Synthesis of cellulose acetate butyrate based polymeric films and their applications

Cellulose is a bio-polymer that is the most abundant as raw material and is widely used in many commercial applications. The conversion of cellulose into regenerated cellulose can be occurred via the formation of ester and ethers by the reaction with various chemical species. In other words, the modification of raw cellulose, in the way of desired physical/chemical properties required for the usage area, is performed by adding functional groups. The hydroxyl groups that are extensively found in the cellulose structure, allow the mentioned modification processes. The most important commercially available cellulose ester derivatives are as follows; cellulose acetate, cellulose acetate propionate and butyrate, carboxymethyl cellulose acetate butyrate. Cellulose esters show various properties such as flexibility, rigidity, solubility, water/solvent resistance, bio-degradation, viscosity etc. depending on the chemical structure. This issue was given in literature review section in detailed. Besides the superior physical/chemical properties, cellulose esters have also some disadvantages that restrict their usage area. For instance, low solubility property of cellulose acetate in common solvents (ethyl acetate, 1,2-dichlorometan etc.), the hydrophobicity of carboxymethyl cellulose acetate butyrate, high viscosity of cellulose acetate butyrate in molten state and having low thermal stability. All these drawbacks of cellulose esters require the chemical modification processes or using them as blends with various polymers. Researches regarding to solve these drawbacks were given in further sections. As mentioned in literature review, the chemical modification of cellulose esters is important in terms of the synthesis of oligomers with desired properties that are suitable for the usage area. Among all cellulose derivatives, cellulose acetate butyrate (CAB) shows some superior properties such as high scratch resistance, suitable for food industry, and being economical. The CAB crystals in rod structure give a good gas barrier property. But, as mentioned before, the high viscosity of CAB in molten state restricts the processability property of CAB. Besides that, the low thermal stability of CAB leads a narrow processability range between the melting and decomposition temperatures. Researches regarding the solution of these problems are so limited in literature and there is no research considering the modification of the CAB by using urethane based oligomers. In this study, it was aimed to add UV-sensitive acrylate and carbamate ester groups to the CAB chain with the modification of toluene diisocyanate - hydroxyethyl methacrylate (TDI-HEMA) adduct via the hydroxyl groups in CAB structure, without changing the superior properties of CAB. The hydroxyl groups in CAB structure will be reacted in various percentages, and then the contribution of the hydroxyl groups, that are left unreacted, on adhesion and wettability properties will be investigated. The mechanical and chemical properties of UV-cured free films of TDI-HEMA modified CAB oligomers will be searched. Then the nano-fibers of these oligomers will be obtained by electrospinning method and cured by UV-light. The obtained nano-fiber surfaces will be investigated in terms of the gas/moisture permeability properties based on the standards (ASTM, ISO etc.) that are needed for food industry. Coating formulations will be prepared by using TDI-HEMA in various percentage reacted with hydroxyl groups on CAB oligomers. The effects of TDI-HEMA percentage on CAB morphological/mechanical properties, and gas/moisture permeability values of electrospun fibers surfaces will be observed. There are numerous researches regarding the nano-fiber production from cellulose derivatives and have been told in literature review. But the usage of UV-curing technology about this issue is so limited. The reason of using electrospinning method is that, the opportunity of an accurate controlling the coating thickness during the electrospinning process. UV-curing technology is favored due to the requiring none or less solvent (environment friendly), processability at low temperatures (economical), and saving of time with a rapid crosslinking mechanism just in a few seconds (mass production). In this study, the effects of urethane functionality percentage on coating formulations prepared by using TDI-HEMA modified CAB oligomers, the number of the hydroxyl groups left unreacted in CAB chain, electrospinning parameters on the properties of final product will be examined.