The Modified Hemp Stem Pulp And Preparation Of Cellulose Diacetate

Combined with the actual situation in our country, the author puts forward using hemp stem pulp to prepare cellulose diacetate for the first time, and researches the synthetic process.(1) After sodium hydroxide solution treatment the hemp stem pulp is analyzed. To the benefit of follow-up acetylation, the author determines the reaction conditions of alkali pretreatment:appropriate NaOH concentration is9%, and the temperature is20℃; the processing time is2.0hours. After the processes, fiber rate was65.00%; R-10value is93.70%; the degree of polymerization is423.15; iodine adsorption value is75.52mg/g.(2) With alkali treatment of hemp stem pulp as raw material, glacial acetic acid as dissolvant, sulfuric acid as catalyst and acetic anhydride as esterifying agent, the author synthetizes cellulose triacetate. The influence of sulfuric acid dosage, temperature, reaction time, acetic anhydride dosage, glacial acetic acid dosage is investigated respectively on the degree of substitution, the degree of polymerization of product. To prepare high degree of substitution and polymerization of cellulose acetate, the best condition is:glacial acetic acid with ultrasonic activation for1h, alkali treatment hemp pulp:glacial acetic acid:acetic anhydride (the ratio of quality)=1:10:9,catalyst dosage of sulfuric acid is13%of the hemp stem pulp after alkali treatment; reaction temperature is50℃; reaction time is1h.(3) The author uses acetic acid solution for hydrolysis reaction. When temperature rises to a certain temperature or time is long enough; the degree of substitution of cellulose acetate is lower. As the temperature increases and the time extends; the degree of polymerization declines.(4) To analysis the infrared spectrogram of cellulose triacetate and cellulose diacetate shows that3567-3496cm-1place is the characteristic of hydroxyl absorption peaks. After hydrolysis the telescopic vibration peak of hydroxyl cellulose diacetate is more than cellulose triacetate. After5h the telescopic vibration peak of hydroxyl of cellulose diacetate increases more than2h,at the same time the peak value is3567cm-1down to3496cm-1. DSC analysis shows that cellulose triacetate in160℃occurs glass transition. It explains that it is partial thermoplastic already. Cellulose diacetate in180℃appears glass transition, and glass transition heat peak of cellulose diacetate is more significant than cellulose triacetate.