Characterization of Microwave Liquefied Bamboo Residue

Microwave Liquefaction System

Bamboo raw feedstocks with large particle size (20−80 mesh) were subjected to a microwave liquefaction system, and the liquefied products were separated into biopolyols and liquefied residues. Biopolyols were first analyzed by gas chromatography mass spectrometry (GC−MS), and the main components were sugar derivatives with 2−4 hydroxyl groups and phenolic compounds derived from lignin. The residues were collected and evaluated for potential use in the production of nanofibrillated cellulosic fibers. Results show that liquefied residue content as well as its physicochemical properties varied with respect to particle size, liquefaction temperature, and reaction time. It was also found that residues from liquefaction reaction with the minimum residue content in this study still exhibited traced fiber structure with remaining cellulose attached with recondensed lignin. Pure white cellulose fibers were extracted from the residues with yield of 65.61% using a combination of bleaching and acid hydrolysis treatment. Nanofibrillated cellulosic fibers were generated by given the purified cellulose fibers to high-intensity ultrasonic treatment. The resulted nanofibrillated cellulosic fibers had a range of 4−18 nm in diameter and length of 550 nm or longer, indicating the nanofibers obtained from liquefied bamboo residues hold great potential in reinforcing polymeric matrix materials. The successful isolation of nanofibrillated cellulosic fibers from liquefied residues offers a novel approach to make full use of the liquefied bamboo for value-added green products.

Biomass Feedstock

Biomass is widely considered as an important feedstock because of its renewability, ease of degradation, and availability. According to Perlack and Stokes, the current biomass resource availability annually was about 1.37 × 109 dry tons from forestlands and croplands.1 Recently, utilization of biomass for bioenergy or biochemicals has attracted great attention.2−6 For the production of biopolyols or biobased polymers, pyrolysis and liquefaction are two common pathways. However, liquefaction has more potential in converting biomass into valuable products because of its mild reaction conditions compared to pyrolysis.7−9 Liquefaction of biomass using organic solvents under conventional heating sources, such as oil has been carried out before, and the liquefied products have been also evaluated for the preparation of polyurethane foams10,11 and phenolic resins.12,13 Usually, in the conventional liquefaction system, inefficient thermal conduction on the surface of the feedstocks results in ineffective energy utilization, and very fine feedstock grinding (smaller than 200 mesh) was required because fine particles increase overall heat transfer in a certain extent.

Particle Size

However, this requires large amount of energy for size reduction, which in turn increases the whole energy consuming in the entire system. The application of microwave irradiation to wood liquefaction has been recently reported.14 Results have shown that microwave-assisted liquefaction could convert fine grinding wood feedstock into biopolyols with a high conversion yield (>90%) in minutes.15−17 This is mainly due to the fact that heating by microwave is direct and volumetric and thus results in efficient biomass conversion. Because of the benefits of microwave heating in wood liquefaction, various lignocellulosic such as wheat straw lignin,18 bamboo,19,20 sugarcane bagasse,21 and corn stover22 have been subjected to microwave-assisted liquefaction system for the production of biopolyols for alternatives of petroleum products. However, in all these studies only fine grinding feedstocks were used as raw materials, the attempts of using large particles has not been investigated.

Meet the Author

Dr. Todd Shupe is the President of Wood Science Consulting, LLC. He is a well-recognized expert on wood forensics, wood preservation, wood decay and degradation, and wood species identification. He has a broad background in new product development, quality management, and marketing and sales in both the public and private sectors. For more information please visit DrToddShupe.com.

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