Polymers are used in many industrial areas due to their longevity and inexpensive production, as well as their many advantageous physical and chemical properties. The low recycling rate of polymers, however, makes them harmful to the environment. Biopolymers from renewable raw materials are a sustainable alternative to polymers from finite raw materials, such as crude oil. Such biopolymers are CO2-neutral and can be bio-degradable. On the other hand, their mechanical properties are often inferior in comparison with those of crude oil-based polymers.
In our work, we prepared biopolymer films from potato starch, corn starch, chitosan, and casein. The wet thickness of the films was optimized to enable them to be detached from the glass substrate without damage. Both starch films were found to be more elastic and stretchable than the chitosan and casein films. The casein film was more stable than the chitosan film, which showed small air cavities during drying.
Afterwards, all biopolymer films were coated by electrospinning. To achieve this, the wire-based electrospinning machine “Nanospider Lab” (Elmarco) was used. Spinning solutions were prepared from 16% poly(acrylonitrile) in dimethyl sulfoxide (DMSO). Electrospinning of the films was performed for 30 min under optimized conditions. The nanofibrous mats adhered well to the biopolymer films during electrospinning, but could be mechanically separated afterwards.
A universal testing machine was used for the mechanical tests. Although nanofiber mats usually do not have very good mechanical properties, the composites made with biopolymer and nanofibrous coatings showed significantly improved tensile strength, as compared to the pure biopolymer, for all materials under investigation. The results of this project can be used to prepare biopolymer films with significantly improved mechanical properties, e.g., for packaging applications or wound dressings.
