Heat Seal Modifiers

Low density poly(ethylene) (LDPE) may have unsatisfactory heat seal properties, as they often do not provide sufficient adhesion between the sealing layers to result in a good adhesive seal for a package. Efforts to improve the heat seal characteristics of LDPE by blending them with other materials, such as ethylene copolymers with methacrylic acid or acrylic acid, have not had universal success. 

Special PE formulations, including ionomers and poly(terpene) tackifiers have been presented (18). The individual components are melt blended in an extruder. 

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G.M. Lenges and T.A. Libert, Heat seal modifiers for linear polyethyl-enes, US Patent 7 635 736, assigned to E. I. du Pont de Nemours and Company (Wilmington, DE), December 22,2009. 

Stretch bundling can apply to single products or packs, or groups of somewhat irregular loads. The film is normally stretched around the product to give a tight wrap with up to 25% stretch. The material finishes with an adhesive or heat seal. Modified LDPE, VLDPE or EVA are normally used. 

The above results suggest a potential for utilizing surface fluorinated plastics for modified atmosphere and vacuum packaging applications. If needed, the barrier properties can be improved further by vacuum metalization. Excellent adhesion was found for vacuum-deposited aluminum on this new fluorinated layer, achieving an adhesion index of 10 using the classical cross-hatch method. With this treatment method it was also possible to heat-seal PP or PE onto PET. 

In a random copolymer, the monomers are randomly distributed along the chain, so there is no pattern to their arrangement (Fig. 3.4). For example, random polypropylene copolymers are a type of polypropylene in which the basic structure of the polymer chain is modified by the incorporation of ethylene comonomer during the polymerization process. This results in changes in the physical properties compared to homopolymer PP such as increased clarity, improved impact resistance, increased flexibility, and a decrease in the melting point and heat sealing temperature. 

Uses Polyrner modifier used with all polyolefins for specialty tilms/lami-nates, fabric coatings, medical films, disposable gloves Features Provides soft, rubber films, exc. toughness, broad heat seal range, controlled flexibility... 

Chem. Descrip. Methyl methacrylate/modified PVC-based polymer Uses Heat-sealing raw material for pkg. of foods and pharmaceuticals adhesive/bonding agent for finishing PVC leatherette and film binder in printing inks and spray paints for PVC, ABS, PS coatings and films Properties Bead in powd. form sol. in ethyl acetate, MEK, acetone, cyclohexanone, butyl acetate, butyl glycol acetate, aromatics, tetrahydro-furan, chlorinated hydrocarbons insol. in naphtha and alcohols dens. 1.36 g/cm reduced vise. 45-55 em /g (20 C)... 

CAS 12738-64-6 EINECS/ELINCS 235-795-5 Uses Plasticizer, gloss aid for clear coatings for wood/paper/metal. me-tallic/pigmented coatings, heat-seal coatings, and inks modifier, gloss aid for clear lacquers... 

Methanethiol. Methanethiol was a major volatile sulfur compound formed in broccoli florets stored in sealed jars for 7 days at 15°C which developed severe off-flavors, and it was considered the most important contributor to the objectionable odors that render the modified atmosphere stored broccoli florets unmarketable (14). Similarly, we observed that broccoli florets stored in heat-sealed barrier pouches (15 cm X 25 cm o.d. 70 g/bag Curlon X/K-28 Grade 850 Curwood, New London, with oxygen transmission rates less than 1 cc 02/645 cm /24 hr developed offensive sulfurous odors within a few days storage at 4 C. 

Modified Atmosphere Stored Broccoli Florets. Since TBHQ and caraway seed flavonoid components exhibited the same effect on depletion of methanethiol in model systems, they were examined for efficacy in suppressing methanethiol-related off-flavors in broccoli florets stored under modified atmospheres. Freshly prepared broccoli florets (ca 3 cm long) were treated by dipping them in cell-free cni caraway seed extracts or aqueous TBHQ solutions (100 ppm), and allowing excess liquids to drain off. Control samples were dipped in distilled water. Broccoli samples were placed in the heat-sealed Curlon 850 pouches described earlier (70 g/pouch), and then held under refrigeration at 4°C until used for GC-FPD and descriptive sensory analysis 8 days later. 

At elevated temperatures, the ester loses its inactive role as modifier-extender and functions as plasticizer or even solvent for some polymers. This bifunctional property makes it a valuable component of heat-seal coatings and hot-melt adhesives. 

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