The moisture barrier and heat sealability properties of polylactide (PLA) extrusioncoated paperboard were investigated. The fi rst part of the study focused on the infl uences of coating weight and surroundings temperature and relative humidity on the water vapour transmission rate (WVTR) of the structure. The outcome arising from this part was a simple and practical equation that allows calculating the WVTR as a function of PLA coating weight under specifi c thermo-hygrometric conditions. The second part of the study investigated the effect of heat treatments between 100 and 150°C on the WVTR and heat sealability of a 20 g/m 2 PLA-coated paperboard. According to the results, the lowest WVTR values achieved were about 2.5 times lower than the WVTR of the untreated structure. Presumably, the PLA coating experienced two types of reordering mechanisms: crystalline growth and packing of the amorphous structure. The greatest barrier improvement was achieved when both of these mechanisms were accumulated effectively. This was observed from the samples after a 40 min treatment at 130°C. Ultimately, the crystalline growth was experienced by PLA at 100-130°C temperatures. The packing of the amorphous section, which was also accumulated at higher temperatures, was suggested to be the decisive factor infl uencing WVTR. According to the heat sealing results, the heat treatments causing crystalline growth resulted in considerably increased sealing temperatures and reduced applicability of the material in high-speed packaging applications. The treatments at 140-150°C caused only a slight increase in the sealing temperature and maintained the sealing performance of PLA.

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The effect of various fillers on the mechanical, barrier, and flammability properties of polypropylene (PP) was studied. PP was filled with 4 wt% of nano‐sized calcium carbonate, titanium dioxide, organoclay, and multiwalled carbon nanotube (MWCNT). For comparison, micron‐sized calcium carbonate was also studied. Two‐step masterbatch dilution approach of the composites suggested no or only minor improvements in Young's modulus and tensile yield strength, whereas their ductility decreased compared to coupling agent‐modified PP matrix. The water vapor transmission results of filled films showed increased permeability compared to their coupling agent‐modified counterpart. Oxygen permeability, however, decreased for the composites. The MWCNT‐filled matrix showed the highest barrier and fire performance, attributed mainly to its higher filler volume content, but also other reasons such as the effect of filler dispersion, composite's thermal stability, and polymer crystallinity were discussed.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers

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