Today in food packaging industry, cohesive peelable seals made from polymer composites are extensively used as easy-opening packaging. In this kind of films upon peeling, a crack initiates at the interface of the composite components and propagates through the seal layer. This approach results in a very strong and reliable seal in which the two webs of the seal are strongly welded together while, a low peel force is needed to open the package. While polymer blending is mainly used to produce this kind of packaging, using nanoparticles for easy opening packaging is a quite new topic and very few studies have been conducted on this issue. Due to the layered structure and high aspect ratio, nanoclays show considerable effects on the rheological, thermal, mechanical and barrier properties of homopolymers. Taking advantage of the high performances of the nanoclays, monolayer films with lower thickness and less material as well as easier and faster melt processing can be produced instead of multilayer films with the same level of seal properties. The dispersion and distribution as well as the affinity between matrix and nanoparticles are the main parameters that can be exploited to control the properties of the resulting nanocomposite seals including heat seal initiation temperature, peel force and heat seal temperature window.
In this study, nanocomposites of low density polyethylene (LDPE)/nanoclay with 1, 3 and 6 weight % of nanoparticle with and without polyethylene grafted maleic anhydride as compatibilizer were produced with twin screw extruder and then were filmed. The films were sealed using a heat sealer machine and then the peel behavior of the heat sealed samples were analysed using a tensile tester machine. X-Ray diffraction (XRD) was run on the films to study the level of dispersion of the nanoclay in the nanocomposites. Linear viscoelastic behavior of the pure LDPE and nanocomposites were measured in order to evaluate the interaction between nanoparticles and polymer. Differential scanning calorimetry (DSC) was used to study the effect of nanoparticles on the melt temperature and crystallinity of the films and consequently on their seal and peel behavior.
Nanocomposites without compatibilizer showed tactoid dispersion. The heat sealed films made with LDPE are lock seals and the failure mode is material break while peeling of the nanocomposites with no compatibilizer showed that the failure mode at the beginning of the peel is cohesive peel and then transfers to material break. Presence of the compatibilizer in the nanocomposites results in intercalated dispersion with a failure mode of cohesive peel. The nanocomposites also revealed very wide heat seal temperature window and lower heat seal initiation temperature compared to sealants of pure LDPE.
It is concluded that the seal and peel behavior of the nanocomposite sealants significantly are affected by dispersion and distribution of the nanoparticles in polymer matrix.