Neat Low-density Polyethylene Research Articles

Melt rheology and extrudate swell of low-density polyethylene/ethylene–octene copolymer blends

The melt rheological and extrudate swelling behavior of neat low-density polyethylene (LDPE) and blends of LDPE and ethylene–octene copolymer (EOC) was investigated using capillary rheometry at 185.0±0.5 °C. Dies having different length-to-inner diameter ( L/D) ratios were used (i.e., 5/1, 10/11, 10/2, and 30/2 mm/mm, respectively). For a given sample material, the real shear stress was observed to increase with increasing real shear rate, and, for a given real shear rate, the real shear stress was generally observed to increase with the addition and increasing amount of EOC. All of the sample materials exhibited the shear-thinning behavior. Both the tensile stress and the elongational viscosity were found to decrease with increasing elongational rate. Generally, both the tensile stress and the elongational viscosity increased with the addtion and increasing amount of EOC, with an exception for the 85/15 and 80/20 LDPE/EOC blends which exhibited a reversed order. Lastly, the extent of extrudate swelling of the sample materials in the small dies (i.e., inner diameter=1 mm) was greater than that in the larger ones (i.e., inner diameter=2 mm) and the use of a longer die also helped suppress the extent of the extrudate swelling.

Effect of cobalt carboxylates on the photo-oxidative degradation of low-density polyethylene. Part-I

The effect of three cobalt carboxylates of increasing chain length, namely cobalt laurate, cobalt palmitate and cobalt stearate on the photo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. LDPE films containing cobalt carboxylates were irradiated with UV-B light at 30 °C for extended time periods. FTIR spectroscopy, mechanical testing, morphological studies, molecular weight, density and MFI measurements were performed to monitor the degradation behaviour. The results of these studies were analysed to explain the structural and chemical modifications taking place in the polyethylene matrix due to UV-B exposure. FTIR studies indicate that the degradation is dominated by formation of carbonyl and vinyl species. The studies on mechanical properties reveal that samples containing cobalt carboxylates, become mechanically fragile after UV exposure for 400 h, while neat LDPE exhibits insignificant changes during this period. The degradation was found to increase proportionally with increasing chain length and follows the order CoSt 3 > CoPal 3 > CoLau 3. Migration studies were performed on food simulant systems to investigate the applicability of these films for food packaging.

Effects of Compositions and Processing Variables on Barrier and Mechanical Properties of Liquid Crystalline Polymer/Polyethylene Blend Films

AbstractCast films of liquid crystalline polymer (LCP) and low density polyethylene (LDPE) blends have been produced and investigated. Effects of LCP content and processing parameters, i.e., processing temperature profile, screw speed, and post‐die drawing, on morphology and O2 barrier property are presented. Increasing processing temperature and LCP content tend to enhance aspect ratios (L/D) of the LCP dispersed phase and at the same time influencing LCP structure. These effects are clearly observed when LCP content is increased from 10 % to 30 % by wt. At high temperature profiles, LCP morphologies are presented in a more or less ‘ribbon’ or ‘tape’ like structure together with a common LCP fibrillar structure. Films of 10% and 30% LCP produced at two optimum temperature profiles show a noticeable proportion of LCP tape‐like structure and interestingly high barrier properties of ∼1.6 and 5.5 times that of the neat LDPE films. High barrier characteristics of such LCP/PE blend films are indicated by low oxygen transmission rate values. Apart from processing temperature effect, increases of screw speed result in films having smaller aspect ratios for both LCP fibers and ribbons; films also exhibit poorer barrier and mechanical properties. However, post‐die drawing clearly demonstrates a positive effect in improving aspect ratios of the LCP domains and the resulting films' moduli. Effects of post‐die drawing on enhancing films' barrier properties become more pronounced at high LCP content. By comparing with the neat LDPE film (30 μm thick) having modulus of ∼180 MPa and OTR of ∼11000 cc/m2.day, the developed LCP/PE films containing 30 wt% LCP show remarkably high modulus values of ∼1100 MPa with low OTR of ∼2000 cc/m2.day.

Influence of Nanoparticle Surfaces on the Electrical Breakdown Strength of Nanoparticle-Filled Low-Density Polyethylene

The electrical breakdown strength of TiO2nanoparticle-filled low-density polyethylene (LDPE) nanocomposites was investigated. It was found that the surface water on the nanoparticles played a very important role in determining the breakdown strength. The breakdown strength at 63.2% cumulative failure probability (E0) for the composites filled with dried nanoscale TiO2was similar to that of neat LDPE and 50% higher than that for the samples filled with as-received nanoscale TiO2. This increase was due to a better dispersion, a better interface, and a morphology change of the matrix. It was also found that surface modification of nanoscale TiO2had a significant influence on the breakdown strength.N-(2-aminoethyl) 3-aminopropyl-trimethoxysilane (AEAPS)-coated TiO2-filled samples showed about 40% higherE0than that of uncoated, as-received TiO2-filled samples. This was mainly due to enhanced electron scattering because of the presence of polar groups in AEAPS.

Thermogravimetric analysis of compatibilized blends of low density polyethylene and poly(dimethyl siloxane) rubber

The thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis of compatibilized blends of low density polyethylene (LDPE) and poly(dimethyl siloxane) rubber (PDMS) in the proportion of 50:50 containing different proportions of ethylene methyl acrylate co-polymer (EMA) as compatibilizer have been studied. EMA acts as a chemical polymeric compatibilizer for the binary blend system of LDPE and PDMS, the proportion of which varied from 0 to 15 wt.%. The TG and DTG of the blends show that the thermal degradation takes place in two stages, where as neat LDPE shows a three stage degradation and neat EMA and PDMS show only single stage degradations respectively. The activation energies at 10% degradation have been determined using Freeman and Carroll's method and found to be maximum (171 kJ/mol) for the blend containing 6 wt.% of EMA. Half life periods at 200 °C have been evaluated by the Flynn and Wall method and found to be maximum for the blend containing 6 wt.% of EMA.

Use of poly(ethylene‐co‐vinyl alcohol) as compatibilizer in LDPE/thermoplastic tapioca starch blends

AbstractPoly(ethylene‐co‐vinyl alcohol) (EVOH) was used as a compatibilizer to make blends of low‐density polyethylene (LDPE) and plasticized starch (TS). The tensile properties and impact strength were measured and compared with those of neat LDPE. The morphology of the blend specimens, both fractured and unfractured, was observed by scanning electron microscopy. Comparison of the properties showed that the impact strength of the blend improves significantly by the addition of a compatibilizer even with a high TS loading of 40 and 50% (by weight). A high elongation at break almost matching that of neat polyethylene was also obtained. The blend morphology of the etched specimens revealed fine dispersion of the starch in the polyethylene matrix, while the fracture surface morphology clearly indicate that the failure of compatibilized blends occurs mainly by the ductile mode. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3126–3134, 2002

Dynamic two-dimensional infra-red spectroscopy of the crystal—amorphous interphase region in low-density polyethylene

Dynamic two-dimensional Fourier transform infra-red ( FT i.r.) spectroscopy has been used to study the nature of the interphase in low-density polyethylene (LDPE). A two-dimensional correlation analysis on the dynamic spectra indicates that neat LDPE is comprised of three regions: an ordered crystalline region, a disordered, liquid-like region, and a crystal/amorphous interfacial region. The 1468 cm −1 peak in the methylene bending region is assigned to all- trans structures which primarily reside in the interfacial region. A variety of LDPE samples with different additives are used in order to determine how the additives influence the dynamic mechanical properties of each morphological phase. It is found that talc associates with the crystallites, ethylene vinyl acetate is distributed in all three morphological phases of the LDPE, and pyrene is associated only with the non-crystalline regions.