High Density Polypropylene Research Articles

Effect of the Percolation of NR on Mechanical Properties of HDPE/PP/NR Blends

The effect of the connectivity of an elastomer in a blend of two polyolefins was studied. Blends of natural rubber (NR) with high density polyethylene (HDPE) and polypropylene (PP) were prepared using a Banbury mixer at 180°C. The samples were laminated by compression molding at 180°C and quenched in water at room temperature. Extraction of the natural rubber was performed for blends containing equal relative amounts of both polyolefins. The percolation of the rubber within the matrix of both polyolefins started to occur at about 20% rubber content. Mechanical properties, such as Young's modulus and stress at break, showed the effect of the percolation phenomenon.

Characterization by thermal analysis of high density polyethylene/polypropylene blends with enhanced biodegradability

Blends of high density polyethylene (HDPE) and polypropylene (PP) with different biodegradable additives have been subjected to an outdoor soil burial test. The effect of the degradation process on the structural and morphological properties of the samples has been studied by thermogravimetry, differential scanning calorimetry, and dynamic-mechanical spectroscopy. The thermogravimetric results show that the additive is more affected by the degradation process than the polymeric matrix. Changes both in the crystalline morphology and the activation energies of the relaxation processes take place in different stages, and can be described using polynomial equations. These changes occur on different time scales depending on the additive used. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 174–185, 2002

Effects of gamma irradiation on polypropylene, polypropylene + high density polyethylene and polypropylene + high density polyethylene + wood flour

The effect of the gamma-irradiation on the mechanical properties of the composites, Polypropylene (PP), PP+high density Polyethylene (HDPE), PP+ HDPE+wood flour, where HDPE is virgin and recycled, was studied. This paper discusses the behavior of the composites after exposure to various doses of gamma irradiation (1–7 MRads) in the presence of oxygen. The dependence of mechanical properties on the integral dose for a constant dose rate of 0.48 MRads/h confirms the influence of the irradiation. Strong effects on the elongation at break and break strength is noticed. The mathematical analysis suggests for the PP+r-HDPE a bimolecular process of the elongation at break. On the order hand, for the PP+HDPE a complex process is represented for a three exponential equation.

Foams Made from Blends of Ethylene Styrene Interpolymers with Polyethylene, Polypropylene and Polystyrene

INSITE** Technology from The Dow Chemical Company has enabled the production of ethylene-styrene Interpolymers (ESI) by copolymerization of ethylene and styrene monomers. The properties of interpolymers vary significantly with copolymer styrene content. Interpolymers with up to about 45 weight percent copolymer styrene are semicrystalline and exhibit good low temperature toughness. Interpolymers with greater than about 45 weight percent copolymer styrene are essentially amorphous and range from those that have low modulus and high elongation to those that have higher modulus with unique stress relaxation and dead fold properties. Interpolymers have both aromatic and aliphatic functionality. Hence, they are compatible with a variety of other thermoplastics. Interpolymers have been commercially launched under the trademark "INDEXt Interpolymers" and are classified as E-Series (up to about 45 weight percent styrene) or S-series (greater than about 45 weight percent styrene). This paper describes the properties of blends of interpolymers with low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), as well as the novel and unique foams made by expanding some of these blends with physical blowing agents.

Moisture sorption isotherms of nutritious supplementary foods prepared from cereals and legumes for feeding rural mothers and children

Four types of supplementary foods (FSs) based on popped wheat (Triticum vulgare), ragi (Eleusine coracana), bajra (Pennisetum americanum) and sorghum (Sorghum bicolor) blended with soy (Glycine max Merr) and bengalgram (Cicer arietinum) and fortified with vitamins and minerals were prepared on a pilot plant scale. All the FSs contained 10–20% proteins and 350–380 kcal of energy. Moisture sorption characteristics of these FSs were evaluated at room temperature (27 °C) with a view to designing a functional package for such products. The results revealed that a moisture content of about 10% (equilibrium relative humidity 68–70%) is optimum to give a good storage stability to the products. Above the 10% moisture level the products were found to be vulnerable to microbial spoilage (mould growth), leading to quality deterioration. In order to protect these types of products from being spoiled by mould growth during storage, use of moisture-proof packaging materials based on high density polyethylene and polypropylene may be considered.

Equal channel angular extrusion of polyalkenes

The deformation of both high density polyethylene and polypropylene undergoing equal channel angular extrusion (ECAE) has been investigated, and the resultant molecular orientation characterised by X-ray diffraction. The ECAE process using a 45° extrusion angle is found to result in permanent deformation only when a considerable backpressure is applied, whereas 90°extrusion results in plastic strain without backpressure, albeit requiring lubrication. The extent of the shear strain acquired is generally less than the theoretical maximum, indicating that elastic bending plays a significant role in the angular extrusion of these polymers. The crystalline orientation is found to be similar to the orientation caused by simple shear, where two different preferred molecular orientations are found, and which can be attributed to two different slip systems operating. In addition, a partial change in crystalline form is observed, with the appearance of a monoclinic crystalline fraction after deformation.

Thermal and photostabilization behaviour of a novel naphthalene-HALS derivative in HDPE and PP films

A novel N-[-8-(2-naphthoxy)Octyl]-4-amino,2,2,6,6-tetramethylpiperidine stabiliser has been synthesised and characterised and its thermal and photostabilising performance examined in both high density polyethylene and polypropylene films. Its performance has been compared with that of a commercial hindered piperidine light stabiliser, Tinuvin 770 together with the effects of naphthalene. Using FTIR analysis, the naphthoxy-HALS showed excellent properties as a thermal and photostabiliser, showing strong autosynergism in the former case. Comparisons with Tinuvin 770, showed that the naphthalenic moiety of the molecule plays a role in the thermal stabilization process by scavenging oxygen. Naphthalene itself exhibited some degree of thermal stabilization and reversed its behaviour from being a weak stabilizer at low concentrations to a prooxidant at higher concentrations. The same pattern of stabilization was observed during the photoaging of polypropylene with the exception of the mixture of Tinuvin 770 and naphthalene which was found to exhibit the best performance at the higher concentration.

Thermal and photo-oxidative stabilisation of polyolefin films: mode of action of novel naphthalene-hindered piperidine derivatives

Four novel naphthyl and naphthoate derivatives of tetramethyl and pentamethylpiperidine (HALS) have been synthesised, characterised and evaluated as thermal and light stabilisers in both high density polyethylene (HDPE) and polypropylene (PP) film using FTIR analysis. The naphthalene moiety is found to induce good dual thermal and light stabilising activity in the polymers. In terms of thermal oxidative stability, the secondary HALS were better than the tertiary HALS systems and vice-versa for photostabilisation. From mass spectrometric evidence and photochemical studies the naphthalene and naphthyl moieties sever rapidly during the early stages of degradation, resulting in effective oxygen scavenging products protecting the HALS moiety from oxidation.

Surface modification of high density polyethylene and polypropylene by DC glow discharge and adhesive bonding to steel

Abstraet-The surface modification of high density polyethylene (HDPE) and polypropylene (PP) has been carried out by exposure to a DC glow discharge in air at different power levels of 5.28, 11, and 13 W. The surface energies of polymers exposed to glow discharge were estimated by measuring the contact angles of two test liquids: de-ionized water and formamide, whose surface energy components are known. Both the polar and the dispersion components of the surface energy increased rapidly at short exposure times but the increase of the polar component was relatively more than that of the dispersion component. At low power levels of 5.28 and 11 W, the polar component of the surface energy reached a maximum plateau depending on the exposure time, but at a 13 W power level the polar component of the surface energy decreased from a maximum value to a saturation level. For PP, this saturation level could not be attained in this study. The maximum total surface energy measured in this study corresponds to the maximum polar component at 13 W for an exposure time of 120 s. The contact angle of the adhesive, Araldite AY 105 mixed with hardener HY 840 in a weight ratio of 2 : 1, was minimum at this maximum surface energy attained with HDPE and PP by exposure to a glow discharge in air. The measured lap shear strengths of HDPE or PP-Araldite-mild steel joints show a maximum corresponding to the maximum surface energy measured on the above-mentioned polymers.

High frequency electrical measurements of adhesive bonded structures — An investigation of model parallel plate waveguide structures

Analysis using a network analyser of the electrical response between 300 kHz and 200 MHz for a range of model waveguide structures is discussed. The structures chosen illustrate the variations to be expected in real adhesive bonds and include changes in bond line thickness, width and electrical conductivity of the substrate. A simple theoretical model was used to simulate the time domain data and very good agreement between experiment and theory was observed. Deficiencies in the model appeared when it was used to simulate frequency domain data, and the limitations of these calculations are critically discussed. The accuracy to which this method can be used to calculate the dielectric permittivity was assessed from a study of a number of polymers with well-defined dielectric characteristics. Parallel plate structures were fabricated using low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polycarbonate (PC) and polymethyl methacrylate (PMMA). Good agreement between literature and experiment was observed in all cases, validating the dielectric permittivity values obtained using this approach. This paper illustrates the potential of nondestructive electrical measurements to provide structural and quantitative permittivity information on adhesive joint structures.

Molecular Orientation Behavior with Drawing of Biaxially Stretched Film

Biaxially stretched poly (ethylene terephthalate) (PET), isotactic polypropylene (PE) and isotactic high density poly-propylene (HCPP) films have been characterized by crystallinity, dielectric constant, refractive index and birefringence. Anisotropy of refractive index by microwave for PET, PP and HCPP biaxially stretched films indicated higher value than refractive index by Abbe refractometer. We recognized good correlation between refractive indices by microwave and Abbe refractometer for biaxially stretched PET, PP and HCPP films, respectively.

Morphology and Rheological Properties of PE/PP Blend Fibers

Abstract Blends of high density polyethylene (HDPE) and polypropylene (PP) were prepared by the melt mixing method. The morphology and the rheological properties of extrudates were measured and related with the physical properties of the melt spun fibers, such as X-ray diffraction patterns, tensile properties, and birefringence. From the SEM photographs of the fractured surfaces, it can be seen that PP forms a continuous phase in blends of 25% and 50% of HDPE, while HDPE formed in a 75% blend. In all cases, the discrete phases were finely distributed. The viscosity and the melt elasticity of HDPE were higher than those of PP and those of HDPE/PP blends were intermediate. The first normal stress difference of the extrudates increased with the increase of HDPE content, and thus the birefingence and the initial modulus of the spun fibers did with the HDPE content. However, the crystalline orientation did not show any dependence on the composition. Tenacity showed a deviation from linearity due to the incompa...

Flow History – Morphology Development in Crystallizable Polymer Melts

Abstract Flow history-morphology interactions have been studied for three crystallizable polymers: high density polyethylene, poly(vinylidene fluoride), and polypropylene. Materials were extruded through an impinging channels film die which produces a mixed extensional and shearing flow field. Extrudate morphology was characterized by optical microscopy and x-ray diffraction. Stress fields during die flow were measured from flow birefringence and compared to calculations based on the power law model. Good quantitative agreement was found for the shearing stresses, however, large differences were observed between the measured and computed normal stresses along the symmetry axis of the flow where extensional gradients are also the highest. Extensional stresses on the order of 2.8·106, 1.4·106, and 3.9·105 dynes/cm2 were required to induce row-nucleated crystallization in the HDPE, PVF2, and polypropylene respectively. The respective stresses were found to decrease with increasing relaxation time in a non-linear fashion. An explanation for this behavior is presented based on the opposing tendencies of chain relaxation and oriented crystallization.

Reactions occurring in the induction period of inhibited oxidation of polypropylene

A study has been made of O 2 absorption during the induction period for high density polypropylene (HDPE) in the interval 200–230°C, using N-phenyl- N′-cyclohexyl- p-phenylediamine as a strong anti-oxidant. The rate of O 2 absorption at 210°C in the presence of the antioxidant changes during the induction period from 2 × 10 −6−2 × 10 −5 mol/kg s. The main direction of antioxidant consumption during the induction period is direct oxidation by O 2. Rapid oxidation of the PE starts if the current concentration of the antioxidant falls below a certain critical level. The kinetic parameters have been determined for the oxidation reaction using a wide range of initial concentrations of the antioxidant.

An approach to the estimation of polymer melt elasticity

An effective method has been proposed to estimate the primary normalstress difference versus shear rate curves at temperatures relevant to the processing conditions only from the knowledge of the melt flow index, the molecular-weight distribution and the glass transition temperature of the polymer. The method involves the use of a unified curve obtained by coalescing the elastic response curves of various grades in terms of the modified normal-stress coefficientψ1 ⋅ (MFI)2 and a modified shear rate\((\bar M_z /\bar M_w )^{3.5} (\dot \gamma /MFI)^2 \). Unified curves have been reported for low density polyethylene, high density polyethylene, polypropylene and nylon.

A review of dielectrics for flexible superconducting cables

Abstract The tape materials for the dielectric of a flexible superconducting cable are discussed. The tape is wrapped around the superconductor and is impregnated with supercritical helium. Based on mechanical and electrical performance the most promising materials are Valeron, high density polyethylene, polypropylene, and nylon 11. A final assessment is made based on life expectancy and mechanism of electrical failure both of which are a function of discharge activity in the tapes.

A SIMPLIFIED APPROACH TO THE PREDICTION OF PRIMARY NORMAL STRESS DIFFERENCES IN POLYMER MELTS

Abstract A relationship between the unified primary normal stress difference function and the unified viscosity function curves proposed earlier by the authors is sought based on a strain dependent single integral constitutive equation of the BKZ-type. The predictions of the equation are checked for best fit of the unified primary normal stress difference curves of low density polyethylene, high density polyethylene, polypropylene and nylon. The approach is then extended to give theoretical predictions of the unified primary normal stress difference curves for a number of other polymers whose unified viscosity curves are known. The approach provides a method to estimate the normal stress difference versus shear rate curves at any temperature through the unified curves merely from the knowledge of the melt flow index.

Polymerization of Butadiene Using Ziegler-Natta Catalysts—Recent Developments

Abstract The products of Ziegler-Natta catalyzed reactions, including high density polyethylene, polypropylene, and other thermoplastics and elastomers, have become familiar to all. While an enormous volume of experimental work was completed during the 1950s and 1960s, it has only been during the 1970s that the multiplicity of mechanistic schemes developed have been subjected to scrutiny. The majority of these have been concerned with polymerization of ethylene and α-olefins and because they have been adequately reviewed recently, are discussed only briefly here. A similarly large volume of empirical experimental work has enabled commercial production of polybutadiene using stereoregular catalysts. However, the mechanisms involved are of recent development, largely due to the additional configurational complexity of products, the multicompound nature of the catalyst complex, and the susceptibility of the system to contamination. Advances which have been made during the last decade are highlighted, with pa...

Extrusion coating and its applications

Extrusion coating and laminating developed during the 1940s in the United States and was introduced to the United Kingdom on a commercial scale about a decade later. By the use of extrusion coating it is possible to combine the desired properties of the substrate and of the coating medium. Common substrates are paper, board, tissue, fabric, film and foil and the vast majority of coating and laminating media are polymeric plastics of which low density polyethylene is the one most often used. However, medium and high density polyethylene, polypropylene and other less common polymers are becoming increasingly used. By the judicious choice of the substrate, coating medium and machine conditions it is possible to develop packaging materials and other membranes with whatever combination of properties are required—barrier properties against moisture greases or gases, appearance, handle etc. Perhaps the most important basic properties when considering any particular polymer for extrusion are Melt Index and Density and the machine variables most likely to affect the final product are melt temperature, die-nip distance and nip roll pressure. Common uses for extrusion coated and laminated products are outlined showing how the materials are used for packaging and to provide membranes generally throughout industry from consumer packaging through to the building trade. Special mention is made regarding how extrusion can save resources and hence money for the user.

Rheological properties of polystyrene melts

Measurements were taken of both viscous and elastic properties of polystyrene melts, using a capillary rheometer recently constructed byHan. The viscous property is determined from the slope of the axial pressure distribution, and the elastic property is determined from the exit pressure, which is obtained at the tube exit when the straight line portion of the axial pressure profile is extrapolated to the exit of the tube. Previous studies ofHan demonstrated that the exit pressure thus obtained can be correlated with die swell ratios, and that the exit pressure is equal to the normal stress difference for polymer melts in fully developed viscometric flow. The present study of polystyrene melts corroborates all previous correlations obtained with high density polyethylene and polypropylene melts as regard the exit pressure measurements. A salient feature of the method employed here is that it requires only a single capillary, long enough to assure that flow is fully developed.