due to higher titanium content in the surface, larger surface area, possibility of access to more active centers. Besides that results of RMS showed that the presence of comonomer 1-butene and 1-hexane in the copolymers due to the increase in melt flow index, molecular weight has decreased and as a result, the storage and loss modulus has decreased. The inverse method with Van Ruymbeke model showed that the presence of 1-butaene comonomer in copolymerization with cat1 caused a change in the distribution of active catalytic centers and narrowed the molecular weight distribution. [ABSTRACT FROM AUTHOR]

In this paper, using a comprehensive study, we have investigated the effect of various polymerization parameters during the synthesis of bimodal polyethylene resins on their rheological and mechanical properties. Bimodal polyethylene resins were synthesized in two subsequent stages in a lab‐scale reactor by manipulating a set of parameters such as C2/H2 ratios in the first and second stages, the split value, and the comonomer type. The results showed that the comonomer type and C2/H2 ratio of the second stage of the polymerization are the most critical parameters that control the final resins' slow crack growth resistance properties. On the other hand, the shear‐thinning behavior of the resins is mainly controlled by the first‐stage polymers. Although the C2/H2 ratio of the first stage results in a moderate effect on the rheological properties of the final resins, its split value governs the flow characteristics of the final molten polymers under high shear rates. [ABSTRACT FROM AUTHOR]

In this study, commercially available, milled, and heat-treated Mg(OEt)2 were used as the precursors in the synthesis procedure of industrially-favorable supported Ziegler–Natta catalysts. The effects of milling and heat-treatment of the support were completely investigated during the catalyst synthesis and polymerization using SEM, PSD, BET, DCS, and XRD techniques. It was found that despite the support treatments had no significant effect on the elemental analysis results of the catalysts, the morphology of the catalyst pores was very sensitive to support manipulation, and bottleneck-type pores were predominated in the catalysts which were made using the non-manipulated supports. On the other hand, the catalysts which were made using the milled and not-milled supports showed a clear difference between the activity, particle size, and particle size distribution of the catalysts. Also, a high level of stacking disorder and high grain size was observed in the crystal structure of the catalyst made using the commercially available support. In the following, competition between fragmentation and replication was investigated in the synthesized samples, and an attempt was made to link the stacking disorder (in the catalyst structure) to the ease of the fragmentation process. Finally, using practical observation, a mechanism was proposed to justify the changes in the morphology of the catalysts during synthesis procedures. We claimed that milling and especially heat-treating of the support leads to the ordering of the MgCl2 stacking structure. [ABSTRACT FROM AUTHOR]

Although Ziegler-Natta catalysts were discovered more than four decades ago, many aspects of their characteristics are not fully understood. The effect of the support particle size on the final properties and performance of these catalysts is one of them. In this article, we present the effect of milling and heat-treating the Mg(OEt)2 support on the properties of the final catalysts and subsequently the resulting co-polymer powders. It was found that while the support milling has no significant effect on the elemental analysis results of the catalysts, the catalysts made by the milled and not-milled supports show a clear difference between the activity, particle size, and particle size distribution of the catalysts. On the other hand, the morphology of the catalyst pores is very sensitive to support manipulation, and bottleneck-type pores are predominant in the catalysts made by the nonmanipulated supports. Finally, it was found that the incorporation and the distribution of co-monomers in the final polymer chains depend on the manipulation of the raw support, and the use of milled and heat-treated supports results in the formation of co-monomer-sensitive catalysts. [ABSTRACT FROM AUTHOR]

Many researchers have studied the effects of donors, promoters and alkyl aluminum compounds on the polymerization catalysts, the polymerization process and the final properties of polymers. Nevertheless, changing the operating parameters (such as temperature, duration and order of steps) during the catalyst synthesis process is an industrially popular solution to the challenge of modifying Ziegler-Natta catalysts (without adding, removing, or changing raw materials). In the present study, the effects of important heat treatment parameters such as titanation temperature, tempering time and tempering temperature, are systematically considered during the synthesis of a titanium-magnesium-based Ziegler-Natta catalyst. The results show that using harsher conditions during the titanation or tempering phase leads to less active catalysts that can be used to produce higher molecular weight polyethylene chains. Moreover, the tempering time was determined as the most important parameter for controlling the activity of the catalysts and the molecular weight of the final polymers. Finally, it was found that setting the tempering time at a certain level, regardless of the magnitude of the other parameters, leads to the production of catalysts at a unique level of activity. [ABSTRACT FROM AUTHOR]