Journal of Plastic Film & Sheeting

This paper presents the development of a method to measure damage to packaging laminates by penetration. A hemispherical probe was shown to provide the most reproducible results and the rate of loading was found to be a small factor. The puncture mechanism for different types of laminates was examined. It was shown that the presence of paper in the structure has a decisive effect on puncture resistance. For paper-based laminates, the paper layer limits the strength by rupturing first and then producing premature rupture of the other layers; the result is a 4-10-fold improvement in strength by eliminating paper as an outer layer. For laminates without paper, all layers rupture together so changing the composition of the non-paper layers has a direct influence on the puncture resistance. The direction of the penetration through the laminate usually has an effect on the energy to puncture.

A range of LLDPE films with polyisobutylene (PIB) content from 2-8% was manufactured using a Killion blown film extrusion system and a cast film extrusion system. The films were aged at 25, 35 and 45 C for up to 28 days, to enable tack (cling) development. The results show that tack, in both blown and cast films, improved significantly with ageing at increased storage temperatures and at higher film blow up ratios. DSC analysis showed only a slight decrease in film crystallinity with increasing PIB concentration. The film tensile modulus, elongation and tear properties in both MD and TD were not significantly affected by an increase in PIB concentration.

Film toughness measurements of certain ethylene-alpha-olefin copolymers of high impact strength, show significant aging effects, decreasing with time. In this work we studied the time and temperature dependence of film aging of several copolymers of varying molecular structure. Film aging appears to be associated with the presence of highly branched polymer chains (>30 branches per 1000 carbon atoms). It is speculated that the thermally activated rearrangement of such branched species, over time and under film storage conditions, leads to film aging. Higher film storage temperatures lead to faster aging. It is possible to employ an “accelerated aging” testing protocol to predict longer-term aged data from a short-term test, which would be useful in an industrial production setting.

Many applications are covered under this category, but the most typical are greenhouse covering, low tunnel film, mulch film, soil sterilization and fumigation film, silage film, film for water reservoirs, and film for packaging and protection. Although they have their application in the agricultural industry in common, they each have particular specifications and demands depending on the effects desired; these are described in this paper. Data is also provided concerning resin consumption and market share as well as the method of manufacture that is used for agricultural films, which are primarily made from polyolefins.

The stretch film industry has grown at phenomenal rates over the past 6-8 years. During that time, stretch film has evolved from monolayer to three layer and now commonly a five or seven layer product. This film is processed on equipment that varies in size and width along with other technological differences. This paper reviews the stretch film industry, outlines the major stretch film properties, and shows (by a case study comparison of two similar cast systems) how equipment and process variables can affect stretch film properties.