Polyethylene (PE), despite having the simplest basic structure of any polymer (a repetition of CH2 units), is the largest tonnage plastics material. The main attractive features of PE are its low price, excellent electrical insulation over a wide range of frequencies, very good chemical resistance, good processability, toughness, flexibility, and—in thin films of certain grades—transparency. Until the mid-1950s, all commercial PE was produced by high-pressure processes: these processes result in branched materials of moderate number average molar mass, Mw < 50 kg mol−1, classified as low-density PE. The discovery that some metal compounds, based on Cr (Phillips catalyst) or Ti (Ziegler–Natta), are able to catalyze the polymerization of ethylene in less extreme conditions has allowed the controlled synthesis of a large varieties of PE architectures with very diverse properties. PE grades ranging from high-density to linear low-density, as well as ultra-high molar mass and other PE copolymers of commercial significance are discussed in this chapter.

Chapter 10 – Polyethylene

The importance of surface roughness with respect to the bulk properties of dielectric materials is often overlooked. Surface roughness or interfaces between different material layers often significantly affects the external properties of thin films. Surface roughness holds its commonalty and critical impact among many materials properties. This review summarises the recent work on the effect of surface roughness on the mechanical, thermal, physical, and dielectric properties of dielectric films. Appropriate roughness favours adhesion, filtration, biological fouling, tribological properties, and magnetic properties. Nevertheless, lower roughness generally benefits the dielectric properties of dielectric materials, with thicknesses ranging from a few nanometres to up to 50 μm. This review discusses surface roughness control and the techniques of measurement as well. It emphasises the importance and characterisation of sample surface roughness for a better understanding of the dielectric phenomenon, mechanisms, and electrical stress test setup for various dielectric films.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/nde2.12026

A review of surface roughness impact on dielectric film properties

UV-absorbing nanoparticles (NPs) and microparticles (MPs) were prepared by emulsion and dispersion copolymerization of the vinylic monomer 2-(2′-hydroxy-5′-methacryloxyethylphenyl)-2H-benzotriazole (Norbloc (NB)) with the crosslinking monomer divinylbenzene. The effect of the initiator concentration on the size and size distribution of the polyNB (PNB) particles was elucidated. Thin coatings of the formed PNB NPs or MPs of 19 ± 2 and 200 ± 25 nm dry diameter, respectively, onto polypropylene (PP) films were then prepared and characterized. Increasing the concentration or thickness of the PNB NP or MP thin coatings on the PP films decreased their UV transmittance, up to complete UV blocking with just 2 μm of a 4% NP coating. Migration of the UV-absorbing agents from the coated PP films was not observed during three years of storage at room temperature, offering a unique solution to current problems of migration of UV-absorbing additives. The thin coatings obtained by the PNB NPs were superior to those of t...

Design of UV-Absorbing Polypropylene Films with Polymeric Benzotriaziole Based Nano- and Microparticle Coatings.

Polypropylene homopolymers and ethylene/propylene-random-copolymers formulated with and without anti-blocking additives were extruded to cast films with an industrial scale extruder equipped with a soft box, a specific air knife that expels a higher volume of air at lower velocity. The films were analyzed as to their optical properties haze and clarity. A comprehensive topographical characterization was performed using atomic force microscopy (AFM) and confocal microscopy. To obtain morphological information on a nanometer scale AFM phase imaging, micro-thermal analysis and small angle X-ray scattering (SAXS) were done. A significant effect of additives and processing conditions on the film topography and the optical properties was revealed. The films without anti-blocking and antacid aids showed the best optical properties and lowest vertical roughness fluctuations. In contrast, the addition of anti-blocking and antacid aids reduced the optical properties associated with an increase in surface roughness. While for films without anti-blocking aids an enhanced soft box condition resulted in lower vertical fluctuations of roughness and better optical properties, the behavior was in reverse for films with anti-blocking aid. By means of SAXS crystalline lamellae with a thickness of about 2.5 nm were detected. High-resolution phase imaging AFM yielded thicker crystal lamellae on the film surface. POLYM. ENG. SCI., 46:520–531, 2006. © 2006 Society of Plastics Engineers.

Optical properties of highly transparent polypropylene cast films: Influence of material structure, additives, and processing conditions

The relation between the surface topography of injection-molded plastic objects with deliberately imposed textures and their gloss, measured by means of a conventional glossmeter at incident angles of 20°, 60°, and 85°, was investigated. A modification of the general scalar Kirchhoff approximation, which accounts for geometrical features of the glossmeter, is used to describe the experimental gloss values of the textured surfaces. The agreement between the measured and the calculated values for incidence angles of 20° and 60° confirms the usefulness of the approach, though several of the textured surfaces used here are too rough for the Kirchhoff theory to be strictly valid. A poorer agreement, however, was noted at higher incidence angles (85° in this case). For very smooth surfaces (without any texture), the classical Bennett-Porteus theory could in many cases describe the gloss level with sufficient accuracy. The influence on the measured gloss of the polymer material (in terms of its refractive index) and the color of the injection-molded object is also discussed. Light beige specimens in three different polymeric materials (acrylonitrile-butadiene-styrene, acrylonitrile-butadiene-styrene/polycarbonate blend, and polypropylene) as well as three acrylonitrile-butadiene-styrene products with different colors were used. The refractive index of the polymer had no major influence on the measured gloss. The gloss level increased slightly with increasing lightness of the specimens, which can be associated with an increased contribution from the bulk scattering. However, the surface texture governed most of the gloss variations. POLYM. ENG. SCI., 45:1343–1356, 2005. © 2005 Society of Plastics Engineers

On the relation between surface texture and gloss of injection‐molded pigmented plastics

he haze of a film is defined as the fraction of (nor-mal incident) transmitted light that deviates fromthe directly transmitted beam by more than 2.5 (1).The contrast of an object seen through a film de-creases with increasing haze. The resolution of detail,a second criterion of transparency, is usually referredto as clarity. From a light scattering point of view,haze corresponds to larger scattering angles than lossof clarity. Note that a reduction in haze not necessarilyleads to improved clarity. Haze due to surface rough-ness is in many cases inversely related to gloss, whichis another important optical property.Both bulk inhomogeneities and surface roughnessmay contribute to haze. The latter effect usually domi-nates for polyethylene (PE) films. The typical scale ofthe roughness relative to the wavelength of light ( )determines the scattering characteristics. The heightvariation of the surface is usually reported to follow aGaussian distribution (2), and optical surfaces areoften characterized by the root-mean-square deviation( ) from the mean surface height. Roughness values, , in the range 20–600 nm are typically reported forPE films, i.e. . The haze increases monotonouslywith increasing roughness. Various techniques havebeen used for characterizing the surface profiles.Atomic force microscopy (AFM), has been applied in anumber of recent studies (3–6).Many types of PE are available for film blowingprocesses. The three main types, low-density (LDPE),linear low-density (LLDPE) and high-density (HDPE),all have their advantanges and drawbacks, also whenit comes to optical properties. Early experimental liter-ature (up to 1981) on the haze of PE blown films wasreviewed by Willmouth (1). The main findings can besummarized as follows. Two main sources of surfaceroughness have been identified: 1) flow-induced irreg-ularities originating from the die, and 2) protrudingcrystalline structures (lamellae, stacks of lamellae orspherulites). The former is a well-known rheologicaleffect, and the resulting extrusion-induced haze isoften observed to increase with increasing melt elas-ticity, e.g. due to more long-chain branching (LCB) or broader molecular weight distribution (MWD). The melt elasticity of LDPE (containing LCB) can be

Haze of polyethylene films—effects of material parameters and clarifying agents

A polyethylene composition comprising at least a first composition and a second composition in amounts of at least 70 wt% of the first composition which comprises at least: (A) up to 60 wt% lower molecular weight (LMW) polyethylene homo or copolymer obtained by Ziegler-Natta catalysis having a density of at least 940 kg/m ; and (B) up to 60 wt% higher molecular weight (HMW) polyethylene homo orcopolymer obtained by Ziegler-Natta catalysis and having lower density than component (A); and up to 30 wt% of the second composition which comprises: (C) a polyethylene homo or copolymer obtained bysingle site catalysis (SSC) and having a density of up to 980 kg/m ; wherein said polyethylene composition has a charpy impact strength at -20 DEG C, according to ISO 179-3 on compression moulded plates of at least 2.5 kJ/m and density at least 925 kg/m .

Composition, molded article, membrane and its preparation method and uses

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Haze of polyethylene films—effects of material parameters and clarifying agents

Composition, molded article, membrane and its preparation method and uses