Effect of waste wax and chain structure on the mechanical and physical properties of polyethylene

The influence of adding waste wax, produced as a by-product of the low density polyethylene manufacturing process, on the thermal and mechanical properties of three types of polyethylene (PE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE), with 10, 20, 30 and 40wt.% was investigated. Polymer–wax mixing was effective with no apparent leakage of the wax during sample preparation, which was evident from the agreement between the theoretical and experimental values of enthalpy for all types of PE.The wax dispersion in the matrix strongly depends on the percentage of wax added to the polymer and the molecular structure of the polymer. It was found that increasing the wax content enhances the phase separation. LDPE undergoes less phase separation due to its highly branched structure composed of a network of short and long chain branches. The wax has no pronounced plasticising effect on the polymer. This is clearly manifested in LDPE as no change in the melting temperature occurred. LLDPE and HDPE were slightly affected by a high concentration of wax (30% and 40%). This is due to the non-uniform distribution of short chain branching along the LLDPE and HDPE main chains, which can interact with the wax structure.NPRP 4 – 465 – 2 – 173 from Qatar National Research Fund (a member of Qatar Foundation). Open Access funding from King Saud University

Modification of polyethylene by RF plasma in different/mixture gases

Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery.Funding: This publication was made possible by an Award JSREP07-022-3-010 from the Qatar National Research Fund (a member of The Qatar Foundation).Scopu

Natural aging of shape stabilized phase change materials based on paraffin wax

Natural aging of shape-stabilized phase change materials containing linear low density polyethylene (LLDPE), paraffin wax and expanded graphite (EG) in Qatari climate has been studied. It was found that expanded graphite significantly improved the performance of prepared SSPCMs in multiple ways. Firstly, EG suppressed leakage of paraffin wax from the compact shape of SSPCMs. The addition of 15 wt% of EG to shape stabilized phase change materials (SSPCMs) containing 50 wt% of wax caused a decreasing in the leakage of wax by 50% over 210 days of natural aging. Secondly, ?expanded graphite enhanced the photochemical stability of the blends; this was confirmed by FTIR analysis, where carbonyl index decreased with EG content. 1 2017 Elsevier LtdThis work was allowed by NPRP grant No.: 4 - 465 - 2-173 from the Qatar National Research Fund (A Member of The Qatar Foundation). The statements made herein are solely the responsibility of the authorsScopu

Foamy phase change materials based on linear low-density polyethylene and paraffin wax blends

Foamy phase-change materials (FPCMs) based on linear low-density polyethylene (LLDPE) blended with 30 wt.% of paraffin wax (W) were successfully prepared for the first time. The advantage of these materials is their double functionality. First, they serve as standard thermal insulators, and second, the paraffin wax acts as a phase change component that absorbs thermal energy (the latent heat) during melting if the temperature increases above its melting point, which ensures better heat protection of buildings, for instance, against overheating. The density of the porous fabricated FPCM was 0.2898 g/cm(3) with pore content 69 vol.% and gel portion achieved 27.5 wt.%. The thermal conductivity of the LLDPE/W foam was 0.09 W/m.K, whereas the thermal conductivity of the neat LLDPE foam prepared under the same conditions was 0.06 W/m.K, which caused a higher porosity of approximately 92 vol.%. The FPCM absorbed or released approximately 22-23 J/g during melting or cooling, respectively, and the material was stable under thermal and mechanical cycling.Qatar Foundation, QF; Qatar National Research Fund, QNR

Foamed phase change materials based on recycled polyethylene/paraffin wax blends

Foamed phase-change materials (FPCMs) were prepared using recycled linear low-density polyethylene (LLDPE) blended with 30 wt.% of paraffin wax (PW) and foamed by 1,1 '-azobiscarbamide. The protection of pores' collapse during foaming process was insured through chemical cross-linking by organic peroxide prior foaming. This work represents one of very few attempts for a preparation of polymeric phase change foams without a use of micro-encapsulated phase change component leading to the enhancement of the real PCM component (PW) within a final product. The porous structure of fabricated foams was analyzed using micro-computed tomography, and direct observation, and reconstruction of the internal structure was investigated. The porosity of FPCMs was about 85-87 vol.% and resulting thermal conductivity 0.054-0.086 W/m center dot K. Differential Scanning Calorimetry was used to determine the specific enthalpies of melting (22.4-25.1 J/g) what is the latent heat of materials utilized during a heat absorption. A stability of samples during 10 heating/cooling cycles was demonstrated. The phase change changes were also investigated using the dynamic mechanical analysis from 0 degrees to 65 degrees C during the 10 cycles, and the mechanical stability of the system and phase-change transition were clearly confirmed, as proved by DSC. Leaching test revealed a long-term release of PW (around 7% of its original content) from samples which were long term stored at temperatures over PW melting point. This is the usual problem concerning polymer/wax blends. The most common, industrially feasible solution is a lamination of products, for instance by aluminum foils. Finally, the measurement of the heat flow simulating the real conditions shows that samples containing PW decrease the energy passing through the sample from 68.56 to 34.88 kJ center dot m(-2). In this respect, FPCMs provide very effective double functionality, firstly common thermal insulators, and second, as the heat absorbers acting through melting of the PW and absorbing the excessive thermal energy during melting. This improves the heat protection of buildings and reduces temperature fluctuations within indoor spaces.Qatar National Research Fund (A Member of the Qatar Foundation) [13S-0127-200177]; Ministry of Education, Youth and Sports of the Czech Republic-DKRVO [RP/CPS/2020/003

Polyisobutylene (PIB)-NHC Supported Catalysts for Cross-Coupling Reactions: A Green and Sustainable Protocol

N-Heterocyclic Carbenes (NHCs): Over the last two decades N-Heterocyclic carbenes (NHCs) have immensely attracted chemists in nearly all fields of chemistry. N-Heterocyclic carbenes are commonly encountered in coordination chemistry, they are extensively used as ligands for organometallic complexes. Perhaps the biggest hit of NHCs ligands was their use in Grubbs II catalyst for olefin metathesis chemistry. It is noteworthy that the success of NHCs ligands in catalysis is due to several factors favoring their high activity, selectivity and stability when compared to the phosphine counterparts in Grubbs I catalyst [1]. Supported Catalysts: Increased environmental and health awareness requires that designing new metal-catalysts should focus not only on increasing activity and selectivity but also on finding new strategies that help chemists recycle and separate the metal-catalyst from the reaction mixture. In general, homogenous catalysis is preferred over heterogeneous catalysis. This is due to the higher turnover number, better selectivity and usually lower operating temperatures required. On the other hand, heterogeneous catalysis has the advantage of the ease of separation of the catalyst from the final products and is generally less expensive. One important strategy is to use catalysts attached to a heterogeneous support and separate them from the products by simple filtration. Alternatively, homogeneous catalysts that can self-separate from the products by selective solvent extraction would be of great interest. The frequency of their reuse would be environmentally beneficial and to a higher extent this should overcome the lower activity of conventional heterogeneous catalysts. Metal catalysts that can self-separate from the reaction mixture are of great importance due to the reduced metal leaching into the product mixture. In addition, their reuse and recovery make this overall process much greener compared to the conventional homogeneous/heterogeneous catalysis systems. Ever since Herrmann et al. [2] reported the polystyrene supported NHC-palladium catalyst, studies have largely been focused on the use of polymeric supports for NHC-palladium catalysts. While polyethylene-glycol-supported catalyst can be extracted with a polar solvent, Bergbreiter et al. [3] and others have showed that polyisobutylene (PIB) is a useful support for ligands and their metal catalysts (Pd, Ru...) having preferable solubility towards solvents with low polarities such as hexanes, heptanes and decanes. In all of these biphasic systems for cross-coupling/olefin metathesis, the design is mainly focused on the recovery and the reuse of the supported catalysts. Biphasic catalysis having thermomorphic behavior have witnessed great developments due to their temperature-dependent miscibility [4]. While reactions in these biphasic mixtures can be conducted under homogeneous conditions at high-temperatures, the supported catalysts and the products/by-products can be efficiently separated by restoring the biphasic conditions at a low-temperature (Scheme 1). Herein we report the synthesis of new PIB-supported N-heterocyclic carbenes ligands having two different frameworks and their Pd-complexes, 1 and 2. The use, recovery and effectiveness of catalysts are detailed in both Heck and Suzuki cross-coupling reactions (Scheme 2). Metal leaching to the polar phase will be discussed too. Scheme 2: Heck cross-coupling and Suzuki cross-coupling using catalysts 1 and 2.qscienc

Enhancing the UV/heat stability of LLDPE irrigation pipes via different stabilizer formulations

Herein different stabilizer formulations of linear low-density polyethylene (LLDPE) against UV- and heat-initiated degradation are described. The project aims at outdoor applications, such as irrigation piping and profiles, in the Middle East desert regions, where long-term weathering stability due to high temperatures and solar radiation is important. Two UV/heat formulations, without and with carbon black (CB) as pigment, were incorporated into LLDPE by melt compounding. Neat LLDPE and the stabilized compounds were exposed to accelerated UV and heat aging. Morphological analysis through scanning electron microscopy of the UV-exposed neat LLDPE showed more severe surface cracking compared to the CB-containing LLDPE, while all stabilized compounds did not show any surface degradation. Crack formation was less visible for the thermally aged samples. A significant decrease in molecular weight (MW) was observed for the neat UV-exposed LLDPE, while both unpigmented stabilized compounds showed little change in MW. Mechanical properties, thermal analysis, and carbonyl index results supported the morphological results, which confirmed that CB alone was slightly more effective in protecting the LLDPE against UV initiated degradation, but performed worse against thermal initiated degradation. UV1 and UV2 compounds were efficient against both UV- and heat-initiated degradation, with UV1 performing better for unpigmented compounds, and UV2 for the pigmented ones.This publication was made possible by the NPRP award (NPRP 9-161-1-030) from the Qatar National Research Fund (a member of The Qatar Foundation). We are also grateful to BASF and Sabo for supplying the additives at no cost. We further express our gratitude to Dr. Robert Brüll from Fraunhofer LBF, Darmstadt, Germany for doing the GPC analyses on our samples. The statements made herein are solely the responsibility of the author(s).Scopu

Effect of chain structure on the properties of Glass fibre/polyethylene composites

Three types of polyethylenes (low density: LDPE, medium density: MDPE, and high density: HDPE) were used to investigate the effect of chain branching on the dispersion and adhesion in Glass fibre reinforced polymer composites. The interaction between the polyethylene matrix and the Glass fibres was investigated in terms of differences in mechanical behaviour, morphological characteristics, rheological and thermal properties between the three polymer composites systems. Addition of Glass fibres enhanced the mechanical properties for all systems. The degree of enhancement, however, depended on the branching and crystallinity of each polymer. The long chain branching (LCB) in LDPE resulted in higher increases both in the Elastic (Young’s) modulus in the solid state and in the Storage modulus in the melt. The higher crystallinity of HDPE was responsible for higher increase in tensile strength and less fibre pull-out upon addition of Glass fibres. Rheological results also confirm the same observation for LCB. The addition of Glass fibres also resulted in improved thermal stability of the various polyethylene samples

A comparative study of the treatment of ethylene plant spent caustic by neutralization and classical and advanced oxidation

The treatment of spent caustic produced from an ethylene plant was investigated. In the case of neutralization alone it was found that the maximum removal of sulfide was at pH values below 5.5. The higher percentage removal of sulfides (99% at pH=1.5) was accompanied with the highest COD removal (88%). For classical oxidation using H2O2 the maximum COD removal percentage reached 89% at pH=2.5 and at a hydrogen peroxide concentration of 19mM/L. For the advanced oxidation using Fenton's process it was found that the maximum COD removal of 96.5% was achieved at a hydrogen peroxide/ferrous sulfate ratio of (7:1).The authors wish to acknowledge Qatar University for the financial support through an internal student grant ( QUST-CENG-SPR-12/13-17 ) . Also the authors would like to thank Dr. Ahmed Al Khatat for the help provided in the chemical analysis. Moreover, the authors would like to thank Qatar Petrochemical Company (QAPCO) for the supply of samples

An Adhesion Improvement of Low-Density Polyethylene to Aluminum through Modification with Functionalized Polymers

An interfacial adhesion improvement between low-density polyethylene (LDPE) and aluminum (Al) foil is an important challenge in designing multilayered packaging (TetraPak packaging type) due to insufficient inherent adhesion between both untreated materials. Therefore, extra adhesive layers are often used. The hydrophobic character of LDPE is responsible for poor adhesion to Al and can result in delamination. This study deals with the comparative study of the bulk modification of LDPE with various commercially available adhesive promoters with different chemical compositions to increase LDPE’s adhesive characteristics and ensure good adhesion in LDPE/Al laminates. A copolymer of ethylene and methacrylic acid; a terpolymer of ethylene, maleic anhydride, and acrylic ester; or maleated polyethylene (PE) were used as adhesive promoters, and their effect on adhesion improvement of LDPE to Al was investigated. The best adhesion improvement was observed in LDPE-modified samples with maleated PE, while 0.1 wt.% additive content significantly increased peel resistance (from zero to 105 N/m). An additional increase in additive content (0.5 wt.%) in LDPE led to stronger adhesion forces than the cohesion forces in Al foil. Adding 0.5 wt.% of maleated PE into LDPE improved the LDPE/Al laminates’ adhesion and can be applied in multilayered lamination applications