Linear Low-density Polyethylene Content Research Articles

Ultraviolet light irradiated high‐efficiency crosslinking and insulating properties of LLDPE/EPDM blends

AbstractUltraviolet light (UV) irradiation crosslinked linear low‐density polyethylene (LLDPE)/ethylene propylene diene monomer (EPDM) composites with different blending ratios were prepared using benzophenone (BP) as photoinitiator and triallyl isocyanurate (TAIC) as crosslinking agent. The irradiation time was determined, the effects of rubber‐plastic ratio on the crystallization behaviors, mechanical properties, crosslinking properties and electrical properties of LLDPE/EPDM composites were investigated. The results show that with the increase of EPDM content, the crystalline structure of LLDPE/EPDM composite become looser and the crystallinity decreased. The blending of EPDM and LLDPE results in two different aggregation states of the same crystalline form. With the increase of LLDPE content, the crosslinking efficiency, tensile strength, and energy storage modulus show a significant upward trend. When two polymers simultaneously exist in the material, if the difference between the contents of two polymers is large, the breakdown strength of the composite is relatively lower. The relaxation polarization of LLDPE/EPDM at low frequencies increases with the content of EPDM, thus leading to the increase of loss factor at low frequencies. A novel UV crosslinked modified EPDM insulating material with high production efficiency and improved insulation performances has been developed for use as an insulating layer for flexible power cables.

Manufacturing Pitch and Polyethylene Blends-Based Fibres as Potential Carbon Fibre Precursors.

The advantage of mesophase pitch-based carbon fibres is their high modulus, but pitch-based carbon fibres and precursors are very brittle. This paper reports the development of a unique manufacturing method using a blend of pitch and linear low-density polyethylene (LLDPE) from which it is possible to obtain precursors that are less brittle than neat pitch fibres. This study reports on the structure and properties of pitch and LLDPE blend precursors with LLDPE content ranging from 5 wt% to 20 wt%. Fibre microstructure was determined using scanning electron microscopy (SEM), which showed a two-phase region having distinct pitch fibre and LLDPE regions. Tensile testing of neat pitch fibres showed low strain to failure (brittle), but as the percentage of LLDPE was increased, the strain to failure and tensile strength both increased by a factor of more than 7. DSC characterisation of the melting/crystallization behaviour of LLDPE showed melting occurred around 120 °C to 124 °C, with crystallization between 99 °C and 103 °C. TGA measurements showed that for 5 wt%, 10 wt% LLDPE thermal stability was excellent to 800 °C. Blend pitch/LLDPE carbon fibres showed reduced brittleness combined with excellent thermal stability, and thus are a candidate as a potential precursor for pitch-based carbon fibre manufacturing.

Rheological properties of high-density polyethylene/linear low-density polyethylene and high-density polyethylene/low-density polyethylene blends

In this work, the effect of the linear low-density polyethylene (LLDPE) containing 1-butene or 1-hexene α-olefin short-chain branching (SCB) and low-density polyethylene (LDPE) containing long-chain branching (LCB) on the rheological properties of high-density polyethylene (HDPE)/LLDPE and HDPE/LDPE blends was investigated. The neat polymers and the blends were characterized by torque rheometry and rheological measurements under dynamic oscillatory shear flow. From torque rheometry analysis, an increase in the viscosity of HDPE/LLDPE blends with the increase in LLDPE content was observed. The inverse was observed for HDPE/LDPE blend, where the viscosity decreased with the increase in the LDPE content. Rheological measurements showed an increase in the complex viscosity of the HDPE/LLDPE and HDPE/LDPE blends with the increase in the LLDPE or LDPE content. HDPE/LDPE blends showed a strong shear-thinning behavior due to the presence of LCB in LDPE. Similar rheological behavior was observed for HDPE/LLDPE blends containing 1-butene and 1-hexene SCB. Cole–Cole, Han plots, and van Gurp–Palmen plots indicated miscibility between HDPE and LLDPE and immiscibility between HDPE and LDPE.

Evaluating melt foamability of LLDPE/LDPE blends with high LLDPE content by bubble coalescence mechanism

Bubble coalescence mechanism was introduced to evaluate the melt foamability of polymer blends. Linear low-density polyethylene (LLDPE), with excellent mechanical properties but poor foamability, was blended with small amounts of low-density polyethylene (LDPE), which was expected to impart the desired foaming-related properties to LLDPE. The presence of LDPE in LLDPE matrix provided only a small improvement in linear viscoelasticity under small deformations, but a significantly large improvement in nonlinear behavior under large deformations. A critical coalescence radius curve was simulated using a pressure-balanced bubble growth model to evaluate bubble coalescence and foamability of the blends, taking into account the linear and non-linear behaviors. It was found that the steep stress growth caused by LDPE addition can dramatically increase the pressure of large bubbles and then effectively inhibit the coalescence of adjacent bubbles, thus improving the foamability of LLDPE/LDPE blends. The theoretical predictions derived from the bubble coalescence mechanism were also confirmed by experiments.

Rheological aspects and film processability of poly (lactic acid)/linear low‐density polyethylene blends

AbstractPoly (lactic acid) (PLA) and Linear low‐density polyethylene (LLDPE) were compounded in a corotating twin screw extruder. PE‐g‐glycidyl methacrylate was also added as a reactive compatibilizer in PLA/LLDPE blend system, which lowered interfacial tension between PLA and LLDPE. Blown films were prepared by using a single‐screw extruder for all compounded blends. The investigation of the rheological properties of a polymeric system is very important to study the processability and understand structure‐property relationship in blown films. In the present research work, the rheological properties have been investigated to assess the processability of blown films of PLA/LLDPE blends. Oscillatory shear rheology viscoelastic spectra showed an increase in the storage and loss moduli with the increase in LLDPE and compatibilizer content, which indicated pronounced viscoelastic behavior of PLA with the addition of LLDPE and compatibilizer. A steady increase in the value of extensional viscosity as a function of time was observed with the addition of LLDPE and compatibilizer in PLA. The blends with higher LLDPE content exhibited much more prominent strain hardening characteristics than those with lower LLDPE content.

Study on properties and stress relaxation behavior of oil‐extended SBS/LLDPE/EVA blends

ABSTRACTIn order to explore and develop a new sealing material, the oil‐extended styrene‐butadiene‐styrene (SBS)/Linear low density polyethylene (LLDPE)/ethylene‐vinyl acetate (EVA) blends were prepared by melt mixing method and the effects of components on mechanical, rheological properties, and microstructure of the blends were investigated. The results showed that the resilience of the blends was barely changed during three‐time cyclic compression. The increase of oil‐extended SBS content would reduce the hardness of the blends as well as its compatibility and increase the melt flow rate. An increase in the LLDPE content, however, has the opposite effect on the blends. In contrast, EVA has little effect on the mechanical and rheological properties of the blends, but its addition could improve the transparency of samples effectively while promote the phase separation of the sample and complicate its microstructure. The master curve of stress relaxation modulus obtained by time–temperature superposition principle could be used to predict the long‐term (1.5 × 108 s, about 4.7 years) stress relaxation behavior of the blends at room temperature while the correlation coefficient of the shift factor fitting is 0.987. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48930.

A polyolefin encapsulant material designed for photovoltaic modules: from perspectives of peel strength and transmittance

A secondary master batch process had been applied to design a polyolefin encapsulant material for photovoltaic modules, in which the polymer blend was composed of polyolefin elastomer (POE) and linear low-density polyethylene (LLDPE) with the addition of the cross-linking agent of tert-butylperoxy 2-ethylhexyl carbonate (TBEC) and silane coupling agent of γ-methacryloxypropyl trimethoxy silane (KH570). The rheological property from Haake torque rheometer illuminated that the chemical cross-linking reaction could take place between the POE and TBEC. The LLDPE was added for further increasing the cohesion of polymer blend by obtaining much more physical cross-linking points from the physical entanglement between the flexible chains of LLDPE and the amorphous zone of POE. However, the transmittance of polymer blend ran down with the rise of LLDPE content within the polymer blend. The number and site of melting points of polymer blend by the DSC analysis show that there was compatibility between the POE and LLDPE within the polymer blend; meanwhile, the resultant molecular structures of the polymer blend also had been explained by the FTIR spectra. These results unanimously illuminated that it was a feasible solution for fabricating the polyolefin encapsulant material for photovoltaic modules.

Linear low‐density polyethylene/poly(ethylene terephthalate) blends compatibilization prepared by an eccentric rotor extruder: A morphology, mechanical, thermal, and rheological study

ABSTRACTIn this study, various poly(ethylene terephthalate) (PET) and linear low‐density polyethylene (LLDPE) with maleic anhydride‐grafted LLDPE (LLDPE‐g‐MAH) compatibilizer were melt blended under an elongational flow. A novel extrusion device, eccentric rotor extruder (ERE), was developed to supply such flow during the process. Including morphology, mechanical properties, melting behavior, and rheological behavior were studied. The morphological study showed that the compatibility between LLDPE and PET was greatly improved with LLDPE loading up to 80 wt %. Mechanical tests indicated that LLDPE could toughen PET to some extent. Moreover, a comparison of samples prepared between ERE and conventional extruder was made and demonstrated the sample prepared by ERE can exhibit better mechanical properties. Differential scanning calorimetry results revealed that PET can promote the crystallinity of LLDPE. Rheological behavior indicated that the complex viscosity of the blends exhibited strong shear thinning phenomenon with increasing LLDPE content, particularly in high‐frequency range blend with the LLDPE weight ratio of 80 wt % was more sensitivity to shear rate than neat LLDPE. The G′‐G″ curves of the blends also revealed that the microstructure of the blends changed significantly with the addition of LLDPE which was consistent with the scanning electron micrographs that PET particles became smaller and distributed more uniform with increasing LLDPE content. Furthermore, the blends showed similar stress relaxation mechanism with adding LLDPE content from 60 to 100 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46489.

THE INFLUENCE OF POLYMER ON RHEOLOGICAL AND THERMO OXIDATIVE AGING PROPERTIES OF MODIFIED BITUMEN BINDERS

Polymer modified bitumen (PMB) has been used for many years to improve the performance of asphalt concretes against premature pavement defects. In this research, modified samples were prepared with 2%, 3%, 4%, 5% and 6% Linear Low Density Polyethylene (LLDPE) polymer by weight of bitumen binder. The influence of LLDPE polymer was evaluated through binder properties test which includes penetration, softening point, storage stability, temperature susceptibility, rutting, fatigue and thermal oxidative aging resistance from a dynamic shear rheometer (DSR) measurements at a temperature of 20 OC to 60 OC. Results show that LLDPE polymer has a significant effect on binder properties. Penetration decreases and softening point increases with increasing LLDPE content on the modified binder after aging, which implies LLDPE improves the thermo oxidative aging resistance of the binder. Furthermore, the storage stability test shows that at higher LLDPE concentrations phase separation may occur. DSR analysis shows that modified binders have lower temperature susceptibility and higher aging resistance with increased stiffness and elastic behavior compared with unmodified binders. In addition, modified binders show enhanced resistance against high temperature rutting and at low temperature fatigue performance. It was found that the optimum LLDPE content is 6%.

Predicting of mechanical properties of PP/LLDPE/TiO2 nano-composites by response surface methodology

The object of this work is to study the mechanical properties of ternary nano-composites based on polypropylene/linear low density polyethylene/nano-titanium dioxide (PP/LLDPE/TiO2) using the response surface methodology (RSM). Experiments were designed according to a Box–Behnken method, to quantify the effects of linear low density polyethylene (LLDPE), styrene–ethylene–butylene–styrene (SEBS as a compatibilizer), and titanium dioxide (TiO2) nano-particles. Three levels were chosen for the considered parameters as follows: LLDPE (20–60 wt%), TiO2 (0–4 wt%), and SEBS (0–6 wt%). In addition, RSM models were used to develop the desirability function. Finally, the morphology and thermal properties of the samples were evaluated by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). It was found that the LLDPE content had the main role in mechanical properties and morphology of the nano-composite. The optimal values of the nano-particle were predicted to be 24.85 wt% for LLDPE, 3.02 wt% for TiO2, and 6 wt% for SEBS. The obtained R2 values and normal probability plots indicated a good agreement between the experimental results and those predicted by the model (above 0.95 for all the responses).

Calendered linear low‐density polyethylene consolidated meat and bone meal composites

ABSTRACTBioplastics produced from meat and bone meal (MBM) suffer from rapid and drastic mechanical property deterioration because of their hydrophilic nature. This study investigates mechanical and water stability of composites produced from introduction of a minor component of a synthetic polyethylene as a binder phase to consolidate MBM. The milled and sieved MBM was compounded with 5–60 wt % linear low‐density polyethylene (LLDPE) and formed into composite sheets by calendering, which is an industrially relevant process. Results indicated that a minimum of 15 wt % LLDPE content was required to form a nominally continuous binder phase that allowed for good processability and environment stability of the composites. As expected, the water vapor permeability (WVP) and water absorption characteristics of the composites were intermediate between those of MBM and LLDPE. Sheets containing 15 wt % LLDPE absorbed up to 35 wt % water. Composites tested after being soaked in water showed an initial decrease in TS of about 30% for the first hour but then remained fairly unchanged in the next 72 hours, confirming their moderate environment stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41145.

Mechanical and shape memory behavior of chemically cross-linked SBS/LDPE blends

A series of polymeric shape memory system of chemically cross-linked poly(styrene-b-butadiene-b-styrene) triblock copolymer(SBS) and linear low density polyethylene(LDPE) blends were developed and characterized. The chemically cross-linked SBS/LDPE blends were prepared by varying the amount of initiator (DCP) between 0 and 1.5 wt.% and the ratio of SBS/LDPE ranges from 90/10 to 60/40. The cross-linked SBS/LDPE blends were fully characterized by gel content, tensile test, dynamic mechanical analysis (DMA), differential scanning calorimeter (DSC) and shape memory behavior. Results demonstrate that the cross-linking degree increases with the increment of the DCP content, leading to reductions in tensile strength and elongation at break. The transition temperature of cross-linked SBS/LDPE blends is tunable through changing SBS/LDPE ratio and DCP content. DMA test shows that the melt strength of the blends is influenced by the DCP and LDPE content. The chemically cross-linked SBS/LDPE blends have excellent shape memory effect when the cross-linking degree between 46 and 77 %. The shape recovery time decreases as the test temperature increases and the shape recovery rate decreases with cycle times increasing.

Mechanical strengths of molten and solidified LLDPE/LDPE blends and wood/LDPE composites under tensile deformation

AbstractThe mechanical strengths of neat low‐density polyethylene (LDPE), a blend of LDPE with linear low‐density polyethylene (LLDPE), and a composite of LDPE with wood flour (wood/LDPE) were investigated in molten and solidified states under tensile deformation. The results are discussed in terms of the effects of LLDPE and wood contents, roller speed, and volumetric flow rate. In LLDPE/LDPE blends, incorporating LLDPE from 0 to 30 wt% into LDPE caused a slight increase in drawdown force, a larger fluctuation in drawdown force, and a reduction of maximum roller speed to failure. The mechanical properties of the solidified LLDPE/LDPE corresponded to those of the molten LLDPE/LDPE with regard to the effect of LLDPE content. For wood/LDPE composites, increasing the wood flour content in molten LDPE caused considerable reductions in drawdown time and maximum roller speed to failure. The drawdown force increased with increasing wood flour up to 10 wt% before it decreased at the wood loading of 20 wt%. A number of voids and pores on the extrudate surfaces became obvious for the composites with 20 wt% of wood content. Increasing wood content enhanced the tensile modulus for the solidified LDPE but decreased its tensile strength. Unlike those of LLDPE/LDPE blends, the changes in tensile modulus and strength of solidified wood/LDPE composites with wood content did not correspond to those of the molten composites. In all cases, the drawdown force increased with increasing roller speed. The effect of volumetric flow rate from the extruder on the mechanical strengths of the solidified blends was more pronounced than on those of the molten ones. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers

Mechanical and thermal properties of calcium carbonate‐filled PP/LLDPE composite

AbstractPolymer blends typically are the most economical means to develop new resins for specific applications with the best cost/performance balance. In this paper, the mechanical properties, melting, glass transition, and crystallization behavoir of 80 phr polypropylene (PP) with varying weights of linear low density polyethylene (LLDPE) at 10, 20/ 20 wt % CaCO3, 30, 40, and 50 phr were studied. A variety of physical properties such as tensile strength, impact strength, and flexural strength of these blends were evaluated. The compatibility of these composite was examined by differential scanning calorimetry (DSC) to estimate Tm and Tc, and by dynamic mechanical analysis (DMA) to estimate Tg. The fractographic analysis of these blends was examined by scanning electron microscopy (SEM). It has been confirmed that increasing the LLDPE content trends to decreases the tensile strength and flexural strength. However, increasing the LLDPE content led to increases in the impact strength of PP/LLDPE blends. It was also found that up to 40 phr the corresponding melting point (Tm) was not effected with increasing LLDPE content. Each compound has more than one Tg, which was informed that there is a brittle‐ductile transition in fracture nature of these blends, the amount of material plastically deformed on the failure surface seems to increase with the increasing the LLDPE content. And PP/LLDPE blends at temperature (23°C) showed a ductile fracture mode characterized by the co‐existence of a shear yielding process; whereas at lower temperature (−20°C) the fractured surfaces of specimens appear completely brittle. The specimens broke into two pieces with no evidence of stress whitening, permanent macroscopic deformation or yielding. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal Analysis Studies of (Bi, Pb)-2223/Linear Low Density Polyethylene Composite Materials

Series of superconductor/polymer composites were prepared using high-temperature superconductor Bi1.8Pb0.4Sr2Ca2.1Cu3.2O10+δ phase and linear low density polyethylene (LLDPE). The LLDPE concentration varied from 0.0 to 100 wt. % of the sample’s total mass. The composite materials were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), whereas the crystallization point of LLDPE and its composites were determined using differential scanning calorimetery (DSC). Furthermore, the thermal expansion measurements for composite materials were taken from room temperature up to 160 °C. The results showed that the thermal expansion coefficient increased with increasing of the percentage of LLDPE content.

Orientation and Epitaxy in the Injection-Molded Bars of Linear Low-Density Polyethylene/Isotactic Polypropylene Blends: An Infrared Dichroism Measurement

In this article, molecular orientation of crystalline and amorphous phases of both linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) and epitaxy in the LLDPE/iPP blends prepared via dynamic packing injection molding have been investigated with the aid of polarized Fourier transform infrared (FTIR) spectroscopy and two-dimensional X-ray scattering (2D-WAXS). In LLDPE-rich blends, LLDPE was oriented along the shear flow direction, and iPP kept very low orientation. No epitaxial growth between LLDPE and iPP was observed. However, for the blends with LLDPE content less than 50 wt %, where iPP was the matrix and LLDPE formed the droplets, iPP was highly oriented along shear flow direction and LLDPE epitaxially grew onto iPP. The contact planes were (100)LLDPE and (010)iPP, and LLDPE molecules were about 50 degrees apart from the shear direction. The epitaxy fraction in LLDPE/iPP blends could be tentatively calculated from the values of orientation function of the LLDPE crystalline a-axis (fa) and that of crystalline b-axis (fb). Both tensile strength and tensile modulus decreased with the increase of LLDPE composition, indicating they were composition dependent, though shear-induced orientation and epitaxial crystallization might play some role. The impact strength of the blend samples reached a plateau in the LLDPE composition range of 20-50%, due to the contribution of orientation and epitaxy.

Miscibility in crystalline polymer blends: Isotactic polypropylene and linear low‐density polyethylene

AbstractThe phase behavior and the crystallization kinetics of blends composed of isotactic polypropylene (iPP) and linear low‐density polyethylene (LLDPE) were investigated by differential scanning calorimetry. The phase behavior indicates the formation of separate crystals of iPP and LLDPE at each investigated blend composition. The crystallization trace reveals that iPP crystallizes in its normal range of temperatures (i.e., at temperatures higher than that of LLDPE), when its content in the blend is higher than 25% by weight. In the blend whose iPP content is as high as 25%, at least a portion of iPP crystallizes at temperatures lower than that of LLDPE. This behavior has been proposed by Bassett to be attributed to a change in the kind of nucleation from heterogeneous to homogeneous. From the Avrami analysis of the isothermal crystallization of iPP in the presence of molten LLDPE, n values close to 2 are always obtained. According to our previously proposed interpretation of the Avrami coefficient, it can be related to the crystallite fractal dimension, through d = n + 1, which gives values close to 3, according to the spherulitic observed morphology. The kinetics parameter, i.e., the half‐time of crystallization, and the kinetic constant k show that a decrease in the overall rate of crystallization of iPP occurs on blending. Optical microscopy photographs, taken during the cooling of the samples from the melt, confirm the above results and show increasingly less resolved spherulite texture on increasing LLDPE content in the blend. The diffusion parameters evaluated for the neat polymers and for the blends in dichloromethane, which give information on the miscibility in the amorphous state, show that the diffusional behavior of the blends is governed by iPP, suggesting a two‐phase amorphous state. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3338–3346, 2003

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

AbstractThis 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

Properties of films made from ternary blends of metallocene and conventional polyolefins

AbstractThin films were blown from a composition of 75% linear low density polyethylene (LLDPE) and 25% LDPE. The LLDPE content was made up of different % of metallocene‐based and conventional octene‐based LLDPE. Tensile strength, dart impact strength, hot tack strength, heat seal strength, and the barrier properties of these films were measured. All the properties showed significant improvement when conventional LLDPE (cLLDPE) was replaced by metallocene‐based LLDPE (mLLDPE), even to the extent of only 25%. The blends of 50% mLLDPE and 50% LDPE showed attractive properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 53–57, 2001

White Rice Husk Ash Filled Natural Rubber/Linear Low Density Polyethylene Blends

Natural rubber (NR)/Linear low density polyethylene (LLDPE) blends were prepared using an internal mixer at 150°C and a rotor speed of 55 rpm. The tensile strength, tensile modulus and hardness increase with increasing LLDPE content whereas elongation at break and mass swell show decreasing trend. With 30/70 (W/W) NR/LLDPE blends, the increasing white rice husk ash (WRHA) loading also increases the tensile modulus and hardness but reduced the tensile strength, elongation at break, and mass swell.