Hydrogen‐Bond‐Induced Inclusion Complex in Aqueous Cellulose/LiOH/Urea Solution at Low Temperature

Cai, Jie; Zhang, Lina; Chang, Chunyu; Cheng, Gongzhen; Chen, Xuming; Chu, Benjamin

doi:10.1002/cphc.200700229

Cited by 190 publications

(106 citation statements)

References 36 publications

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“…In our laboratory, new solvents, such as aqueous NaOH/urea, NaOH/thiourea and LiOH/urea aqueous solutions have been used to dissolve cellulose at low temperature Cai et al 2007a;Ruan et al 2004;Cai and Zhang 2005). These solvents are attractable because cellulose can be easily and quickly dissolved them and produce stable cellulose solutions (Yan et al 2007).…”

Section: Introductionmentioning

confidence: 98%

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

2008

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Dissolution of cellulose having different viscosity-average molecular weight (M g ) in 7 wt% NaOH/12 wt%urea aqueous solution at temperature from 60 to -12.6°C was investigated with optical microscope, viscosity measurements and wide X-ray diffraction (WXRD). The solubility (S a ) of cellulose in NaOH/urea aqueous solution strongly depended on the temperature, and molecular weight. Their S a values increased with a decrease in temperature, and cellulose having M g below 10.0 9 10 4 could be dissolved completely in NaOH/urea aqueous solution pre-cooled to -12.6°C. The activation energy of dissolution (E a,s ) of the cellulose dissolution was a negative value, suggesting that the cellulose solution state had lower enthalpy than the solid cellulose. The cellulose concentration in this system increased with a decrease of M g to achieve about 8 wt% for M g of 3.1 9 10 4 . Moreover, cellulose having 12.7 9 10 4 could be dissolved completely in the solvent precooled to -12.6°C as its crystallinity (v c ) decreased from 0.62 to 0.53. We could improve the solubility of cellulose in NaOH/urea aqueous system by changing M g , v c and temperature. In addition, the zero-shear viscosity (g 0 ) at 0°C for the 4 wt% cellulose solution increased rapidly with an increase of M g , as a result of the enhancement of the aggregation and entanglement for the relatively long chains.

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Section: Introductionmentioning

confidence: 98%

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

2008

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“…Moreover, the sponges with relatively larger pores and dense wall were formed when the freezing/thawing cycles increased to 7 and 10 cycles, as shown in Figure 1c and d. It was not difficult to image the easy formation of the hydrogen-bonded network between starch and PVA, because they have abundant hydroxyl bonds and the hydrogen-bonded network structure was at a highly stable state at low temperature. [36][37][38][39] The starch and PVA were promoted to combine into the Effects of Freezing/Thawing Cycles and Cellulose Nanowhiskers . .…”

Section: Resultsmentioning

confidence: 99%

Effects of Freezing/Thawing Cycles and Cellulose Nanowhiskers on Structure and Properties of Biocompatible Starch/PVA Sponges

Wang

Chang

Zhang

2010

Macro Materials & Eng

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Strong honeycomb like nanocomposite sponges were fabricated from starch and PVA by using repeated cycles of freezing and thawing and reinforcing with cellulose whiskers. Their structure and properties were investigated with WAXD, FT‐IR, SEM, DMTA, rheological measurements, and LSCM. The results revealed that the repeated freezing/thawing cycles induced a physically crosslinked chain packing between starch and PVA, as well as a phase separation caused by the crystalline ice and syneresis. Thus, larger pores and tougher walls emerged in the sponges, leading to a high swelling degree. The sponges reinforced with cellulose whiskers exhibited improved dimensional stability and enhanced strength. These nanocomposite sponges are promising for wound dressing and tissue engineering applications.magnified image

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“…81,96 Soluções de NaOH/ureia, NaOH/tioureia e LiOH/ureia têm sido utilizadas para dissolver celulose em temperatura baixa. [97][98][99][100][101] Estes solventes são atraentes porque a celulose pode ser fácil e rapidamente dissolvida, produzindo soluções de celulose estável que podem ser usadas na preparação de membranas, por exemplo. 102,103 A utilização de solventes não-aquosos possibilita o uso de grupos sensíveis à umidade, os quais são adequados para a produção de uma série de derivados.…”

Section: Ligninaunclassified

Aplicações de fibras lignocelulósicas na química de polímeros e em compósitos

2009

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Recebido em 19/1/09; aceito em 25/3/09; publicado na web em 2/4/09 APPLICATIONS OF LIGNOCELLULOSIC FIBERS IN POLYMER CHEMISTRY AND IN COMPOSITES. The use of lignocellulosic fibers and their constituents, as raw materials in the production of polymeric and composite materials, represent an exceptional opportunity of sustainable technological development. In the present report works that discuss promising alternatives of obtaining and use of materials such as cellulose, hemicellulose, lignin, cellulose nanocrystals and biocomposites were revised. The advance in the use of biomass can be, in a near future, capable of going beyond the application difficulties of these vast materials, especially in relation to the economical unviability, by the production of high performance polymeric and composite materials. This advance would represent a higher profitability to some areas of agrobusiness, especially the sector of biofuels, which produces elevated amounts of biomass waste.Keywords: lignocellulosic fibers; nanowhiskers; biocomposites. introduçÃoNos últimos anos tem surgido um grande interesse mundial no desenvolvimento de tecnologias "verdes" que possibilitem a utilização de produtos de menor impacto ambiental.1-4 A química "verde", como um todo, implica no desenvolvimento de processos químicos e produtos que levem a um ambiente mais limpo, saudável e sustentável. Neste contexto, os materiais plásticos sintéticos têm recebido especial atenção por conter em seus métodos de preparação questões que devem ser priorizadas. As questões que devem ser priorizadas são a não-biodegradabilidade dos plásticos sintéticos e por serem oriundos de fontes não-renováveis. 5-8Na busca pela sustentabilidade, várias pesquisas e trabalhos na área de materiais poliméricos e compósitos foram, e estão sendo, realizados para garantir a preservação ambiental e proporcionar um melhor padrão de vida à sociedade.9-13 Dentre as pesquisas nesta área, as que buscam a aplicação de recursos naturais na preparação dos materiais vêm crescendo, podendo-se destacar o uso de fibras naturais. [14][15][16][17][18][19][20][21][22] A Organização das Nações Unidas para a Agricultura e a Alimentação (FAO-ONU -Food and Agriculture Organization of the United Nations) declarou o ano de 2009 como o ano internacional das fibras naturais.23 A medida visa conscientizar e estimular a utilização de fibras naturais, encorajando políticas governamentais de incentivo ao setor e às ações empresariais sustentáveis, para a exploração dessas matérias-primas.Destaque ainda maior deve ser dado à utilização de fibras naturais de origem vegetal, em razão da enorme variedade de espécies passí-veis de serem pesquisadas. Diversas fibras vegetais são produzidas em praticamente todos os países e usualmente são designadas como materiais lignocelulósicos. Algumas fibras ocorrem espontaneamente na natureza, outras são cultivadas como atividade agrícola e ainda há aquelas que são resíduos gerados, principalmente, pela agroindústria. Na Tabela 1 pode ser verificada a produção anual das princ...

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Hydrogen‐Bond‐Induced Inclusion Complex in Aqueous Cellulose/LiOH/Urea Solution at Low Temperature

Cited by 190 publications

References 36 publications

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

Effects of temperature and molecular weight on dissolution of cellulose in NaOH/urea aqueous solution

Effects of Freezing/Thawing Cycles and Cellulose Nanowhiskers on Structure and Properties of Biocompatible Starch/PVA Sponges

Aplicações de fibras lignocelulósicas na química de polímeros e em compósitos

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