Studies on LDPE/LLDPE blends

The kinetics of crosslinking reaction of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) using dicumyl peroxide (DCP) as the initiator and tetrakis [methylene 3-(3’,5’-di-t-butyl-4’-hydroxyl)propanoate] (Irganox 1010) as the inhibitor were studied using Brabender Plasti-Corder (BPC) and Differential Scaning Calorimeter (DSC). The crosslinking reaction in the absence of inhibitor was found to be first order with respect to initiator concentration, while in the presence of inhibitor, the reaction was first order with respect to initiator concentration and 0.21-0.31 with respect to inhibitor concentration at 446 K for BPC and 413 K for DSC. In addition, the rate constant in the presence of inhibitor was found to be around three time lower than that in the absence. The activation energy of crosslinking reaction of LDPE and LLDPE were 118 and 112 kJ/mol, respectively for BPC technique and 184 and 176 kJ/mol, respectively for DSC technique. The pre-exponential factor of crosslinking reaction of LDPE and LLDPE were respectively 3.23 x 10¹¹ and 0.82 x 10¹¹ sec⁻¹ for BPC technique and 3.56 x 10¹⁹ and 3.64 x 10¹⁸ sec⁻¹ for DSC technique. The fraction of termination was determined and found that approximately 65% was terminated by combination of polymer radicals, while 35% was terminated by disproportionation and cyclization. The amount of DCP higher than 1.6%w/w used for the crosslinking reaction gave the degree of crosslinking in polymer greater than 80%. When 0.1-0.2%w/w of Irganox 1010 was used in the preparation of compound LDPE or LLDPE containing about 2%w/w DCP, the degree of crosslinking was constant at more than 80%. For the Iragox 1010 concentration greater than 0.2%w/w, the degree of crosslinking decreased with increasing inhibitor concentration.

Poly (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.

Crosslinking of polyethylene would improve and modify its properties. A preferred method of crosslinking is via its silane grafting, initiated by peroxide. In this study, the grafting reactions of different types of low density (LDPE), linear low density (LLDPE) and high density polyethylene (HDPE) were studied and compared in efficiency, all in a fixed amount of silane (vinyltrimethoxysilane) and peroxide (dicumyl peroxide). Processing for silane grafting was carried out in an internal mixer for 15 minutes at 190 oC, and the silane grafting efficiency was determined through the corresponding peaks in their FTIR spectra. The effect of polymer physical form (powder versus granule) and premixing (the polymer with silane-DCP solution) prior to processing was also determined. In case of LDPE and LLDPE, three types of antioxidants (Irganox 1010, Irganox 1076, and KV10) were incorporated into the reaction mixture to assess their probable interference and effectiveness in grafting reaction. Finally, LDPE was melt blended with ethylene vinyl acetate (EVA) and once again with ethylene propylene diene monomer (EPDM) to investigate their effect on silane grafting efficiency. Amongst different grades of polyethylene, LLDPE had a better efficiency in silane grafting with regard to LDPE and HDPE. Furthermore, the lower molecular weight of polyethylene with narrower molecular weight distribution resulted in the more efficient silane grafting. In case of incorporating antioxidant, Irganox 1010 followed by Irganox 1076 had the best performance for LDPE, however, KV10 turned out to be more suitable for LLDPE. Finally, higher silane grafting efficiency was gained through blending polyethylene with EVA and EPDM.

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.

The mechanical, optical and electrical properties of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) films with and without fillers have been studied. The variation of properties resulting from the addition of inorganic fillers included an increase in haze, diffusion of light, and tear strength for films made with both LDPE and LLDPE, while increasing the burst strength and elongation of the LDPE films only. The tensile strength, melt flow rate, and usually the seal strength were decreased with the addition of fillers. The coefficient of friction (COF) was decreased when silica or commercial grade mica were added to both LDPE and LLDPE films.

Oriented structure and anisotropy properties of polymer blown films: HDPE, LLDPE and LDPE

Through this paper an experimental investigation has been done. The composites of different reinforced material having significantly good strength and improved properties are prepared. A comparative study was performed among LLDPE with non-woven fabric, LLDPE and non-woven fabric reinforced with rice husk, LLDPE with non- woven fabric and ash of rice husk. Linear Low Density Polymer (LLDPE) is used as base material in this fabrication process. LLDPE is mixed with the non-woven fabric in different percentage composition by weight in addition to the other natural reinforcement material (rice husk). Further an experiment was performed to calculate the mechanical properties like tensile strength, Melt flow Index (MFI), flexural strength, hence a comparative study of composite with different types of reinforcement was done to investigate the effect of mixing of different reinforcement material. Results shows that LLDPE with non-woven fabric (15 %) have less strength as compared to LLDPE with non-woven fabric and rice husk (10 %) and LLDPE with non-woven fabric and ash of rice husk (5 %). Water absorption characteristics are studied following ASTMD 570, results shows that LLDPE absorbs 0.15 per cent water, followed by LLDPE with rice husk (0.03 %) and LLDPE with ash (0.038 %).

Packaging is the subject of considerable commercial development by a variety of organizations around the world. In this study the mechanical, thermal and rheological properties were investigated for different blend ratios of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). The weight percent of the LDPEs used in the blends were 50, 60, 70, 80 and 90. The polymer blends were prepared in a twin screw extruder to produce a thin sheet (1-mm thickness) similar to the packaging grade. Tensile results showed that the 50/50 composition exhibited the highest stress at break, where the differential scanning calorimetry results indicated a co-crystalline phase in some blends. The results produced by the rheometer revealed the LLDPE effect over the complex viscosity and consequently blend easy processing. The present study conclusively demonstrates that at low weight percent of linear low density polyethylene in the blend displays better properties for packaging application.

Thermal characterisation of LDPE and LLDPE blends

Melt blending of linear low density polyethylene (LLDPE) and polylactide (PLLA) was performed in an extrusion mixer with post extrusion blown film attachment with and without compatibilizer-grafted low density polyethylene maleic anhydride. The blend compositions were optimized for tensile properties as per ASTM D 882-91. Based on this, LLDPE 80 (80 wt% LLDPE & 20 wt% PLLA) and M-g-L 80/4 (80 wt% LLDPE, 20 wt% PLLA and 4 parts compatibilizer per hundred parts of resin) were found to be an optimum composition. FTIR reveals that the presence of compatibilizer shifts carbonyl peak hence some increase in interaction between LLDPE and PLLA. Morphological characteristics of the fracture surface of with and without compatibilizer blends were examined by scanning electron microscopy. It shows that use of compatibilizer enhances the dispersions of PLLA in LLDPE matrix. Thermogravimetric (TG) analysis of blends shows the M-g-L 80/4 blend has higher thermal stability among studied blends. The degradation study under different pH of soil compost gives that in alkaline condition and the presence of compatibilizer was favorable for degradation. This blend may be used for packaging application.

Studies on melt flow properties of low density and linear low density polyethylene blends in capillary extrusion

The aim of the present study is to investigate in detail the near infrared (NIR) spectra of the three types of polyethylene, linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE), and to develop calibration models that predict their physical properties such as density, crystallinity and melting point. The effects of spectral resolution on the classification and the prediction of density for the three types of PE have been investigated. Furthermore, the NIR spectral differences among LLDPE, LDPE and HDPE have been explored in more detail using 2 cm−1 resolution. Principal component analysis (PCA) has been performed to differentiate the 18 samples of PE. They are classified into three groups, LLDPE, LDPE and HDPE, by a score plot of the PCA Factor 1 versus 3 based on the NIR spectra pretreated by multiplicative scatter correction (MSC). The 2 cm−1 spectral resolution yields a slightly better result for the classification. Partial least squares (PLS) regression has been applied to the NIR spectra after MSC to propose calibration models that predict the density, crystallinity and melting point of HDPE, LDPE and LLDPE. The correlation coefficient for the density was calculated to be 0.9898, 0.9928, 0.9925 and 0.9872 for the spectra obtained at 2, 4, 8 and 16 cm−1 resolutions, respectively, and the root mean square error of cross validation ( RMSECV) was found to be 0.0021, 0.0018, 0.0018 and 0.0023 g cm−3, respectively. It has been found that the correlation coefficient and RMSECV for the prediction of the density and crystallinity change little with the spectral resolution. However, for the prediction of melting point, the higher resolutions (2 and 4 cm−1 resolution) provide slightly better results than the lower resolutions. NIR transmission spectra of thin films of LLDPE, LDPE and HDPE have also been investigated, and calibration models for predicting their density have been developed for the film spectra.

A direct method for evaluating polymer foamability

A two-step isothermal annealing (TSIA) procedure is described that enables the endothermic peaks of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and their blends, to be satisfactorily resolved during analysis by differential scanning calorimetry. A modified form of multistep isothermal annealing, the TSIA procedure produces a highly characteristic profile of the blend components by facilitating the segregation of the phases based on branch density. It is proposed that the TSIA procedure may have significant merit in the identification and quantification of the components in an unknown blend as well as increasing the sensitivity in analytical procedures aimed at blend component quantification.

A Monte Carlo (MC) simulation is performed on peroxide induced branching reactions in a linear low density polyethylene (LLDPE) melt processed with different dicumyl peroxide (DCP) concentrations at various processing times and temperatures. The MC simulation can successfully monitor the microstructural changes due to the induced long chain branching (LCB), decreased terminal double bonds, and increased trans vinyl bonds in LLDPE during peroxide modification. The induced structural changes are in good agreement with the experimental results obtained by rheometery and SEC analysis. The changes in the gel content, , and MWD as a result of the peroxide modification are also determined. The simulation results also reveal that the chemical mechanism by which the modification proceeded is closely related to the changes in concentrations of reactive vinyl species of the PE molecules. Moreover, the results indicate that the degree of induced LCB increases almost linearly with the DCP concentrations. The findings of this paper indicate that the MC simulation method is able to predict the suitable processing conditions needed for inducing desirable structural changes in a LLDPE.