Effects of UV weathering on the mechanical and antibacterial performance of peroxide‐cured silicone rubber containing biocide HPQM

2‐Hydroxypropyl‐3‐piperazinyl‐quinoline carboxylic acid methacrylate (HPQM) was used as a biocide in a silicone rubber compound. Antibacterial and mechanical performance of the compound was assessed before and after exposure to UV light for different times. Drop‐plate and halo tests were employed to evaluate qualitatively and quantitatively the antibacterial performance of the compound against Escherichia coli (E. coli, ATCC 25922) and Staphylococcus aureus (S. aureus, ATCC 25923). The results showed that the cure characteristics and the physical and mechanical properties of the HPQM‐containing rubber compound were strongly affected by the UV light. The tensile properties and hardness increased with UV aging. The lightness (L*) of the rubber compound without HPQM did not change with UV exposure, whereas that for the compound with HPQM decreased with UV exposure. The longer the contact time, the better the ability for killing the bacteria. After experiencing initial UV aging for 3 days, the rubber compound with HPQM showed an effective killing ability. However, after prolonged UV exposure, the antibacterial efficacy was reduced as a result of HPQM removal from the rubber surface during the condensation stage and a post‐curing reaction of the residual peroxide in the rubber compound. Under UV light, the silicone rubber compound with HPQM had a greater preference for killing the E. coli. J. VINYL ADDIT. TECHNOL., 20:49–56, 2014. © 2014 Society of Plastics Engineers     

Effect of organoclay and silver‐substituted zeolite on the mechanical and antibacterial properties of a silicone rubber filled with 2‐hydroxypropyl‐3‐piperazinyl‐quinoline carboxylic acid methacrylate

Silicone rubber compounds filled with different loadings of organoclay (OC) and silver substituted zeolite (SSZ) solid fillers were prepared and cured with 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane. The rubber vulcanizates contained an antimicrobial agent to protect them against Escherichia coli (E. coli ATCC 25922) and Staphylococcus aureus (S. aureus ATCC 25923) bacteria. The tensile strength, elongation at break, stored energy density at break, Young's modulus, modulus at 100% elongation, cyclic fatigue life, and glass transition temperature of the rubber vulcanizates were subsequently measured. The antimicrobial performance of the rubber surfaces were determined by disk diffusion testing and plate count agar method. The antimicrobial agent had an adverse effect on the mechanical properties, but the cyclic fatigue life of the rubber vulcanizate improved. The addition of OC and SSZ could improve the tensile strength, elongation at break and stored energy density at break, but deteriorated the tear energy, Young's modulus and modulus at 100% elongation. The inclusion of the fillers was not beneficial to the antimicrobial activity of the rubber against bacteria. The HPQM in the rubber was effective more against E. coli. than against S. aureus. Furthermore, the antimicrobial activity increased when the contact time in the test solution was increased. POLYM. ENG. SCI., 54:932–941, 2014. © 2013 Society of Plastics Engineers     

Antimicrobial performance and the cure and mechanical properties of peroxide‐cured silicone rubber compounds

Nanosilver colloid, Ag‐based zeolite compound, and 2‐hydroxypropyl‐3‐piperazinylquinolinecarboxylic acid methacrylate (HPQCAM) were used as antimicrobial agents and/or mechanical property improvers in peroxide‐cured silicone rubber vulcanizates. The vulcanizates were prepared by using a two‐roll mill followed by a hydraulic press in order to vulcanize the rubber compounds, and their cure characteristics, mechanical properties, and antibacterial performance were assessed. The antimicrobial performance of the silicone rubber compounds was examined through plate‐count‐agar and drop‐plate‐agar methods, as well as the halo test. The results suggested that the addition of all of the antimicrobial agents slightly increased the cure time, except for the Ag‐based zeolite. The addition of all of the antimicrobial agents also affected the mechanical properties of the rubber vulcanizates. The Ag‐based zeolite gave the silicone rubber compound with the most improved mechanical properties, whereas HPQCAM was the most effective antimicrobial agent, as determined by the occurrence of the inhibition zone and 99% reductions of Staphylococcus aureus and Escherichia coli. The changes in silicone rubber surface with the addition of antibacterial agent were shown by progressive decreases in water contact angle. This result was observed only for the HPQCAM agent and was associated with diffusion and the releasing mechanism of the HPQCAM to kill the bacteria. The optical lightness of the silicone vulcanizates decreased with increasing nanosilver content but increased with increasing amounts of Ag‐based zeolite or HPQCAM. J. VINYL ADDIT. TECHNOL., 19:113–122, 2013. © 2013 Society of Plastics Engineers