Influence of branching characteristics on thermal and mechanical properties of Ziegler–Natta and metallocene hexene linear low‐density polyethylene blends with low‐density polyethylene

The effect of the branch content (BC) and composition distribution (CD) of linear low‐density polyethylene (LLDPE) on the thermal and mechanical properties of its blends with LDPE were studied. All blends and pure resins were conditioned in a Haake PolyDrive blender at 190°C and in the presence of adequate amounts of antioxidant. Two metallocene LLDPEs (m‐LLDPE) and one Ziegler–Natta (ZN) hexene LLDPE were melt blended with the same LDPE. The effect of the BC was investigated by blending two hexene m‐LLDPEs of similar weight‐average molecular weights and molecular weight distributions but different BCs with the same LDPE. The effect of the CD was studied by using a ZN and an m‐LLDPE with similar weight‐average molecular weights, BCs, and comonomer type. Low‐BC m‐LLDPE blends showed separate crystallization whereas cocrystallization was observed in the high‐BC m‐LLDPE‐rich blends. However, ZN‐LLDPE/LDPE blends showed separate crystallization together with a third population of cocrystals. The influence of the crystallization behavior was reflected in the mechanical properties. The BC influenced the modulus, ultimate tensile strength, and toughness. The addition of a small amount of LDPE to a low‐BC m‐LLDPE resulted in a major improvement in the toughness, whereas the results for the high‐BC pair followed the additivity rule. ZN‐LLDPE blends with LDPE blends were found to be more compatible and exhibited superior mechanical properties compared to m‐LLDPE counterparts with the same weight‐average molecular weight and BC. All mechanical properties of ZN‐LLDPE blends follow the linear rule of mixtures. However, the CD had a stronger influence on the mechanical properties in comparison to the BC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2488–2498, 2005     

Self‐reinforcement of high‐density polyethylene/low‐density polyethylene prepared by oscillating packing injection molding under low pressure

This article reports the toughness improvement of high‐density polyethylene (HDPE) by low‐density polyethylene (LDPE) in oscillating packing injection molding, whereas tensile strength and modulus are greatly enhanced by oscillating packing at the same time. Compared with self‐reinforced pure HDPE, the tensile strength of HDPE/LDPE (80/20 wt %) keeps at the same level, and toughness increases. Multilayer structure on the fracture surface of self‐reinforced HDPE/LDPE specimens can be observed by scanning electron microscope. The central layer of the fracture surface breaks in a ductile manner, whereas the break of shear layer is somewhat brittle. The strength and modulus increase is due to the high orientation of macromolecules along the flow direction, refined crystallization, and shish‐kebab crystals. Differential scanning calorimetry and wide‐angle X‐ray diffraction find cocrystallization occurs between HDPE and LDPE. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 799–804, 1999     

Blend of high‐density polyethylene and a linear low‐density polyethylene with compositional‐invariant mechanical properties

This article presents the tensile properties and morphological characteristics of binary blends of the high‐density polyethylene (HDPE) and a linear low‐density polyethylene (LLDPE). Two constituents were melt blended in a single‐screw extruder. Injection‐molded specimens were evaluated for their mechanical properties by employing a Universal tensile tester and the morphological characteristics evaluated by using a differential scanning calorimeter and X‐ray diffractometer. It is interesting to observe that the mechanical properties remained invariant in the 10–90% LLDPE content. More specifically, the yield and breaking stresses of these blends are around 80% of the corresponding values of HDPE. The yield elongation and elongation‐at‐break are around 65% to corresponding values of HDPE and the modulus is 50% away. Furthermore, the melting endotherms and the crystallization exotherms of these blends are singlet in nature. They cluster around the corresponding thermal traces of HDPE. This singlet characteristic in thermal traces entails cocrystallization between these two constituting components. The clustering of thermal traces of blends near HDPE meant HDPE‐type of crystallites were formed. Being nearly similar crystallites of blends to that of HDPE indicates nearness in mechanical properties are observed. The X‐ray diffraction data also corroborate these observations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2604–2608, 2002     

Crystallization behavior of glass bead‐filled low‐density polyethylene composites

The effects of the filler content and the filler size on the crystallization and melting behavior of glass bead‐filled low‐density polyethylene (LDPE) composites have been studied by means of a differential scanning calorimeter (DSC). It is found that the values of melting enthalpy (ΔH_c) and degree of crystallinity (x_c) of the composites increase nonlinearly with increasing the volume fraction of glass beads, ϕ_f, when ϕ_f is greater than 5%; the crystallization temperatures (T_c) and the melting temperatures (T_m) of the composites are slightly higher than those of the pure LDPE; the effects of glass bead size on x_c, T_c, and T_m are insignificant at lower filler content; but the x_c for the LDPE filled with smaller glass beads is obviously greater than that of the filled system with bigger ones at higher ϕ_f. It suggests that small particles are more beneficial to increase in crystallinity of the composites than big ones, especially at higher filler content. In addition, the influence of the filler surface pretreated with a silane coupling agent on the crystallization behavior are not too outstanding at lower inclusion concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 687–692, 1999     

Biodegradability and degrading microbes of low‐density polyethylene

This article is intended to establish a comprehensive interpretation of the noticeable differences in the dynamic mechanical behaviors of polypropylene/talc composites with and without modified interphases. The latter are discussed on the basis of different surface treatments applied to the reinforcement particles. To this end, a series of 75/25 (w/w) polypropylene/talc composites with and without interfacial modifications from the reinforcement side were evaluated by dynamic mechanical analysis. The proven capability of this technique analysis to follow the transitions and structural and morphological changes in organic polymers, which are largely influenced by the degree of compatibility between the components of heterogeneous materials based on polymers, was used in this study to check and discuss the kinds and efficiencies of different physisorption‐ and chemisorption‐based processes carried out on the surface of talc particles. We tackled this study by embracing the different relaxation phenomena taking place in the polymer matrix. To this end, five different temperature intervals were distinguished according to the relaxation phenomena taking place. Finally, a correlation between the parameters on the microscopic scale and others on the macroscopic scale appeared to emerge. Thus, the interfacial effects caused by the modified reinforcements could be determined by observations on either scale. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Assessment and characterization of antifungal and antialgal performances for biocide‐enhanced linear low‐density polyethylene

In this work, four biocides were used for the purpose of growth inhibition of fungi and algae in linear low‐density polyethylene (LLDPE) specimens. Benzimidazol‐2‐yl‐carbamicacid methyl ester [carbendazim (CB)], 5‐chloro‐2‐(2,4‐dichlorophenoxy)phenol [triclosan (TS)], and 3‐iodo‐2‐propynyl N‐butylcarbamate [iodopropynyl butylcarbamate (IPBC)] were used as antifungal agents, and 2‐methylthio‐4‐ethylamino‐6‐tert‐butylamino‐triazin‐1,3,5 [terbutryn (TT)] was used as an antialgal agent. Antifungal performance was evaluated by disk diffusion and dry weight techniques, and antialgal activities were carried out by disk diffusion and chlorophyll A methods. Aspergillus niger TISTR 3245 and Chlorella vulgaris TISTR 8580 were used as the testing fungus and alga, respectively. The experimental results suggested that the wettabilities of LLDPE specimens changed with the incorporation of CB, TS, IPBC, and TT biocides without significant changes in chemical structures and mechanical properties of the LLDPE. IPBC with the recommended content of 10,000 ppm was found to give the most satisfactory growth inhibition of A. niger. Antifungal performance evaluations were dependent on the testing methods used, whereas those for antialgal activity were not. The optimum concentration of TT agent for effective killing of C. vulgaris was 750 ppm; this loading could be reduced from 750 to 250 ppm by the addition of either TS or IPBC agent. TS and IPBC could be used as antialgal promoters in the LLDPE specimens. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Effects of ultrasonic oscillations on processing behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene/low‐density polyethylene blends

The influences of ultrasonic oscillations on rheological behavior and mechanical properties of metallocene‐catalyzed linear low‐density polyethylene (mLLDPE)/low‐density polyethylene (LDPE) blends were investigated. The experimental results showed that the presence of ultrasonic oscillations can increase the extrusion productivity of mLLDPE/LDPE blends and decrease their die pressure and melt viscosity during extrusion. Incorporation of LDPE increases the critical shear rate for sharkskin formation of extrudate, crystallinity, and mechanical properties of mLLDPE. The processing behavior and mechanical properties of mLLDPE/LDPE blends were further improved in the presence of ultrasonic oscillations during extrusion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2522–2527, 2004     

Novel heterocyclic synthesis and investigation on radiation‐grafted low‐density polyethylene with 2‐N‐vinylpyrrolidone

Radiation‐induced graft polymerization of low‐density polyethylene with N‐vinylpyrrolidone, LDPE‐g‐PNVP, was used as a starting material for the synthesis of polyfunctionally substituted heterocyclic products. Thus, LDPE‐g‐PNVP reacts with ylidenemalononitrile derivatives to give the Michael addition products. In multistep reaction, LDPE‐g‐PNVP reacts with N,N‐dimethylformamide dimethyl acetal (DMFDMA), hydrazine hydrate and malononitrile, respectively, to give a hydropyrrolopyridazine derivative. The latter could also be prepared via the reaction of LDPE‐g‐PNVP with DMFDMA, followed by treating with cyanoacetohydrazide. Also, LDPE‐g‐PNVP reacts with malononitrile to give an adduct product, dimer malononitrile derivative 13. The latter reacts with sulfur element to afford the thiophene derivative. Furthermore, this adduct reacts with hydrazine hydrate to isolate the original starting material, LDPE‐g‐PNVP, and aminopyridine derivative. The resulted films were characterized by infrared (IR) spectroscopy, ¹H nuclear magnetic resonance (¹H‐NMR) mass spectroscopy, elemental analysis, swelling behavior, and electron scanning microscope. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2963–2970, 1999     

Mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene/wax blends

The mechanical properties of uncrosslinked and crosslinked linear low‐density polyethylene (LLDPE)/wax blends were investigated, using differential scanning calorimetry (DSC), tensile testing, and melt flow indexing. A decrease in the degree of crystallinity, as determined from the DSC melting enthalpies, was observed with an increase in the dicumyl peroxide (DCP) concentration. The Young's modulus increased with increased wax portions, and there was a higher increase for crosslinked blends. The yield stress generally decreased with increased peroxide content. Crosslinking caused an increase in elongation at yield, but increased wax content caused a decrease in elongation at yield. The stress at break generally increased with increasing peroxide content, but it decreased with increased wax content. The elongation at break decreased with an increase in the DCP concentration. Melt flow rate measurements indicated a mutual miscibility in LLDPE/wax blends. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 973–980, 2001     

Degradation of polyethylene during extrusion. II. Degradation of low‐density polyethylene,linear low‐density polyethylene,and high‐density polyethylene in film extrusion

The degradation of different polyethylenes—low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and high‐density polyethylene (HDPE)—with and without antioxidants and at different oxygen concentrations in the polymer granulates, have been studied in extrusion coating processing. The degradation was followed by online rheometry, size exclusion chromatography, surface oxidation index measurements, and gas chromatography–mass spectrometry. The degradations start in the extruder where primary radicals are formed, which are subject to the auto‐oxidation when oxygen is present. In the extruder, crosslinking or chain scissions reactions are dominating at low and high melt temperatures, respectively, for LDPE, and chain scission is overall dominating for the more linear LLDPE and HDPE resins. Additives such as antioxidants react with primary radicals formed in the melt. Degradation taking place in the film between the die orifice, and the quenching point is mainly related to the exposure time to air oxygen. Melt temperatures above 280°C give a dominating surface oxidation, which increases with the exposure time to air between die orifice and quenching too. A number of degradation products were identified—for example, aldehydes and organic acids—which were present in homologous series. The total amount of aldehydes and acids for each number of chain carbon atoms were appeared in the order of C5>C4>C6>C7?C2 for LDPE, C5>C6>C4>C7?C2 for LLDPE, and C5>C6>C7>C4?C2 for HDPE. The total amounts of oxidized compounds presented in the films were related to the processing conditions. Polymer melts exposed to oxygen at the highest temperatures and longest times showed the presence dialdehydes, in addition to the aldehydes and acids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1525–1537, 2004     

Molecular characteristics of room‐temperature soluble fractions of low‐density polyethylene film resins

The molecular characteristics of the room‐temperature soluble fractions (RT solubles) of three low‐density polyethylene film resins were characterized by size‐exclusion chromatography (SEC), SEC combined with FTIR (SEC–FTIR), and nuclear magnetic resonance spectroscopy (NMR). The high‐molecular‐weight components of the RT solubles were found to be highly branched components with uniform short‐chain branching (SCB) profiles. For the low‐molecular‐weight components, however, SCB content was a function of molecular weight (MW), increasing with an increase in MW. When the chain ends were considered as SCB equivalents, the distribution of the sum of SCB and chain ends across the molecular weight distribution was practically flat, suggesting that the driving force for polymer chains remaining in solution at RT was the length of the undisrupted methylene sequence in the backbone, or methylene run length, which was too short to form crystal lamellae with a melting temperature above RT, regardless of the molecular weight of the polymer. Moreover, the NMR results revealed that the polymer components of the RT solubles had “superrandom” SCB distributions, that is, the fraction of comonomer clusters in the polymer chains of the RT solubles was lower than that predicted by Bernoullian statistical analysis, indicating that the probability of adding a comonomer to a comonomer‐ended propagating chain was lower than that of adding a comonomer to an ethylene‐ended one, presumably because of an unfavorable steric effect. Furthermore, contrary to the common belief that RT solubles are mainly low‐molecular‐weight polymers, high‐molecular‐weight components were found in high concentrations in the RT solubles, with a cutoff MW as high as 1,000,000 g/mol. The proportion of RT solubles in the film resins was found to depend on the type of resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4992–5006, 2006     

Flame synthesis of mixed tin‐silver‐copper nanopowders and conductive coatings

The single‐step direct synthesis of tin‐silver‐copper nanopowders and nanostructured coatings using the flame‐based high‐temperature reducing jet (HTRJ) process is reported. Nanostructured coatings were deposited and sintered within the HTRJ reactor to study the effect of reductive sintering temperature on their electrical conductivity and surface morphology. Although the ultimate application of these nanoparticles is in printed electronics, which requires dispersing them as stable inks before depositing and sintering them, our approach of direct deposition from the gas phase provides an upper limit on the conductivity achievable with a given composition. The directly deposited coatings had high electrical conductivity, including a value of 2 × 10⁶ S/m for 36 wt % Cu‐40 wt % Ag‐24 wt % Sn sintered at 200°C. This is twice the conductivity of a pure silver coating prepared under similar conditions. Moreover, similarly high electrical conductivity was achieved using only 20% Ag with sintering at 300°C. © 2015 American Institute of Chemical Engineers AIChE J, 62: 408–414, 2016     

Heat‐shrinkable polymer blends based on grafted low‐density polyethylene and polyurethane elastomer. Part I

Blends prepared by melt‐mixing of thermoplastic material‐elastomer have gained considerable attention in recent years. Heat‐shrinkability of polymer, which is dependent on elastic memory, can be introduced into the system in the form of an elastomeric phase. The present study deals with the measurement of the heat‐shrinkability of the blend of grafted polyethylene and polyurethane elastomer. Interchain crosslinking between grafted polyethylene and elastomer improves shrinkability. High‐temperature performance of the sample depends on the degree of interchain crosslinking. Probable interactions between the rubber and plastic phase are confirmed by IR spectroscopy. Extraction of the elastomeric phase is restricted due to interchain crosslinking as confirmed by SEM study. © 2000 Society of Chemical Industry     

Multiple shape memory effects of trans‐1,4‐polyisoprene and low‐density polyethylene blends

A novel series of shape memory blends of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) were prepared using a simple physical blending method. The mechanical, thermal and shape memory properties of the blends were studied and schemes proposed to explain their dual and triple shape memory behaviors. It was found that the microstructures played an important role in the shape memory process. In TPI/LDPE blends, both the TPI crosslinking network and LDPE crystalline regions could work as fixed domains, while crystalline regions of LDPE or TPI could act as reversible domains. The shape memory behaviors were determined by the components of the fixed and reversible domains. When the blend ratio of TPI/LDPE was 50/50, the blends showed excellent dual and triple shape memory properties with both high shape fixity ratio and shape recovery ratio. © 2017 Society of Chemical Industry     

Compatibilizer in waste tire powder and low‐density polyethylene blends and the blends modified asphalt

With the increasing ratio of waste tire powder (WTP) to low‐density polyethylene (LDPE), the hardness and tensile strength of the WTP/LDPE blends decreased while the elongation at break increased. Five kinds of compatibilizers, such as maleic anhydride‐grafted polyethylene (PE‐g‐MA), maleic anhydride‐grafted ethylene‐octene copolymer (POE‐g‐MA), maleic anhydride‐grafted linear LDPE, maleic anhydride‐grafted ethylene vinyl‐acetate copolymer, and maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene, were incorporated to prepare WTP/LDPE blends, respectively. PE‐g‐MA and POE‐g‐MA reinforced the tensile stress and toughness of the blends. The toughness value of POE‐g‐MA incorporating blends was the highest, reached to 2032.3 MJ/m³, while that of the control was only 1402.9 MJ/m³. Therefore, POE‐g‐MA was selected as asphalt modifier. The toughness value reached to the highest level when the content of POE‐g‐MA was about 8%. Besides that the softening point of the modified asphalt would be higher than 60°C, whereas the content of WTP/LDPE blend was more than 5%, and the blends were mixed by stirring under the shearing speed of 3000 rpm for 20 min. Especially, when the blend content was 8.5%, the softening point arrived at 82°C, contributing to asphalt strength and elastic properties in a wide range of temperature. In addition, the swelling property of POE‐g‐MA/WTP/LDPE blend was better than that of the other compalibitizers, which indicated that POE‐g‐MA /WTP/LDPE blend was much compatible with asphalt. Also, the excellent compatibility would result in the good mechanical and processing properties of the modified asphalt. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dielectric relaxation of polar aromatics in unoriented and oriented linear low‐density polyethylene

The dielectric behavior of some polar aromatics dissolved in nonpolar unoriented and stretched linear low‐density polyethylene was investigated within the temperature region between 150 and 350 K. The measurements were carried out in the frequency range 1 kHz to 10 MHz. The maximum temperatures and the half widths of the loss tangent peaks depend upon the shape and the polar structure of guest molecules. Stretching the samples induced a shift of the loss tangent to higher temperatures, decreased the height, and increased the width of tan δ peak. The activation energy is also influenced by the type of guest molecules and orientation of polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1278–1282, 2001     

Oxidation and crosslinking processes during thermal aging of low‐density polyethylene films

This work analyzes the influence of thermal degradation on the microstructure and the mechanical properties of low‐density polyethylene subjected to aging at 70°C in the dark for times up to 21 months. It is found that the polymer shows a gradual increase of its elastic modulus and a dramatic reduction of its ductility, due to secondary crystallization. Infrared spectroscopy (FTIR) reveals the autoaccelerated oxidation of the polymer after 5 months aging. It is observed that the unsaturated vinylidene groups initially present in the material are gradually overridden by vinyl groups and, eventually, by t‐vinylene groups. Nuclear magnetic resonance (¹³C NMR) shows that the initial butyl chain branches are progressively completed by shorter ramifications, namely ethyl branches. These results are discussed in term of macromolecular mechanisms: (i) oxidation, (ii) chain scission, and (iii) crosslinking. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Melt processable conducting poly(aniline‐co‐o‐anisidine)/linear low‐density polyethylene composites with ethylene‐acrylic acid copolymer as compatibilizer

Conducting composites of aniline/o‐anisidine copolymer doped by dodecylbenzenesulfonic acid (P(An‐co‐oAs)‐DBSA), linear low‐density polyethylene (LLDPE), and ethylene–acrylic acid copolymer (EAA) as compatibilizer were prepared by melt processing. The effects of composition on electrical conductivity, resistivity‐temperature characteristic, and mechanical properties were also investigated. The electrical conductivity of ternary composites markedly increased due to compatibilizition and protonation effect of the EAA. The SEM micrograph shows that the compatibility between the P(An‐co‐oAs)‐DBSA and the LLDPE matrix is enhanced after the introduction of EAA. The positive temperature coefficient of resistivity characteristic is observed. Tensile strength of P(An‐co‐oAs)‐DBSA/LLDPE/EAA composites is improved, compared with P(An‐co‐oAs)‐DBSA/LLDPE composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1511–1516, 2005     

Rice bran‐filled biodegradable low‐density polyethylene films: Development and characterization for packaging applications

Rice bran was incorporated into low‐density polyethylene (LDPE) at different concentrations by compounding in a twin‐screw extruder and blown into films of uniform thickness. The rice bran incorporation influenced physical, mechanical, barrier, optical, thermal properties, and biodegradation of LDPE. The mechanical and optical properties decreased as the percentage of rice bran increased. The effect of rice bran on the morphology of LDPE blends was examined using scanning electron microscopy. Oxygen transmission rate and water vapor transmission rate increased with the increased content of rice bran. Addition of rice bran did not alter the melting temperature (T_m) of the blends; however the thermal stability decreased, while glass transition temperature (T_g) increased. Kinetics of thermal degradation was also investigated and the activation energy for thermal degradation indicated that for up to 10% filler addition, the dispersion and interfacial adhesion of rice bran particles in LDPE was good. Aerobic biodegradation tests using municipal sewage sludge and biodegradation studies using specific microorganism (Streptomyces species) revealed that the films are biodegradable. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4514–4522, 2006     

Essential work of fracture evaluation of fracture behavior of glass bead filled linear low‐density polyethylene

The effect of the glass bead (GB) size and bead content on the fracture behavior of GB‐filled linear low‐density polyethylene (LLDPE) composites was evaluated by means of the essential work of fracture (EWF). The results indicated the specific EWF (w_e) is lower for the composites than that of pure LLDPE and the obtained w_e values do not show significant differences for the filled samples with different GB diameters. The non‐EWF or plastic work (βw_p) also decreased with the addition of GBs, indicating that less energy is absorbed during the fracture process for the composites filled with different diameter GBs. For the composites filled with GBs of different contents, the w_e decreased with increasing GB contents and the βw_p that was higher than that of pure LLDPE at relatively low contents also decreased with the content of GBs. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1781–1787, 2006