Study On Pulping Technology And Mechanism Of Bamboo

Bamboo fiber is a green, environmental protective fiber, which has natural antibacterial and comfort properties. Developing new textile fabrics prepared by bamboo fiber could not only open up new way for producing cellulosic fiber, but also show great importance in solving the shortage problem of natural fiber and improving the productive level of fiber. In this paper, both hydrolysis and hydrolysis-kraft pulping process was studied by using Phyllostachys heterocycla cv pubescens, Dendrocalamopsis oldhami and Dendrocalamus latiflorus, which occured widely in Fujian province. In addition, the mechanism of pre-hydrolysis and pre-hydrolysis kraft pulping was studied, expecting to provide theory basis and technique support for developing the bamboo fiber industry.The average fiber length of Phyllostachys heterocycla cv pubescens, Dendrocalamopsis oldhami, Dendrocalamus latiflorus were 2.23mm, 2.19mm and 1.86mm respectively, cellulose content of them were 49.60%, 46.61%, 39.80%, acid insoluble lignin content of them were 30.52%, 23.12%, 20.32% and pentosan content of the bamboos were 21.32%, 19.78%, 17.45% respectively. The bamboos have longer fiber length, higher cellulose content and can be all taken as raw materials of bamboo pulp. Comparison differences of the three kinds of bamboos in the extractive content, acid insoluble lignin and pentosan content, Dendrocalamopsis oldhami has the highest cellulose content, the lowest content of pentosan and lignin. With all factors considered, Dendrocalamopsis oldhami is the best material to take the bamboo pulp between Phyllostachys heterocycla cv pubescens, Dendrocalamopsis oldhami and Dendrocalamus latiflorus.Pre-hydrolysis experiments of three bamboos were carried out to optimize the pre-hydrolysis process. The optimal hydrolysis conditions of Phyllostachys heterocycla cv pubescens were as followed: liquor ratio 1:4, heating rate 7℃/10min, holding time 90min, holding temperature 170℃, as a result, the hydrolysis product with yield of 73.62%, pentosan content of 11.02%, cellulose content of 53.46% was obtained. The optimum hydrolysis conditions of Dendrocalamopsis oldhami were: liquor ratio 1:3, heating rate 7℃/10min, holding time 90min, holding temperature 170℃, subsequently, the hydrolysis product with yield of 73.62%, pentosan content of 11.02%, cellulose content of 53.46% was obtained. The optimal hydrolysis conditions of Dendrocalamus latiflorus were: liquor ratio 1:4, heating rate 7℃/10min, holding time 90min, holding temperature 170℃, finally, the hydrolysis product with yield of 82.87%, pentosan content of 10.21%, cellulose content of 56.94% was obtained.Kraft pulping of prehydrolysis bamboos was conducted. The optimal kraft pulping processes of Phyllostachys heterocycla cv pubescens were: alkali charge 23%, sulfidity 23%, liquor 1:4, heating rate 7℃/10min, holding temperature 120min, holding tempereature 170℃, as a result, the pulp with yield of 25.40%, kappa number of 6.24, pentosan conten of 5.04%, ash content of 0.25%,α-cellulose content of 92.45% and viscosity of 16.57 mPa.s was obtained. The optimum kraft pulping conditions of Dendrocalamopsis oldhami were: alkali charge 23%, sulfidity 26%, liquor 1:4, heating rate 7℃/10min, holding temperature 90min, holding tempereature 170℃, subsequently, the pulp with yield of 38.82%, kappa number of 5.53, pentosan conten of 4.35%, ash content of 0.58%,α-cellulose content of 93.27% and viscosity of 17.45 mPa.s was produced. The optimum kraft pulping conditions of Dendrocalamus latiflorus were: alkali charge 23%, sulfidity 26%, liquor 1:3, heating rate 7℃/10min, holding temperature 90min, holding tempereature 170℃, subsequently, the pulp with yield of 29.63%, kappa number of 6.55, pentosan conten of 5.47%, ash content of 0.97%,α-cellulose content of 91.42% and viscosity of 25.63 mPa.s was produced.The mechanism of pre-hydrolysis and kraft pulping of Dendrocalamopsis oldhami was studied. Kinetic model of pre-hydrolysis was established. The results showed that, pentosan dissolving out from the bamboo during hydrolysis process was a first order reaction. When the holding temperature was 150℃, 160℃, 170℃, 180℃, reaction rate constants was 0.00411h-1, 0.00495h-1, 0.00730h-1, 0.00925h-1 respectively. Activation energy was 44.94 kJ/mol by calculation based on the Arrhenius empiric equation. SEM results revealed that, after pre-hydrolysis process, bamboo structure turned loosely because of dissolving out of hemicellulose, which created a favorable environment for cooking liquor to penetrate. Kinetic model of kraft pulping was established, lignin removing reaction belonged to two-order reaction. When the holding temperature was110℃, 130℃, 150℃, 170℃, reaction rate constant was 2.33×10-4, 3.14×10-4, 4.56×10-4, 6.98×10-4respectively. Activation energy was 25.77 kJ/mol by calculation based on the Arrhenius empiric equation. X-ray diffraction analysis result showed that, after kraft pulping process, degree of crystal of bamboo pulp was increased because of increment of cellulose content.