Research On The Preparation And Properties Of Cellulose-based Air Filters

The progressive seriousness of PM2.5 pollution and toxic gases pollution caused by the increasing enhancement of human activities has generated serious threats to human health.In addition,the accelerating depletion of fossil resources has limited the application of polymer-based materials.Given the health-attack problems and the environment concerns,the development of a new generation air filters with biodegradablity for replacing the popular polymer-based air filters has been a hot topic in academia and industrial filed.Cellulose-based air filter,a kind of biodegradable materials,has been regarded as a promising candidate to replace polymer-based air filter.It is worth noting for preparing a high-performance air filter,the control and design of pore structure is a key work during preparation process.Freeze-drying,a versatile and facile technique,has demonstrated many advantages in the preparation of cellulose-based porous materials.Therefore,in this research the facile freeze-drying technique was employed to explore the application potential of cellulose fibers,a green,renewable and biodegradable resource,in the preparation of high performance air filters.The main researches are as follows.Firstly,the effect factors during the preparation process of cellulose-based air filters using freeze-drying technique were studied.The results showed that the change of freezing temperature,the concentration of cellulose fibers suspension,or the fibrillation-treated degree of cellulose fibers all could cause to remarkable discrepancies in microstructure,pore morphology,and pore size of prepared cellulose-based filters by altering the growth pattern,morphology,and size of ice crystal,thus influencing the air filtration performance of air filters.The measurement of air filtration performance revealed that when the preparation conditions was set at freezing temperature of-56?,cellulose fibers suspension concentration of 1.5%,and refinging revolutions of 50000 r,the air filtration efficiency of preprared air filter for fine particle with the diameter of 300 nm was 65.12%,meaning failure to be used as a high-performance air filter.Secondly,for the preparation of more excellent air filter,Tert-butyl alcohol(TBA)was added into the mixture of fibrillated cellulose fibers/pure water to induce to form spider-web-like networks in the structure of final air filter.The results demonstrated that the role of TBA in the construction of spider-web-like structure can be ascribed to the following two aspects:(1)TBA molecules could promote the separation of microfibrils by weakening the intermolecular hydrogen-bonding interaction between different microfibrils and enhancing the chemical steric hindrance between adjacent microfibrils,thus favoring the formation of spider-web-like networks.(2)The presence of TBA could change the crystal structure and growth kinetics of ice-crystals,resulting in replacing the growth of large size lamellar ice crystals to the formation of pony-size TBA hydrates,thus transforming the microstructure of cellulosed-based air filters from an anisotropic lamellar porous architecture to an isotropic spider-web-like porous architecture.The measurement of air filtration performance indicated that the air filtration efficiency of spider-web-like air filters for fine particle with the diameter of 300 nm could reach to 99.07~99.78%,meaning succeed in meeting industrial N99 standard.Finally,the endowment of cellulose-based air filter with gas adsorpation capacity for purifing the toxic gases existing in polluted air was completed by modifying fibrillated cellulose fibers with ZIF-8 naoncrystals,a kind of MOFs materials with outstanding gas adsorpation ability.The measurement of air filtration performance showed that the filtration efficiency of ZIF-8 nanocrystals/cellulose fibers composite air filter for fine particle with the diameter of 300 nm could reach to 99.99%.The N2 absorption test revealed that the N2 absorption capacity of ZIF-8 nanocrystals/cellulose fibers composite air filter was 100 times higher than that of original cellulose-based air filter.The formaldehyde gas absorption test demonstrated that the formaldehyde absorption capacity of ZIF-8 nanocrystal-modified air filter at atmospheric pressure could exceed 30mg/g,which was 20 times higher than that of original cellulose-based air filter.