Crystallinity Of Low-density Polyethylene Research Articles

Recalibrating polyparameter linear free energy relationships and reanalyzing mechanisms for partition of nonionic organic compounds to low-density polyethylene passive sampler

Equilibrium passive sampling techniques based on the low-density polyethylene (LDPE) film are increasingly used for determining the concentration of contaminants in water and air. Reliable models capable of predicting LDPE–water and LDPE–air partition coefficients (KiLDPEw and KiLDPEa) would be very useful. In previous studies, polyparameter linear free energy relationships (PP-LFERs) based on Abraham's solute descriptors were calibrated for LDPE–water and LDPE–air systems. Unfortunately, a portion of unreliable partition coefficients and solute descriptors were included in the calibration sets of these previous studies, leading to unexpected system parameters and predictive performance in the regression results. In this study, more reliable PP-LFERs were recalibrated for LDPE–water and LDPE–air systems (20‒25 °C) using carefully collected reliable partition coefficients and solute descriptors of various polar and nonpolar compounds (over one hundred and with low redundancy) from the literature, as well as the robust regression method. The PP-LFERs performed well with root-mean-square errors of 0.15–0.25 log units and successfully predicted KiLDPEw and KiLDPEa values spanning over 10 orders of magnitude for compounds with reliable descriptors. The partitioning mechanisms of compounds to LDPE were also reanalyzed and compared in detail with n-alkanes (C6–C16). Generally, LDPE is more prone to form dispersion interactions with solutes than n-alkanes, while it is more difficult to form cavities in LDPE. In addition, the crystallinity of LDPE is not the sole reason for the distinct constant terms presenting in PP-LFERs for LDPE–water and n-hexadecane–water systems.

Constructing stable “bridge” structures with compatibilizer POE‐g‐GMA to improve the compatibility of starch‐based composites

AbstractWith the development of degradation technologies such as chemical‐catalysis and bio‐catalysis, starch‐polyethylene (PE) composites have been revitalized as industrial packaging materials. However, starch and PE suffer from interfacial incompatibility. In this study, poly(octene ethylene) grafted glycidyl methacrylate (POE‐g‐GMA) was added at relatively low amounts (0–7 wt%) to construct robust structures between thermoplastic starch (TPS) and low‐density polyethylene (LDPE). Tensile strength increased by 36.39% with the addition of 1 wt% POE‐g‐GMA. Meanwhile, a smooth surface was observed by SEM, and a fibrillar cross‐linked structure appeared on the fractural surface of the blend. POE‐g‐GMA formed a stable “bridge” at the interface between TPS and LDPE, which increased the thermal stability of the blend as well. The crystallinity of LDPE increased from 20.5% (without addition) to 32.8% (with 1 wt% addition), whereas the average crystallite size decreased slightly. The optimal POE‐g‐GMA content was found to be 1 wt% based on mechanical and thermal measurements. The results of this study can provide a reference for improving the interfacial compatibility of biopolymers and fossil‐fuel‐based polymers.

Reusing Surlyn® Ionomer Scraps in LDPE Blends: Mechanical and Thermal Properties

This study aimed to evaluate the possibility of reusing industrial scraps of Surlyn® ionomer by obtaining blends with Low-Density Polyethylene (LDPE). Blends of LDPE and Surlyn® scraps were obtained by extrusion with compositions ranging from 25 to 75 wt% of the ionomer. Their melt flow index (MFI), morphology (SEM), mechanical (tensile, flexural, impact tests) and thermal properties (DSC, TGA, HDT tests) were analyzed. The morphology of the blends presented two phases, indicating the immiscibility of phases. Surlyn® incorporation promoted a decrease in the degree of crystallinity of LDPE and a slight increase in the thermal decomposition temperature. In addition, Surlyn® decreased the decomposition rate of LDPE. However, the decrease in the degree of crystallinity did not affect the mechanical properties of the blends. Incorporating ionomer in LDPE promoted an increase in tensile and flexural strength, tensile and flexural modulus and strain at break. Impact strength decreased with increasing ionomer concentration.

The effect of peroxide cross-linking on the thermal conductivity and crystallinity of low-density polyethylene

In this work, the thermal conductivity of a series of low-density polyethylene (LDPE) with different degrees of cross-linking was measured by the transient hot-wire method at different temperatures. It was found that the thermal conductivity of LDPE samples with different degrees of cross-linking decreased smoothly with increasing temperature at temperatures ranging from ‐20 to 80°C. The higher the degree of cross-linking, the smaller the negative temperature dependence of the cross-linked LDPE samples. The decrease of negative temperature dependence of LDPE was explained by the thermal vibration of molecular chains. Meanwhile, the crystallinity and melting point of a series of LDPE samples with different degrees of cross-linking were determined by differential scanning calorimetry (DSC), and the crystallization process of LDPE samples with different degrees of cross-linking was investigated using the Jeziorny method with a modification of the Avrami equation. The results show that the thermal conductivity of cross-linked LDPE is directly proportional to the crystallinity and inversely proportional to the gel content. This work provides a basis for the future design of semi-crystalline polymers with no temperature dependence of thermal conductivity.

Investigation of Electrical Properties of BiFeO3/LDPE Nanocomposite Dielectrics with Magnetization Treatments.

The purpose of this paper is to study the effect of nano-bismuth ferrite (BiFeO3) on the electrical properties of low-density polyethylene (LDPE) under magnetic-field treatment at different temperatures. BiFeO3/LDPE nanocomposites with 2% mass fraction were prepared by the melt-blending method, and their electrical properties were studied. The results showed that compared with LDPE alone, nanocomposites increased the crystal concentration of LDPE and the spherulites of LDPE. Filamentous flake aggregates could be observed. The spherulite change was more obvious under high-temperature magnetization. An agglomerate phenomenon appeared in the composite, and the particle distribution was clear. Under high-temperature magnetization, BiFeO3 particles were increased and showed a certain order, but the change for room-temperature magnetization was not obvious. The addition of BiFeO3 increased the crystallinity of LDPE. Although the crystallinity decreased after magnetization, it was higher than that of LDPE. An AC test showed that the breakdown strength of the composite was higher than that of LDPE. The breakdown strength increased after magnetization. The increase of breakdown strength at high temperature was less, but the breakdown field strength of the composite was higher than that of LDPE. Compared with LDPE, the conductive current of the composite was lower. So, adding BiFeO3 could improve the dielectric properties of LDPE. The current of the composite decayed faster with time. The current decayed slowly after magnetization.

Controlled-release of ferulic acid from active packaging based on LDPE/EVA blend: Experimental and modeling

Abstract In this study, low-density polyethylene (LDPE) and ethylene vinyl acetate copolymer (EVA), as non-polar and polar polymers, were blended with ferulic acid (FA) as natural antioxidant at various compositions to make active packaging films with a controlled release of FA characteristic. The phase behavior of the blends studied by scanning electron microscopy revealed matrix-droplet morphology in blend containing 10 and 30 wt.% EVA, while the morphology was seen to be co-continuous in the 50/50 composition. Based on the differential scanning calorimetry results a reduction in the crystallinity of LDPE with narrow crystallite size distribution was observed on increasing the EVA content of the blends. The release rate of FA from the LDPE/EVA films was measured by means of UV–vis spectrophotometry and the results were compared with the release behavior of the neat LDPE and EVA as reference materials. It was found that by applying the second Fick’s law the diffusion coefficient of EVA film against FA is 635 times greater than that of LDPE. The blends exhibited a better release behavior as compared to the neat polymers. The best and sustainable release behavior was obtained for the films with 30 wt. % of EVA content in which the FA was released in the environment with a controlled rate. Finally, the series, parallel, Maxwell and Equivalent Box Models (EBM) were applied to investigate the diffusivity coefficient of the blends. The EBM model showed the best agreement with the experimental data.

Effect of particle size distribution on thermo-mechanical properties of NiO filled LDPE composites

The effect of nickel oxide (micro) addition on thermo-physical and mechanical properties of low density polyethylene (LDPE) has been studied. The samples have been prepared by the melt mixing process. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) of the samples have been performed for micro-structural characterization and surface morphology, respectively. The XRD result confirms that the crystallinity of LDPE is affected by NiO addition, whereas the agglomeration of nickel oxide can be seen in the SEM photographs of LDPE samples having higher NiO loading. The thermal stability of the samples has been checked from DSC and TGA analyses under nitrogen atmosphere. The thermal stability of LDPE improves with the addition of a small amount of NiO particles. However, the peak melting temperature of LDPE/NiO composites decreases due to the dispersion of nickel oxide in the LDPE matrix. Again, the thermal conductivity of LDPE/NiO composites measured by a \(\hbox {KD}_{{2}}\) prothermal analyser increases approximately two times for 40 wt.% of NiO loaded LDPE composites. This increase in the thermal conductivity of LDPE may be explained on the basis of a model based on particle size distribution. The coefficient of linear thermal expansion (CTE) of the samples has been measured by a thermo-mechanical analyser as a function of temperature. The experimental value of CTE is well explained by taking the inter-phase volume and interaction between the filler particles and matrix into account. The mechanical properties of LDPE/NiO composites show an improvement with NiO addition and are explained in the light of various models and correlations.

Effects of Flame Retardants Additives on the Properties of Low-Density Polyethylene

Low-density polyethylene (LDPE) has many unique properties such as lightweight and high chemical resistance. Unfortunately, it burns rapidly when it is exposed to a flame which limits its applications especially when flame resistance is to be considered. Different percentages of magnesium hydroxide and decabromide diphenyl ether (3.0, 5.0, 7.0, and 9.0 wt.%) were mixed with LDPE using a two-roll mill machine at 1600C for 2 minutes. Then, the tensile and flame retardancy tests samples were prepared by an injection molding process using an industrial plastic machine at 1600C. Flammability, rheological, tensile and thermal properties of the produced samples were tested using a flammability test apparatus, a melt flow index machine, a universal testing machine, and a differential scanning calorimeter, respectively. It was observed that the flame resistance of LDPE was improved with the addition of both flame retardants up to 7.0 wt.%, then it was reduced when 9.0 wt.% of flame retardants were used. This may be attributed to the poor mixing due to the increase in the polymer melt viscosity as observed from the melt flow index results. An increase in elastic modulus and a reduction in ductility of LDPE were observed with the increasing of flame-retardant contents while the ultimate tensile strength of LDPE was increased from 5.7 to 7.6 and 7.5 MPa when 9.0 wt.% and 7.0wt.% decabromide diphenyl ether and magnesium hydroxide were added. This is due to the fact that the additives act as a load carried and/or their effects on the degree of crystallinity of LDPE.

Preparation and Assessment of Phase Morphology, Rheological Properties, and Thermal Behavior of Low-Density Polyethylene/Polyhexene-1 Blends

ABSTRACTIn this work, polyhexene-1 (PH-1) is synthesized by polymerization of hexane-1 with Ziegler–Natta catalyst and melt blended with low-density polyethylene (LDPE). The phase morphology, rheology, crystallization, and thermal behavior of (LDPE)/PH-1 blends are investigated. A good compatibility is observed in the blends up to 10 wt% PH-1 and the most of the droplets in the fractured surface are covered with and buried in the LDPE matrix and at higher percentage the droplet particle size significantly increased. The effect of microstructure of the blends on the flow behavior is studied by small amplitude oscillation rheology. By decreasing the compatibility and increasing the particle size, the Cole–Cole plots are deviated from the semi-circular shape at higher percentages than 10 wt% of PH-1. The change in the crystallization and melting behavior of LDPE in the blends are studied by differential scanning calorimetry and X-ray diffraction (XRD). It is found that by increasing the PH-1 the melting temperature of LDPE decreased from 112.5 to 110.8°C and crystallization temperature increased from 95.2 to 97.7°C which is evident of the nucleation effect. The intensity of (110) peak in XRD test declined as a remake of amorphous part of LDPE and the degree of crystallinity of LDPE decreased from 28 to 22% at 20 wt% PH-1.

Plasma Treatment ofAgaveFiber Powder and Its Effect on the Mechanical and Thermal Properties of Composites Based on Polyethylene

Composites based on low-density polyethylene (LDPE) were prepared withAgavefiber powder (AFP) that was coated by plasma polymerization process using ethylene gas. Treated and pristine AFP were analyzed by infrared spectroscopy, scanning electron microscopy, and contact water angle for the assessment of surface properties. The polymer composites were prepared by melt mixing using 0, 5, 10, and 20 wt% of AFP and their mechanical and thermal properties were measured. Dispersion evaluation in water confirmed that the AFP treated changed from hydrophilic to hydrophobic behavior and it was also corroborated with water contact angle tests. The addition of treated and untreated AFP (200 mesh) at 20 wt% promotes an increase of Young’s modulus of the composites of up to 60% and 32%, respectively, in relation to the neat matrix. Also, an increase of crystallinity of LDPE was observed by the addition of treated and untreated AFP; however no significant effect on the crystallization temperature was observed in LDPE containing AFP.

Polymeric compounds materials with polyethylene ( LDPE) and fibers Maclura tinctoria tree ( Moraceae )

Costa Rica has extensive areas of tropical forests that, managed with care and knowledge, can provide renewable raw materials and conserve biodiversity. Here we characterize the branches, leaves and bark of the “Mora Tree”, Maclura tinctoria. We manufactured composite polymeric materials and applied infrared spectrometry, liquid chromatography, optical microscopy, and the analysis of thermal and mechanical properties. We found polyphenols in all parts of the tree. The natural substrate increases crystallization temperature and reduces the crystallinity of low density polyethylene (LDPE). The elasticity modulus is higher for the composite material than for the LDPE. The fibers of this species are a promissing alternative for new products and to reduce the environmental impact of traditional polymeric materials.

Effect of gamma irradiation on high temperature hardness of low-density polyethylene

Gamma irradiation can cause the change of microstructure and molecular structure of polymer, resulting in the change of mechanical properties of polymers. Using the hardness measurement, the effect of gamma irradiation on the high temperature hardness of low-density polyethylene (LDPE) was investigated. The gamma irradiation caused the increase in the melting point, the enthalpy of fusion, and the portion of crystallinity of LDPE. The Vickers hardness of the irradiated LDPE increases with increasing the irradiation dose, annealing temperature, and annealing time. The activation energy for the rate process controlling the reaction between defects linearly decreases with the irradiation dose. The process controlling the hardness evolution in LDPE is endothermic because LDPE is semi-crystalline.

Study of lignin dispersion in low-density polyethylene

A maximum of 20% (w/w) lignin was used as a filler in low-density polyethylene (LDPE), together with 3–6% maleic anhydride-grafted LDPE as compatibilizer and 3–10% copper(II) sulphate pentahydrate (CuSO4·5H2O) as lignin’s dispersing agent. The resulting composites were investigated for both their mechanical properties and their melting point following the ASTM standards as well as their behaviour was compared with neat LDPE. The results reveal that addition of compatibilizer significantly improved the mechanical properties of lignin, yielding closer values to those of neat LDPE. In fact, the addition of 3% maleated polyethylene induced a 37% increase of the Young’s modulus, whilst 3% CuSO4·5H2O provides a good lignin dispersion. The above observations are further supported by the scanning electron micrographs of the blend specimens. Finally, the differential scanning calorimetry analysis revealed that the melting temperature and the crystallinity of LDPE slightly increase with the addition of 3% CuSO4·5H2O.

Sulfonation of low-density polyethylene and its impact on polymer properties

Sulfonation of polymers is of great importance for the packaging industry mainly due to its effect on the alteration of surface functionality of polymer films. In this study we customized liquid phase sulfonation of low-density polyethylene (LDPE) swelling the polymer by using a combination of polar and nonpolar solvents. Swollen polymer was treated with sulfuric acid of varying concentrations with continuous mixing for in-depth sulfonation of the polymer. Presence of cyclohexane and ethanol, as polar and nonpolar reagents, not only kept the batch under isothermal conditions but also homogenously influenced in-depth functionalization of LDPE. The durability of the sulfonated polymer was determined by grinding the test samples 30 days after the reaction. Fourier transform-infrared spectroscopy indicated presence of functional group moieties, which is also supported by increase of 5% and 1.35% in density and sulfur contents of the polymer, respectively. Contact angle measurements indicate 30° decrease in values of the sulfonated polymer which corresponds with decrease in carbon to hydrogen ratio (from 5.9 to 5.3) and increase in sulfur to carbon ratio (up to 0.0184) resulting from the sulfonation of the polymer. Differential scanning calorimetery results indicate almost linear reduction in the crystallinity of LDPE with an increase in acid concentration used for the sulfonation reaction. POLYM. ENG. SCI., 54:2522–2530, 2014. © 2013 Society of Plastics Engineers

Preparation of low-density polyethylene/low-temperature expandable graphite composites with high thermal conductivity by an in situ expansion melt blending process

A facile strategy with the advantages of low cost and ease of mass production was presented to prepare low-density polyethylene (LDPE)/low-temperature expandable graphite (LTEG) composites with relatively high thermal conductivity by an in situ expansion melt blending process. LTEGs were expanded and delaminated into graphite multi-layers and graphite nanoplatelets during processing which synergistically created more thermo-conducting paths in the composites and hence led to great improvements in thermal conductivity. Thermal conductivity of the composite with 60wt% of LTEG loading was increased by 23 times as compared to the pure LDPE, increasing from 0.47 to 11.28W/mK. The incorporation of LTEG decreased the melting temperature and the degree of crystallinity of LDPE. Percolation threshold of both the electrical conductivity and rheological measurements was observed at about 8vol% of LTEG loading. Moreover, the LDPE/LTEG composites showed better thermal stability compared to the pure LDPE.

Thermal conductivity, coefficient of linear thermal expansion and mechanical properties of LDPE/Ni composites

Thermophysical and mechanical properties of low density polyethylene (LDPE) filled with nickel powder (10 μm) is reported. The composites are characterized by XRD, SEM, DSC and TGA. XRD analysis indicates that Ni affects the crystallinity of LDPE, whereas, scanning electron micrographs reveals formation of Ni clusters/conducting chains especially for high filler concentration. The DSC and TGA data show a marginal decrease in peak melting point and a moderate enhancement in thermal stability, respectively with increasing volume % of Ni in LDPE. Thermal conductivity of the composite increases by ~240 % with addition of 25 volume % of nickel and we confirm that the measured data is in excellent agreement with a percolation based model. Coefficient of thermal expansion (CTE) of LDPE decreases by ~38 % for composite with 25 volume % of Ni. The measured CTE agrees well with the estimates of a recent model which takes into account the interphase volume and interaction between filler particles and polymer. An overall improvement in mechanical properties is also observed for LDPE/Ni composites and the results are explained in the light of existing models.

Natural weather ageing of the low‐density polyethylene: Effect of polystarch N

AbstractBlends of low‐density polyethylene (LDPE) with Polystarch N were prepared by extrusion. Tensile properties, thermal behavior, and natural weathering of these blends were investigated as a function of blend composition. The addition of Polystarch N to the matrix decreased the tensile properties and the degree of crystallinity of LDPE when the proportion of Polystarch N increased in the blend, as revealed by differential scanning calorimetric studies. Scanning electron microscope analysis of the blends retrieved after being exposed to natural weathering showed that natural degradation increased with increase in the amount of Polystarch N in the LDPE and is ascribed to higher extent of chain scission as revealed by Fourier transform infrared spectroscopy analysis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Structural, luminescent and thermal properties of blue SrAl2O4:Eu2+, Dy3+ phosphor filled low-density polyethylene composites

Abstract The performance of nanophase luminophors is usually compromised by environmentally induced degradation. In this study, composites of low density polyethylene (LDPE) with various concentrations of the blue-emitting europium and dysprosium co-doped strontium aluminate (SrAl 2 O 4 :Eu 2+ ,Dy 3+ ) phosphor were investigated. The blue long-lasting phosphorescence of the composites was observed in the dark after removal of the excitation light. X-ray diffraction analysis revealed the presence of the SrAl 2 O 4 phase in the composites. PL spectra of the composites have two sets of peaks, major broad bands peaking at about 4855 A and minor ones at wavelengths between 4115 and 4175 A, attributed to the 4f–5d transition of Eu 2+ . DSC and TGA results show that the introduction of the phosphor in LDPE matrix caused a slight reduction in the crystallinity of LDPE but a significant increase in the stability of the composites.

Preparation and characterization of low‐density polyethylene/banana starch films containing compatibilizer and photosensitizer

AbstractComposite films containing various percentages of banana starch and low‐density polyethylene (LDPE) were prepared. The effects of the compatibilizer, banana starch content, and photosensitizer content on the thermal and tensile properties of these films were investigated. The banana starch content was varied from 5 to 20 wt % of LDPE, whereas benzophenone was added as a photosensitizer in three different amounts (0.25, 0.5, and 1 wt %) based on LDPE. In these films PE‐graft‐maleic anhydride (PE‐g‐MA) was used as a compatibilizer at 10 wt % banana starch. It was found that the thermal stability of the composite films remained unchanged with respect to the amount of banana starch and benzophenone content. The addition of banana starch had no effect on the melting temperature and degree of crystallinity of the films. Similarly, PE‐g‐MA had no effect on the melting temperature but decreased the degree of crystallinity of the LDPE phase. Benzophenone caused an increase in the melting temperature but decreased the degree of crystallinity of LDPE in the films. Increasing the amount of banana starch decreased the tensile properties of the composite films. The addition of PE‐g‐MA as a compatibilizer increased the tensile properties compared with the uncompatibilized films. However, benzophenone had no effect on the tensile properties of the blend films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2717–2724, 2006

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

AbstractThe 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