Antimicrobial materials from cellulose using environmentally friendly techniques

Abstract: The transition to a more biobased society introduces both new opportunities and new challenges as we replace nonrenewable materials with renewable alternatives. One important challenge will be to control microbial growth on materials, both to protect the materials from biological degradation and to prevent the spread of infections and toxins that can cause illness.In this thesis, both existing and new types of cellulose-based materials were treated with environmentally friendly alternatives to usual biocides to prevent microbial growth and remove bacteria from water. Two types of antimicrobial systems were studied, and the antimicrobial effects were evaluated for bacteria and fungi using both model organisms and wild-type cultures.The first antimicrobial approach employed was a nonleaching and contact-active layer-by-layer adsorption of polyelectrolytes to provide the cellulose fibers with a cationic surface charge, which attracts and captures bacteria onto the fiber surface. The study showed that paper filters with pores much larger than bacteria could remove more than 99.9 % of E. coli from water when used in filtration mode. The polyelectrolyte-modified materials showed a good antibacterial effect but did not prevent fungal growth.The second approach was to utilize biobased compounds with antimicrobial properties, which were applied to cellulose fiber foam materials. Chitosan and extractives from birch bark were selected as biobased options for antimicrobial agents. Two types of cellulose fiber foam materials were developed and evaluated for their antimicrobial properties.This thesis shows the importance of understanding both the application and the targeted microorganism when selecting an environmentally friendly antimicrobial system for treating biobased materials. It highlights that a good understanding of both material science and microbiology is important when designing new antimicrobial materials.