Study On Preparation And Properties Of Highly Haze Transparent Cellulose Film

The transparent cellulose film is an emerging substrate for many electronic and optoelectronic devices such as solar cell,light-emitting diodes,touch screens because of its excellent optical properties,light weight,renewability,biodegradability and low cost.And highly haze and transparent substrate are beneficial to enhance the photoelectric conversion efficiency of solar cell.Therefore,it is very important to study the preparation and properties of cellulose film featuring with high transmittance and haze.In this paper,the dissolved pulp and bleached chemical pulp were used as the raw materials to pretreat by TEMPO oxidation.And the cellulose film was obtaied from TEMPO-oxidized cellulose treated by ultrasonication using solution casting method.The structure and properties of cellulose film was studied.?1?Wood dissolving pulp?Caribbean pine?was oxidized by using the TEMPO?2,2,6,6-tetramethylpiperidine-1-oxide radical?/NaBr/NaClO system.The effects of the conditions including pH,NaClO dosage,time on carboxyl groups,degree of polymerization?DP?,and solid recovery of oxidized cellulose were determined.A pH of 10 to 10.5 proved optimum for selectively oxidizing cellulose and carboxyl groups were up to 0.75mmol/g.However,an increase in pH from 9 to 12 facilitated cellulose depolymerization by consistently indicating a gradual drop in DP,thus resulting in cellulose loss.In addition,oxidation was accelerated by the addition of 1 mmol/g to 6 mmol/g NaClO;however,further addition did not enhance the carboxyl groups.The maximum value of carboxyl groups was more dependent on NaClO dosage and governed by the crystal structure of the raw material.To obtain oxidized cellulose with a higher yield and DP,NaClO dosage could be controlled at 4 mmol/g to 6 mmol/g,while the reaction time was limited to 6 h to 8 h.?2?The cellulose film was prepared from TEMPO-oxidized cellulose by by the casting method and ultrasonic treatment to improve the light transmittance and haze.It indicated that powerful ultrasonication effectively initiated severe cellulose fiber flattening,fibrillation,and cut off,and the size of cellulose fiber decreased with increasing ultrasonic power;therefore,films with small thickness,compact structures and smooth surfaces could be prepared,resulting in high transparency and tensile strength.By controlling the ultrasonic power within the range of180-360 W,transparent films?transmittance of⁹0%?with 51%-76%haze and a tensile strength?15-20 MPa?was obtained.?3?Bleached chemical pulp with different hemicellulose contents was prepared by cold alkali extraction using eucalyptus bleached chemical pulp as raw material.The effect of hemicellulose content on the TEMPO oxidation,cellulose fibers after ultrasonic treatment and the properties of cellulose film was researched.The results indicared that hemicelluloses content showed a negligible effect on TEMPO oxidation;while the prior alkaline extraction could significantly enhance the oxidation.Hemicellulose was advantageous for fibrillation of the oxidized fiber.In addition,the optical transmittance of cellulose film was almost constant at⁸9%;while the haze increased when more hemicellulose was present.In contrast,hemicellulose presence is much harmful for surface properties;it might be attributed to the rough.?4?The cellulose film was used as raw material to heat treatment under different temperatures and atmospheres.The results indicated that the light transmittance?92-87%?and tensile strength?21.16-0.25 Mpa?of cellulose film decreased gradually,but the haze increased gradually?77-84%?with the increase of heat treatment temperature in air atmosphere.When heat treatment at 100?,the light transmittance of cellulose film was over 89%,and the haze was higher than untreated cellulose film no matter under what kind of atmosphere.The light transmittance of cellulose film:untreatment>N₂>vacuum>Ar>Air,the tensile strength:untreatment>vacuum>Air>Ar>N₂.Therefore,using the prepared cellulose film as the substrate to prepare solar cell,the annealing processing can be treat under the vacuum condition of 100?.