Role of molecular architecture in interfacial self-adhesion of polyethylene films

Abstract

The influence of molecular architecture on interfacial self-adhesion above polyethylene film melt temperature was examined in this study. The investigated molecular structures include molecular weight (Mw), molecular weight distribution, long chain branch amount and distribution and short chain branch among and along polyethylene chains. The long chain branches concentration was quantified using gel permeation chromatography and short branches concentration using nuclear magnetic resonance techniques. The adhesion strength was measured immediately after melt bonding using a T-Peel test. The results showed that increasing Mw resulted in higher adhesion strength in linear metallocene ethylene α-olefins. Low long chain branch concentrations hinder reptation motion and diffusion, and result in lower adhesion strength. Low density polyethylene with highly branched chains yielded very low self-adhesion. A drastic difference in adhesion strength between metallocene and conventional linear low density polyethylene is attributed to homogeneity versus heterogeneity of composition distribution. The low interfacial self-adhesion in conventional polyethylene was concluded to be due to enrichment of highly branched low molecular weight chains at the film surface. These segregated chains at the interface diffuse before the high molecular weight chains located in the bulk.

Understanding the factors affecting the seal integrity in heat sealed flexible food packages: A review

“…However, these may not provide strong adhesion and entanglement. 15 In the sealing of two different polymers, diffusion properties are strongly dependent on the compatibility of the two materials. When the packaging material is sealed to itself instead of different kinds of materials, interdiffusion rate will be equal to the self-diffusion rate.…”

“…However, the measured peel strength will differ before and after cooling for each polymer due to forming crystals, changing toughness and rheological properties of the materials. 15,20…”

“…However, that kind of polymer may create difficulties in determining the optimum process parameters to achieve full seal strength and result in lower adhesion strength during sealing. 15…”

“…Because the chain branching is directly associated with the movement ability of molecules through the molten media, it affects the diffusion rate under certain process conditions. According to Najarzadeh and Ajji, 15 LDPE samples containing highly branched molecules result in very weak seal bonding due to the inhibition of interdiffusion. On the other hand, small molecules having short chain branches can diffuse easier.…”

Troubleshooting and mitigating gels in polyethylene film products

“…A secondary circulation also develops in the channel stationary corner, creating a low-velocity helical eddy that is outside the high-velocity flows in the main channel. The interface between the main flow and the eddy flow is complicated due to self-adhesion 18 and is beyond the scope of this work. Figure 17 shows another degradation example caused by Moffat eddies for an LLDPE resin.…”