Heat sealing of LLDPE: relationships to melting and interdiffusion

Abstract

ABSTRACT:The effect of heat sealing variables (platen temperature and dwell time) on seal strength of a linear low-density polyethylene (LLDPE) was examined. In order to characterize the development of interfacial strength, blown films were heat-sealed for times from 1 to 100,000 s, much longer than the typical sealing times of less than 1 s. The seal temperature ranged from 100 to 130°C. From the differential scanning calorimetry thermogram, the LLDPE was determined to be completely melted at 130°C. Therefore, the films ranged from partially to fully melted when they were heat-sealed. The seal strength was measured in the T-peel configuration, and the peel fracture surfaces were examined in the scanning electron microscope. A temperature of 115°C or higher was required to form a good seal. The strong effect of seal temperature was related to the heterogeneous composition of the LLDPE studied. At 115°C, the lowermolecular-weight, more highly branched chains easily diffused across the interface. Crystallization upon cooling produced connections across the interface. However, because these chains represented a small fraction of the crystallinity and the molecular weight was low, they contributed much less than the full peel strength. Conversely, chains with less branching represented the main fraction of crystallinity (anchors for tie chains) and the highest molecular weights (more entanglements). Only at temperatures at which the higher-molecular-weight, less branched chains began to melt and diffuse across the interface could high peel strengths be achieved.

Atmospheric pressure plasma treatment of amorphous polyethylene terephthalate for enhanced heatsealing properties

“…APET Sheet Material This layer has a lower melting temperature than that of the top film and thus during the heatsealing operation when this layer is brought into contact with the food tray it is melted, thereby sealing the top film to the food tray [2]. An example of this heatseal layer is low density polyethylene (LDPE), which is co-extruded with the polyethylene terepthalate (PET).…”

“…In the heat sealing process a polymer top film is applied to the polymer tray under elevated temperature and pressure in order to enclose the food product in an airtight environment [2]. The conventional method for creating a strong bond between a food tray and a top film is to use a co-extruded heatseal layer ( Figure 1).…”

Tailored Polyethylene Nanocomposite Sealants: Broad-Range Peelable Heat-Seals Through Designed Filler/Polymer Interfaces

“…The high sealing pressure and long dwell time ensure equilibration of the temperature at the sealing surface (interface) independent of film thickness and composition [21,23] (see Note 2).…”

“…3b). According to these DSC melting traces, heat sealing temperatures between 90 • C and 150 • C should be effective for the sealants used [23].…”

“…Polyethylene (PE) has a large market share in the plastics packaging market, as it is widely used in food, medical and cosmetic products, and also as a sealant with peelable or weld (fused) seals [21][22][23][24][25][26]. However, in contrast with polar and/or thermosetting polymers, non-polar polymers -such as polyolefins -still present a challenge in preparing well-defined melt-processable nanocomposites with layeredsilicates [27,28]; they typically require a two-step processing via dilution of a masterbatch, i.e., a concentrate of a layered-silicate or clay predispersed in a functionalized form of the same polyolefin.…”