Green Preparation Of Nanofibrillated Cellulose From Waste Cotton Fabric And Its Application In Hydrogel

Nanofibrillated cellulose(NFC),derived from lignocellulosic materials,inherits the advantages of a wide range of common cellulose resources,e.g.,renewable,degradable,non-toxic characteristics and has excellent barrier,mechanical and colloid properties.It has shown great promise in devisified application fields,such as papermaking,composite materials,packaging,coatings,biomedicine,automotive and other fields.Nowadays,with the deepening of people’s understanding of environmental issues,more and more attention has been paid to comprehensive utilization of wastes as well as green and efficient preparation methods.Typically,waste cotton fabric is characteristic of low price and rich in cellulose and might be expected to become a substitute of raw materials for NFC production.Based on this,in the present work,the waste cotton fabric used as raw material and an environmentally friendly process were employed for NFC preparation.The proposed concept would contribute to the environmental protection and the achievement of high-value-added products,which could essentially broaden the source of raw materials for NFC preparation and provides a new idea for the green and efficient preparation of NFC.Firstly,NFC was extracted from industrial waste cotton fabrics via deep eutectic solvent(DES)pretreatment combined with the ball milling process.The appropriate main process was obtained as follows:DES pretreatment temperature 110℃,pretreatment time 3 h,ball milling time 16 h,and the NFC yield based on the above process was 49.7%.SEM results showed that the as-prepared NFC samples exhibited a diameter of 30-60 nm,a length of 1-2μm,and an average particle size of about 953 nm.With the increase of ball milling time,NFC yield showed a slight increase,and the particle size distribution of NFC sample appeared to be more uniform.According to FT-IR and XRD analysis,it can be found that DES pretreatment and ball milling treatment did not change the crystal structure of NFC.XRD and TG analysis results showed that the prolonged pretreatment time and the elevated pretreatment temperature led to the reduced crystallinity and thermal stability of the NFC samples.Secondly,sodium alginate(SA)and chitosan(CS)were used as the main raw materials for composite hydrogel preparation.NFC was used as the reinforcing phase to improve the overall properties of SA/CS/NFC composite hydrogel.In detail,the influence of the mass ratio of SA and CS on the performance of poly-ion SA/CS composite hydrogels was investigated.It was found that as the mass ratio of SA/CS increased,the ion pairs of SA and CS reactions also increased.Furthermore,the storage modulus,loss modulus,and compound viscosity showed an upward trend and then a downward trend as a function of the increased SA/CS ratio.When the mass ratio was 5:4(corresponding to an ion pair of about 1:1),the mechanical properties of the SA/CS/NFC hydrogel reached a maximum.When the mass ratio was 5:5,the swelling performance of the SA/CS/NFC hydrogel achieved the best.Particularly,with the increased incorporation of NFC,the storage modulus,loss modulus,and composite viscosity of the SA/CS/NFC hydrogel firstly increased and then decreased,and the swelling properties decreased correspondingly.Specifically,the addition of 1%NFC was found to be effective in reinforcing the composite hydrogel.Finally,the pH response of the SA/CS/NFC composite hydrogel was investigated by loading IND drugs,and the sustained release behavior of the composite hydrogel in simulated human gastrointestinal juice was preliminarily studied.The results showed that the SA/CA composite hydrogel exhibited different swelling properties in different pH buffers,which provided evidence that the hydrogel had a certain pH response performance.The addition of NFC did not change the pH response performance and drug loading of the hydrogel,but only reduced the swelling rate of the hydrogel to a certain extent.SA/CS/NFC composite hydrogel had a good sustained-release effect in simulated human gastrointestinal juice,and the release time was 12-24 h.By changing the amount of NFC added,the release amount and release rate of IND changed significantly.The release mechanism of IND demonstrated that the release of SA/CS/NFC was found to be generally consistent with the zero-order drug release model in simulated gastric juice and R-P model in the simulated intestinal fluid.As a result,it could be concluded that SA/CS/NFC hydrogel generally has the potential to be acted as a drug carrier.