Four types of biaxially oriented polyamide 6 (PA-6) casings
with 45 mm of thickness were manufactured by ALICO S.A.
(Medellı´n, Colombia) as a multilayer film by bubble film sheet
co-extrusion (130 8C–14,000 kPa), identified according to the
layers distribution as control (PA/adhesive/PE-pigment/adhe-
sive/PA, with thickness distribution of 50/6.5/23/6.5/14% from
outside to inside layers) and active casings by adding 3% (w/w)
of a mixture of silver–zinc crystals fine powder (IRGAGUARD1
B7000, Ciba Specialty Chemicals Corporation, Tarrytown, NY,
USA), in the internal layer of the thermoplastic material.