Thermal, mechanical and electrical properties of copper powder filled low-density and linear low-density polyethylene composites

Low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE) with different copper contents were prepared by melt mixing. The copper powder particle distributions were found to be relatively uniform at both low and high copper contents. There was cluster formation of copper particles at higher Cu contents, as well as the formation of percolation paths of copper in the PE matrices. The DSC results show that Cu content has little influence on the melting temperatures of LDPE and LLDPE in these composites. From melting enthalpy results it seems as if copper particles act as nucleating agents, giving rise to increased crystallinities of the polyethylene. The thermal stability of the LDPE filled with Cu powder is better than that for the unfilled polymer. The LLDPE composites show better stability only at lower Cu contents. Generally, the composites show poorer mechanical properties (except Young's modulus) compared to the unfilled polymers. The thermal and electrical conductivities of the composites were higher than that of the pure polyethylene matrix for both the LDPE and LLDPE. From these results the percolation concentration was determined as 18.7 vol.% copper for both polymers.     

Solid-state relaxations in linear low-density (1-octene comonomer), low-density,and high-density polyethylene blends

Extensive thermal and relaxational behavior in the blends of linear low-density polyethylene (LLDPE) (1-octene comonomer) with low-density polyethylene (LDPE) and high-density polyethylene (HDPE) have been investigated to elucidate miscibility and molecular relaxations in the crystalline and amorphous phases by using a differential scanning calorimeter (DSC) and a dynamic mechanical thermal analyzer (DMTA). In the LLDPE/LDPE blends, two distinct endotherms during melting and crystallization by DSC were observed supporting the belief that LLDPE and LDPE exclude one another during crystallization. However, the dynamic mechanical β and γ relaxations of the blends indicate that the two constituents are miscible in the amorphous phase, while LLDPE dominates α relaxation. In the LLDPE/HDPE system, there was a single composition-dependent peak during melting and crystallization, and the heat of fusion varied linearly with composition supporting the incorporation of HDPE into the LLDPE crystals. The dynamic mechanical α, β, and γ relaxations of the blends display an intermediate behavior that indicates miscibility in both the crystalline and amorphous phases. In the LDPE/HDPE blend, the melting or crystallization peaks of LDPE were strongly influenced by HDPE. The behavior of the α relaxation was dominated by HDPE, while those of β and γ relaxations were intermediate of the constituents, which were similar to those of the LLDPE/HDPE blends. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1633–1642, 1997     

Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

Structure and properties of compatibilized recycled poly(ethylene terephthalate)/linear low density polyethylene blends

Blends of recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) were compatibilized with poly(styrene-ethylene/butyldiene-styrene) (SEBS) and maleic anhydride-grafted poly(styrene-ethylene/butyldiene-styrene) (SEBS-g-MA). Effects of compatilizer were evaluated systematically by study of mechanical, thermal and morphology properties together with crystallization behavior of PET. Tensile properties of the blends were improved effectively by the addition of 10 wt% SEBS-g-MA, elongation at break and charpy impact strength were increased with the increasing content of compatilizer. SEBS-g-MA is more effectual on mechanical properties of R-PET/LLDPE blends than SEBS. DSC analysis illustrates crystallinities of PET and LLDPE were increased by compatilizer at annealing condition. WAXD and FT-IR spectra show that annealing influences crystallization behavior of PET. Different compatilizer content results in different morphology structure, in particular, higher SEBS-g-MA content can induce the formation of a salami microstructure.     

Thermorheological properties of LLDPE/LDPE blends: Effects of production technology of LLDPE

The thermorheological behavior of a number of LLDPE/LDPE blends was studied with emphasis on the effects of the production technology of the linear low‐density polyethylene (LLDPE) and the effects of long chain branching (LCB). Two Ziegler‐Natta LLDPE's (LL3001.32 and Dowlex2045G) and two metallocene LLDPEs (AffinityPL1840 and Exact 3128) were blended with a single low‐density polyethylene (LDPE), with all LLDPEs having distinctly different molecular weight. The weight fractions of the LDPEs used in the blends were 1, 5, 10, 20, 50, and 75%. DSC analysis has shown that the blends with metallocence LLDPEs are miscible in the crystal state, whereas for the Ziegler‐Natta, apart from the two distinct peaks of the individual components, a third peak appears which indicates the existence of a third phase that is created from the cocrystallization of components from the two blended polymers. The linear viscoelastic characterization was performed and mastercurves at 150 °C were constructed for all blends to check miscibility using the time temperature superposition principle. In addition, Van Gurp Palmen and zero‐shear viscosity versus composition were constructed to check the thermorheological behavior of all blends. In general, good agreement is found among these various methods. It was concluded that metallocene LLDPEs are more compatible with LDPE at all LDPE compositions when compared with their Ziegler‐Natta counterparts. Finally, the extensional properties of all blends were studied to examine the effects of different levels of LCB on their extensional rheological properties. It was concluded that extensional rheology is a sensitive tool capable of detecting subtle changes in the polyethylene macrostructure, that is, low levels of LCB. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1669–1683, 2008     

Characterization and properties of polyethylene blends II. Linear low-density with conventional low-density polyethylene

Melting and crystallization phenomena in blends of a linear low-density polyethylene (LLDPE) (ethylene butene-1 copolymer) with a conventional low-density (branched) polyethylene (LDPE) are explored with emphasis on composition by differential scanning calorimetry (DSC) and light scattering (LS). Two endotherms are evident in the DSC studies of the blends, which suggests the formation of separate crystals. Light-scattering studies indicate that the blend system is predominantly volume filled by the LLDPE component whereby the LDPE component crystallizes as a secondary process within the domain of the LLDPE spherulites. In contrast to those of the LLDPE/HDPE blends, the mechanical and optical relaxation behavior of the LLDPE/LDPE blends are dominated by the LLDPE component in the vicinities of γ and β regions, whereas the trend reverses at high temperature α regions. This observation is accounted for on the basis of the relative restrictions imposed by the deformation of spherulites (which are primarily made up of the LLDPE component) at different time scales.     

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

Adhesive effect of linear low density polyethylene (LLDPE) gels in organic solvents such as decalin, tetralin, and o-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, and DSC measurements. For all of the gels the temperature at which the heated gel starts to exhibit the adhesive effect was about 70 °C, which is similar to the result of LDPE gel. In particular, when heated at 110 °C, LLDPE gel in tetralin showed such a strong bond strength that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking. It was found that LLDPE gel behaved as though it added LDPE gel to HDPE gel namely LDPE-like components in LLDPE resin exerted the adhesive effect at lower heating temperature, HDPE-like components exerted the strong adhesive effect at higher heating temperature.     

Investigation of polyethylene‐grafted‐maleic anhydride presence as a compatibilizer on various properties of nanocomposite films based on polyethylene/ethylene vinyl alcohol/ nanoclay

High oxygen barrier films were prepared based on low‐density polyethylene (LDPE)/ethylene vinyl alcohol (EVOH)/ nanoclay and polyethylene‐grafted‐maleic anhydride (LDPE‐g‐MA) as a compatibilizer. Box–Behnken statistical experiment design methodology was employed to study the effects of nanoclay, LDPE‐g‐MA, and EVOH presence and their contents on various properties of the final films. The R² parameter varied between 0.89 and 0.99 for all the obtained responses. The morphology of the samples was evaluated. Results of oxygen transfer rate (OTR) test indicated that the addition of EVOH up to 30 wt% to neat LDPE can decrease oxygen permeability significantly. The addition of nanoclay also decreased the permeability of resulting films but, LDPE‐g‐MA reduced the permeability of the films only at an optimal content. Elastic modulus was increased with the addition of nanoclay, EVOH, and LDPE‐g‐MA to the matrix. An increase in EVOH content in the samples improved the tensile strength. Effect of nanoclay on tensile strength was highly dependent on the presence of a compatibilizer. The addition of compatibilizer to the samples and increasing its content enhanced the tensile strength of the specimens. Incorporation of nanoclay, EVOH, and LDPE‐g‐MA to the LDPE matrix and increasing the amount of these components in the samples led to higher storage modulus, zero shear rate viscosity, and shear thinning exponent, but, lowered the terminal slope and the frequency of intersection point of storage modulus (G′) and loss modulus (G″). The only exception was that EVOH increment resulted in a lower shear thinning exponent. Copyright © 2016 John Wiley & Sons, Ltd.     

HDPE,LLDPE或LDPE高取向薄膜微结构的电子显微学研究

木工作用透射电子显微术及电子衍射技术研究3种PE(HDPE,LLDPE或LDPE)均聚物高取向薄膜的微结构。定量测定了它们的结晶尺寸。通过倾斜样品电子显微学研究确定了不同种PE纤维结构的对称性。     

PE/wax blends: interesting observations

The thermal and mechanical properties of different cross-linked and uncross-linked polyethylene/wax blends were investigated over a period of time. This paper summarizes the results and observations. It was found that (i) both LLDPE and LDPE cross-links in the presence of low dicumyl peroxide concentrations, while wax only grafts onto the polyethylene chains, (ii) polyethylene and wax have relatively good miscibility, (iii) both wax content and cross-linking change the mechanical properties of polyethylene in one way or the other, (iv) the route of sample preparation has a marked influence on the thermal and mechanical properties of the blends, and (v) oxygen-containing groups in oxidised wax apparently do not change the way in which the wax interacts with polyethylene.     

Controlled migration of antifog additives from LLDPE compatibilized with LLDPE grafted maleic anhydride

This paper summarizes a study of controlled migration of an antifog (AF) additive; sorbitan monooleate (SMO), from linear low density polyethylene (LLDPE) films containing a compatibilizer, LLDPE grafted maleic anhydride (LLDPE‐g‐MA). LLDPE/LLDPE‐g‐MA/SMO blends were prepared by melt compounding. Bulk and surface properties of compression molded LLDPE films containing SMO and LLDPE‐g‐MA were characterized using Fourier transform infrared spectroscopy and contact angle measurements. Thermal properties were investigated using a thermal gravimetric analyzer. Diffusion coefficient (D) was calculated, and AF properties were characterized using a “hot fog” test. Compression molded films were characterized for their morphology using high‐resolution scanning electron microscopy, and rheological properties were measured using a parallel‐plate rotational rheometer. It was found that the LLDPE/LLDPE‐g‐MA/SMO systems are characterized by a slower SMO migration rate, a lower diffusion coefficient, and lower contact angle values compared with LLDPE/SMO blends. These results are well correlated with results of a hot fog test. Morphological studies revealed a very fine dispersion of SMO in the LLDPE films, when 3 phr LLDPE‐g‐MA was combined with 1 phr SMO. Thermal analysis results show that the incorporation of 3 phr LLDPE‐g‐MA and 1 phr SMO significantly increases the decomposition temperature of the blend at T > 400°C. At high shear rates, the LLDPE blends show that the AF and the compatibilizer have a lubrication effect on LLDPE. Copyright © 2014 John Wiley & Sons, Ltd.     

The compatibilization effect of ethylene/styrene interpolymer on polystyrene/polyethylene blends

In this study, ethylene/styrene interpolymer (ESI) was used as compatibilizer for the blends of polystyrene (PS) and low‐density polyethylene (LDPE). The mechanical properties including impact, tensile properties, and morphology of the blends were investigated by means of uniaxial tension, instrumented falling‐weight impact measurements, and scanning electron microscopy. Impact measurements indicated that the impact strength of the blends increases slowly with LDPE content up to 40 wt %; thereafter, it increases sharply with increasing LDPE content. The impact energy of the LDPE‐rich blends exceeded that of pure LDPE, implying that the LDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of ESI. Tensile tests showed that the yield strength of the PS/LDPE/ESI blends decreases considerably with increasing LDPE content. However, the elongation at break of the blends tended to increase significantly with increasing LDPE content. The compatibilization efficiency of ESI and polystyrene‐hydrogenated butadiene‐polystyrene triblock copolymers (SEBS) for PS/LDPE 50/50 was further compared. Mechanical properties show that ESI is more effective to achieve a combination of LDPE toughness and PS rigidity than SEBS. The correlation between the impact property and morphology of the ESI‐compatibilized PS/LDPE blends is discussed. The excellent tensile ductility of the LDPE‐rich blends resulted from shield yielding of the matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2136–2146, 2007     

Polyethylene‐poly(L‐lactide) diblock copolymers: Synthesis and compatibilization of poly(L‐lactide)/polyethylene blends

A model polyethylene‐poly(L ‐lactide) diblock copolymer (PE‐b‐PLLA) was synthesized using hydroxyl‐terminated PE (PE‐OH) as a macroinitiator for the ring‐opening polymerization of L ‐lactide. Binary blends, which contained poly(L ‐lactide) (PLLA) and very low‐density polyethylene (LDPE), and ternary blends, which contained PLLA, LDPE, and PE‐b‐PLLA, were prepared by solution blending followed by precipitation and compression molding. Particle size analysis and scanning electron microscopy results showed that the particle size and distribution of the LDPE dispersed in the PLLA matrix was sharply decreased upon the addition of PE‐b‐PLLA. The tensile and Izod impact testing results on the ternary blends showed significantly improved toughness as compared to the PLLA homopolymer or the corresponding PLLA/LDPE binary blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2755–2766, 2001     

Effects of poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] on the charge distributions of low‐density polyethylene/polystyrene blends

The effect of the triblock copolymer poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) on the formation of the space charge of immiscible low‐density polyethylene (LDPE)/polystyrene (PS) blends was investigated. Blends of 70/30 (wt %) LDPE/PS were prepared through melt blending in an internal mixer at a blend temperature of 220 °C. The amount of charge that accumulated in the 70% LDPE/30% PS blends decreased when the SEBS content increased up to 10 wt %. For compatibilized and uncompatibilized blends, no significant change in the degree of crystallinity of LDPE in the blends was observed, and so the effect of crystallization on the space charge distribution could be excluded. Morphological observations showed that the addition of SEBS resulted in a domain size reduction of the dispersed PS phase and better interfacial adhesion between the LDPE and PS phases. The location of SEBS at a domain interface enabled charges to migrate from one phase to the other via the domain interface and, therefore, resulted in a significant decrease in the amount of space charge for the LDPE/PS blends with SEBS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2813–2820, 2004     

Influence of the molecular architecture of low‐density polyethylene on the texture and mechanical properties of blown films

Three types of low‐density polyethylene materials were investigated with respect to the influence of the molecular architecture on the mechanical and use properties of blown films. The materials were a branched polyethylene synthesized by free‐radical polymerization under high‐pressure (HP‐LDPE), a linear ethylene–hexene copolymer (ZN‐LLDPE) produced by low‐pressure Ziegler–Natta catalysis, and an ethylene–hexene copolymer (M‐LLDPE) from metallocene catalysis. The extrusion and blowing conditions were identical for the three materials, with a take‐up ratio of 12 and a blow‐up ratio of 2.5. The blown films displayed a decreasing puncture resistance in the order M‐LLDPE, ZN‐LLDPE, and HP‐LDPE. In parallel, the tear resistance of the films became increasingly unbalanced in the same order of the polymers. The morphological study showed an increased anisotropy of the films in the same polymer order, the crystalline lamellae being increasingly oriented normal to the take‐up direction. This texturing caused a detrimental effect on the mechanical properties of the films, notably increasing the capacity for crack propagation. The phenomenon was ascribed to the kinetics of chain relaxation in the melt that governed the ability of the chains to recover an isotropic state from the flow‐induced stretching before crystallization. The puncture resistance was examined in terms of both texture and strain‐hardening capabilities. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 327–340, 2003     

Effect of LDPE on the thermomechanical properties of LLDPE‐based films

The present study compares the properties of five films: one film of low‐density polyethylene (LDPE), two films of linear low density polyethylenes (1‐octene comonomer)—one made by metalllocene catalyst (mLLDPE) and the other by Ziegler–Natta (zLLDPE)—and two blend films, one of mLLDPE/LDPE (film A) and the other of zLLDPE/LDPE (film B). The effect of LDPE (22% by weight) on the thermomechanical properties of LLDPE‐based films is investigated by using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and stress‐strain in the yield region measurements. The mechanical, dynamic, and thermal properties of film A are quite similar to a single component system (mLLDPE). The addition of this amount of LDPE does not affect the melting temperature of mLLDPE but it enhances its crystallinity. Film B is a rather inhomogeneous material, as opposed to film A, and its properties seem to be dependent on stretching conditions. Furthermore, the thermally activated rate process (Eyring's theory) is applied to analyze the yielding behavior of the two blend films. Double yielding manifested by film B is described with two thermally activated processes, while film A is satisfactorily described by a single process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1712–1727, 2005     

Linear low‐density polyethylene nanocomposites by in situ polymerization using a zirconium‐nickel tandem catalyst system

A series of linear low‐density polyethylene (LLDPE) nanocomposites containing different types of nanofiller (TiO₂, MWCNT, expanded graphite, and boehmite) were prepared by in situ polymerization using a tandem catalyst system composed of {Tp^Ms}NiCl ( 1 ) and Cp₂ZrCl₂ ( 2 ), and analyzed by differential scanning calorimetry, dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). Based on these analyses, the filler content varied from 1.30 to 1.80 wt %. The melting temperatures and degree of crystallinity of the LLDPE nanocomposites were comparable to those of neat LLDPE. The presence of MWCNT as well as boehmite nucleated the LLDPE crystallization, as indicated by the increased crystallization temperature. The DMA results showed that the presence of TiO₂, EG, and CAM 9080 in the LLDPE matrix yielded nanocomposites with relatively inferior mechanical properties compared to neat LLDPE, suggesting heterogeneous distribution of these nanofillers into the polymer matrix and/or the formation of nanoparticle aggregates, which was confirmed by TEM. However, substantial improvement in the storage modulus was achieved by increasing the sonication time. The highest storage modulus was obtained using MWCNT (1.30 wt %). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3506–3512     

Preparation and characterization of glass fiber–reinforced polyethylene terephthalate/linear low density polyethylene (GF‐PET/LLDPE) composites

Polyethylene terephthalate (PET) was melt blended with linear low density polyethylene (LLDPE) and subsequently compounded with glass fibers (GF) as reinforcements at percentages ranging from 15 to 45 wt% of LLDPE and 5 to 30 wt% of GF. Thermal, morphological, and mechanical properties of the prepared composites were investigated. It was found that compounding PET/LLDPE blends with GF would be beneficial in producing composites that are thermally stable with good mechanical properties. For example, the impact strength of the composites containing 85/15 wt% (PET/LLDPE) at relatively high loading of GF, ie, from 15 to 30 wt%, was higher than that of the GF‐reinforced neat PET. When increasing the percentage of LLDPE in the composites, the impact strength increased with increasing GF content, and this was also better than that of GF‐reinforced PET whose impact strength drastically decreased upon increasing the GF%. The improvement in mechanical properties of the composite, we suggest, should be correlated with the morphologies of the composites where the visualized interface adhesion tended to be better at higher loadings of both LLDPE and GF.     

Migration phenomena of surfactants in polyethylene film

Migration diffusion coefficients of two surfactants (sorbitan laurate, SPAN‐20 and sorbitan palmitate, SPAN‐40) in polyethylene blend are calculated in the desorption process by means of Fourier transform infrared (FT‐IR) spectroscopy technique at 25°C. They are 2.31 and 2.24 × 10⁻¹¹ cm²/s, respectively, which show no significant dependency of molecular weights of the surfactants on diffusion. The composition of LLDPE (linear low‐density polyethylene) and LDPE (low‐density polyethylene) in LLDPE blend is a 7 : 3 ratio, and ethylene acrylic acid (EAA) copolymer is used to verify its role as a migration controller. The key factor affecting the diffusion of the surfactant is suggested to be the segmental mobility by the semicrystalline LLDPE blend. Incorporation of 20 wt% EAA in the LLDPE blend retards the migration rate of the surfactants by reducing the diffusion coefficients to be 9.6 and 7.7 × 10⁻¹² cm²/s and this is believed to be due to the blocking effect of EAA. Although the diffusion coefficient was varied from system to system, the migration kinetics of the surfactants in short times obeys the Fickian behavior if the experimental error is allowed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1387–1395, 1999     

Natural weathering test for films of various formulations of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)

Natural (outdoor) weathering test was performed to investigate the UV stability of thin films (0.06 mm) of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). The PE films were prepared from various formulations of LLDPE and LDPE resins. Some of these films contained a single high molecular mass HALS only, along with a primary antioxidant (i.e. Irganox 1010) and a secondary antioxidant (i.e. Irgafos 168 or Alkanox TNPP), while others contained HALS and UVA (i.e. Chimassorb 81 or Tinuvin P or Tinuvin 326) along with these antioxidants. The HALS used was either an oligomeric or a synergistic mixture of a high molecular mass (HMM) hindered amine stabilizer and co-additives. The UV stability was investigated by exposing the prepared films at 45° towards south in the direct sunshine up to 365 days. Fifty percent of tensile strength retention was determined for all these exposed films and it was found that the films containing a single HALS gained improved UV stability by about two to 12 fold over the pure films. On the other hand, films that contained a combination of HALS and UVA obtained further improved UV stability over the films containing a single HALS (both have antioxidants). Films containing a single HALS reached 50% TS retention within 205 days, whereas, films containing a combination of HALS and UVA reached 50% TS retention within 590 days, which is about three times further improvement in UV stability.