Weathering of Antibacterial Melt-Spun Polyfilaments Modified by Pine Rosin

For many antibacterial polymer fibres, especially for those with natural functional additives, the antibacterial response might not last over time. Moreover, the mechanical performance of polymeric fibres degrades significantly during the intended operation, such as usage in textile and industrial filter applications. The degradation process and overall ageing can lead to emitted volatile organic compounds (VOCs). This work focused on the usage of pine rosin as natural antibacterial chemical and analysed the weathering of melt-spun polyethylene (PE) and poly lactic acid (PLA) polyfilaments. A selected copolymer surfactant, as an additional chemical, was studied to better integrate rosin with the molecular structure of the plastics. The results reveal that a high 20 w-% of rosin content can be obtained by surfactant addition in non-oriented PE and PLA melt-spun polyfilaments. According to the VOC analysis, interestingly, the total emissions from the melt-spun PE and PLA fibres were lower for rosin-modified (10 w-%) fibres and when analysed below 60 ℃. The PE fibres of the polyfilaments were found to be clearly more durable in terms of the entire weathering study, i.e., five weeks of ultraviolet radiation, thermal ageing and standard washing. The antibacterial response against Gram-positive Staphylococcus aureus by the rosin-containing fibres was determined to be at the same level (decrease of 3–5 logs cfu/mL) as when using 1.0 w-% of commercial silver-containing antimicrobial. For the PE polyfilaments with rosin (10 w-%), full killing response (decrease of 3–5 logs cfu/mL) remained after four weeks of accelerated ageing at 60 ℃.

Effects of Prior Food Competition On the Rat's Killing Response To the White Mouse

Forty male albino rats were paired and given 15 trials in a dominance test situation where only one animal in a pair could eat at a given time. Length of time in control of the food and frequency of dominant gestures and failures, which involved either success or failure in displacing the other animal from the food source, were the criteria employed in determining the dominance relationship within a pair of animals. A second group of 20 animals, of the same age and strain, did not receive the competitive experience and served as a control group. The day following the termination of the dominance trials, an adult albino mouse was placed in the home cage of each rat in both groups. Results showed that: I. None of the rats in the non-competitive control group killed the mouse they were paired with. 2. Twenty-two of the rats in the competitive group killed. 3. Sixteen of the killer rats in the competitive group were dominant animals while only six were submissive. The results are explained as being due to the difference in past experience of the two groups of rats.