Study Of Bio-based Porous And Lightweight Composites Materials

With the increasing of resources shortage and environment problem, biomass energy has becoming the best substitute of fossil resources. Biomass materials have many advantages, such as renewability, biodegradability, abundant resource and extensive source.Compared with the traditional porous materials, the bio-based porous materials are not only have excellent mechanical, electrical, optical, acoustic and thermal properties, but also have many other advantages, such as renewable, biocompatibility and biodegradability. The opportunities and applications for bio-based porous materials in the field of chemical engineering, building materials, medicine and environmental protection are unlimited. In this article, the porous materials were fabricated by using cellulose, chitosan and agar as raw material and epichlorohydrin as crosslinking agent. The chemical structure and properties were characterized by the Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), coefficient of thermal conductivity meter universal mechanical testing machine and other modern analysis techniques.The main primary content of this work were shown as follows:(1) The chitosan/agar (CS/agar) and cellulose nanocrystals/chitosan/agar (CNCs /CS/agar) were prepared by freeze-thaw cycle method. The experimental results show that the water absorbency of CS/agar is 50 times when mass ratio of chitosan and agar is 4:3, and the water absorbency of CNCs/CS/agar is 45 times when mass ratio of cellulose nanocrystals, chitosan and agar is 4:57:43. Compared with CS/agar, the compression strength of CNCs/CS/agar was increased from 0.04MPa to 0.21MPa. It is shows that the porous material has good pH stability by pH stability test. And the density, coefficient of thermal conductivity and porosity of CNCs/CS/agar porous materials are 0.033g/cm"3,0.021 W·m-1k-1 and 98.6%, respectively. The results show that CNCs/CS/agar is a kind of thermal insulation material with high porosity, good water adsorption and lightweight.(2) The graphene was used as reinforcement for preparing graphene/CS/agar and graphene/CNCs/CS/agar porous materials, respectively. It shows that the sample still keep good water absorption even when the graphene content was 0.5%. The water absorbency of graphene/CS/agar and graphene/CNCs/CS/agar was 43 and 41 times, respectively. Moreover, the mechanical property of porous materials was improved by the addition of graphene. Compared with CS/agar, the compression strength of graphene/CS/agar was increased from 0.04 MPa to 0.23 MPa. And compared with CNCs/CS/agar, the graphene/CNCs/CS/agar were increased from 0.21 MPa to 0.58 MPa, and it was increased 5 and 2.8 times, respectively. The coefficient of thermal conductivity of the porous materials was increased after graphene addition. The coefficient of thermal conductivity of graphene/CS/agar is 0.052W·m-1·k-1, the graphene/CNCs/CS/agar is 0.045W·m-1·k-1. The samples all keep a good thermal insulation property. And it has a poor improvement of density, porosity and pH stability of porous materials.(3) Cellulose/agar aerogel was made of hydrogels by freezing drying, which was synthesized from agar in 4mol/L urea aqueous solutions and cellulose in NaOH/urea aqueous solutions by mixing with ECH as crosslinking agent. The test of morphology, compression strength and water (oil) absorption showed that the cellulose/agar porous materials have some advantages such as uniform porous structure, good resist compression property, water and oil absorbency. Due to the chemical crosslinking between cellulose and agar, the gel of agar can formed at 50 ℃. Because of the semi-rigid molecule chains of cellulose as a carriage in the system, the mechanical properties of cellulose/agar porous materials were improved. The cellulose/agar has high porosity (97.4%～98%), low density (0.036～0.044g·cm-3) and coefficient of thermal conductivity (0.042 W·m-1·k-1). Cellulose/agar is a kind of lightweight and good thermal insulation porous materials.(4) Cellulose/agar blends solution was dripped into the coagulation bath (comprised of 5%HCl and 5% CaCl2) to form spherical porous material. The effect of several operating parameters, such as initial concentration of MG, pH, contact time, temperature and NaCI concentration on the adsorption properties of cellulose/agar were investigated. The results show that the maximum adsorption capacity is 108mg/g when pH=4-5 and contact time of 7h. Absorption isotherm data can be imitated by the equation of Langmuir.