Recycling of Polymers: Reprocessing of Multilayer Films
Multilayer plastics are often considered “unrecyclable” unless added to commmingled plastics recycling processes. Alternative reuse of these plastics has received little attention. The possibility of reprocessing multilayer plastics is examined in this work. Five-layer LDPE/nylon-6 films with an overall content of 71 wt% LDPE, 24 wt% nylon-6, and 5 wt% adhesive (a PE-based graft copolymer) were reprocessed under both minimal and extensive mixing conditions. Thermal and mechanical properties, oxygen and water vapor permeability, and morphology of the reprocessed films fell between those of the homopolymers, while average percent elongation at break and energy-to break for the reprocessed films were less than those of the hompolymers. However, minimally reprocessed film gave better mechanical results than extensively mixed samples. In the minimally reprocessed film, LDPE and nylon-6 layers were intact, whereas in the extensively mixed samples, nylon 6 domains were spherical and ranged form ~0.2-7 mm. Also, the minimally reprocessed film had excellent O2 and H2O vapor barrier properties, on par with as-received film.
Ageing of Polymers: In-Depth Degradation of Multilayer Polyethylene Slab
Multilayered slabs were formed by hot-pressing nine LDPE film layers. Weathering of samples was performed by a Q.U.V. apparatus, running dry at 55 oC for 147, 170, 284 and 340 hours. The in-depth degradation of LDPE via photo-oxidation was carefully studied following the carbonyl contents and retention of mechanical properties, mainly elongation and toughness, as a function of the distance from surface. Carbonyl contents, as measured by FTIR spectra, verified a parabolic symmetry around the center layer , which was least affected. Upon adding oxygen barrier layers on either side, or both sides of the slab, the rate of photo-oxidation was significantly reduced. The history of mechanical property retention follows a similar profile, but the outermost layers are slightly more affected (mainly those which are closer to the UV-radiation source). The conclusion is that photo-oxidation is primarily affected by diffusion of oxygen and that it is auto-catalytic.

J. Miltz, A. Ram, M.M. Nir, “Prospects for Application of Past-Consumer Used Plastics in Food Packaging”, Food Additives and Contaminants, 14, 649-659 1997.

A. Ram, “Fundamentals of Polymer Engineeirng”, Plenum Press, 1997.

G. Yanai, A. Ram and J. Miltz, “Accelerated Weathering Induced Degradation of Unprotected Polyethylene Slabs”, Part II, J. Appl. Polym. Sci., 59,1145-1149, 1996.

M. M. Nir A. Ram and J. Miltz, “Sorption and Migration of Organic liquids in PET” Polym. Eng & Sci., 36,862-868, 1996.

G. Yanai, A. Ram and J. Miltz, “Accelerated Weathering Induced Degradation of Unprotected Polyethylene Slabs”, Part I, J. Appl. Polym. Sci., 57 , 303-310, 1995.

A. Ram, M. M. Nir, J. Miltz, “Perfomance of Reprocessing of Multilayer LDPE/Nylon-6 Film” Polym. Eng. & Sci., 35, 1878-1883, 1995.

A. Ram, M. M. Nir and J. Miltz, “Reprocessed Multilayer LDPE/Nylon-6 Film” (Presented by A. Ram at Society of Plastic Engineers’ ANTEC Conference, New Orleans, LA, May 1993.