Traditional food preservatives, sodium benzoate, sodium nitrite, potassium sorbate and sodium lactate, were incorporated into synthetic plastics, low-density polyethylene (LDPE), poly(maleic acid-co-olefine), polystyrene (PS) and polyethylene terephthalate (PET), aimed at producing antimicrobial packaging material for foodstuffs. The study was undertaken on plaques (thickness 2 mm) and films (thickness 70-120 mm), whose antimicrobial test results clearly differed. Plaques containing 15% sodium nitrite inhibited both Aspergillus niger and Bacillus subtilis, whereas the same concentration of sodium benzoate and potassium sorbate had activity only against B. subtilis. Sodium lactate-containing samples did not have any antimicrobial activity and none of the samples inhibited Escherichia coli. Antimicrobial substances added into PS and PET produced the strongest activities; however, due to the brittle structure of these materials, they were not tested further. Thus, more thorough tests for antimicrobial activity, migration and oxygen and water vapour permeability were carried out using LDPE films with 2.5-15% sodium benzoate and sodium nitrite. The effects of both substances on permeability properties were negligible. Although the total migration into food simulants measured from the films in many cases exceeded the limit value of 10 mg/dm 2 , no antimicrobial activity was observed.
Imazalil and ethylenediamine-tetraacetic acid (EDTA) were incorporated into low-density polyethylene (LDPE) aimed at producing antimicrobial packaging films for foodstuffs. Moulded plates (thickness 2mm) containing 5% of EDTA inhibited Bacillus subtilis, whereas 0.05–0.25% of imazalil had strong activity against Aspergillus niger. Further tests for antimicrobial activity, migration and oxygen and water vapor barrier properties were carried out using biaxially stretched LDPE films containing different combinations of both substances. The addition of imazalil and EDTA increased the oxygen transmission rates and water vapor permeabilities, although the effects with imazalil films were not as significant. Transparency of the EDTA containing films decreased rapidly as a function of added EDTA, whereas imazalil films were optically faultless. Total migration into 3% acetic acid and 10% ethanol was below 4 mg/dm2. Although imazalil retained its activity against A. niger on a high level (inhibition zones >30 mm), the activity of EDTA was gone. None of the samples inhibited Escherichia coli.
An advanced injection molding tool for measurement of mechanical strength and anisotropy of liquid crystal polymers (LCP)/mineral filler composites was developed. The mold produces thin-walled LCP specimens that can be used by water cutting technique for production of an injection molded flow direction test bar, a transverse-to-injection molded flow direction test bar, a test bar for knit line strength measurement, and a test bar for butt weld line strength measurement. This tool and its use for molding experiments were optimized by experimental research and by computational calculations based on experimental parameters obtained by molding of several LCP test materials. Different pressure profiles and different injection speeds were tested as well as application of mold overflow phenomenon in production of test specimens. It was observed that a pressure controlled X-melt technique and on the other hand fast injection speeds with overflow in conventional molding methods gave the best strength and isotropy properties for the test specimens. Results indicate that the mold developed is useful for determination of anisotropic and weld line strength properties of LCP composites. When developing ''isotropic LCP'' by different possibilities of nanotechnology this tool significantly reduces time of LCP material and process development. POLYM. ENG. SCI.,
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