Study On The Chemi-Mechanical Pulping And Bleaching Of Wheat Straw

Wheat straw is one of the most important papermaking materials in our country, which is very plentiful and cheap. The aims of this thesis are study on wheat straw pre-softened mechanical pulping systemically, and try to reduce the pollution during pulping and bleaching. The premium condition of pulping and bleaching has been found through the research on wheat straw chemi-mechanical pulping, and the fiber quality of wheat straw APMP has been analyzed as well.There are several factors affect wheat straw chemi-mechanical pulping, which includes charge of alkaline, temperature and time. And the effect of PaP bleaching is also studied. The results show that the suitable pretreatment condition is alkaline charge 6%, temperature 110oC, time 60min. Under such circumstance, the properties of pulp are as following: breaking length 3.89km, tearing index 2.58mN?m2?g-1, bursting index 2.61kP?m2?g-1. What's more, the result of PaP bleaching process is good, and the brightness is better when put Pa at the first step.The ratio of NaOH and H₂O₂ in wheat straw APMP is studied. The results show that the optimal ratio is 1.33, which can produce the highest brightness. In addition, the refining effluences of different processes were studied, and the result shows that the brightness increases at begin, and then decreases, however, the physical property get improved with the beating degree increasing.The effluence of factors in wheat straw APMP pulping is studied, as well as the comparison between single pretreatment and double. The results show that the alkaline charge and H₂O₂ is the two significant factors. The more charge of alkaline, the better the physical property of pulp, the more charge of H₂O₂, the higher brightness of paper. What's more, time, temperature and EDTA also can make properties of pulp different. With the same charge of reagent, the properties of pulp manufactured by double pretreatment are much better than by single.Complementary bleaching of wheat straw APMP is investigated. The results show that the optimal condition of ClO2 bleaching is charge 1.0%, temperature 30oC, time 30min, pH 3.0⁴.0. When use DP bleaching process, the brightness can get 70%ISO, however the physical property is bad, as long as the yield. DPa bleaching process can get 77.3%ISO, and the brightness and property can get better when divide the single D process into two parts. DPaP5 can make brightness 75.5%ISO, and the property of pulp is good, however the yield is lower, which is 87.9%. DPaP₃P₂ bleaching can get 76.5%ISO, and the yield is 89.2%. DPaP₅P₅ can get the highest brightness which is 77.3%ISO, and the yield is 85.4%.The fiber qualities of single pretreatment wheat straw APMP were analyzed by FQA. The results show that the fiber length gets increased with the alkaline charge increased, and the content of fine fiber is decreased, curl and kink is increased. The extent of change is significant when the alkaline charge increase from 4% to 6%. Increase H₂O₂ charge, prolong pretreatment time and increase temperature get the similar result, such as fiber length get increased, the content of fine fiber get decreased, curl and kink get increased, whereas the EDTA has nothing or very little effluence on fiber quality.