عنوان مقاله [English]
In this study, the properties of carboxymethyl cellulose made from waste paper were investigated. For this purpose, waste paper with different conditions was utilized to producing carboxymethyl cellulose, which included waste paper without ink and without bleaching (CMC-Ni), waste paper with ink and without bleaching (CMC-P), waste paper without ink and bleached (CMC-E). Also, industrial cellulose available in the market was utilized to producing carboxymethyl cellulose (CMC-Ic), and in order to compare the resulting samples, the properties of industrial carboxymethyl cellulose were also examined as a control. Infrared spectroscopy was used to investigate the chemical structure of carboxymethyl cellulose. And to investigate the manufactured carboxymethyl celluloses, the degree of substitution (DS), viscosity and pH of the samples were measured. The FT-IR results showed that the carboxymethyl celluloses obtained from waste paper have functional groups similar to industrial carboxymethyl cellulose, and the presence of ink and other impurities had no effect on their chemical structure. Carboxymethyl cellulose made from industrial cellulose showed differences in structure. The most important difference between cellulose and carboxymethyl cellulose is the presence of a peak at the wavelength of 1060/1 cm, which indicates the presence of carboxyl groups. Investigating the characteristics of the manufactured carboxymethyl celluloses showed that the degree of substitution of carboxymethyl cellulose is about 0.73 and the degree of substitution of carboxymethyl cellulose obtained from unbleached waste paper is about 0.69, which are not much different from each other. The viscosity of industrial carboxymethyl cellulose was higher than carboxymethyl celluloses made from waste paper. The characteristics of carboxymethyl cellulose obtained from bleached waste paper were more similar to industrial carboxymethyl cellulose. The pH of carboxymethyl celluloses was about 8 and very close to each other. In general, according to the obtained results, it can be concluded that the presence of ink and other impurities in the structure of waste paper does not have much effect on the characteristics of carboxymethyl cellulose, and by removing these steps, a simpler and more economical method can be used to produce carboxymethyl cellulose. Also, avoid from environmental pollution caused by these processes.
Considering the limitation of wood resources, one of the best solutions for supplying the raw material required by different industries is waste recycling. Converting wastes into useful products is very important. Waste recycling has many economic and environmental benefits. Paper is one of the important items used in the daily life of all sections of the society. The number of paper recycling in the paper industry is limited due to the decrease in the length of the fibers and it leads to a decrease in the tensile strength of the manufactured paper. Despite the prevalence of paper recycling, 30 to 40% of landfill areas in developed countries are still dedicated to waste paper. Utilizing waste paper in the production of cellulose derivatives is a suitable solution for reusing waste paper. Carboxy methyl cellulose and alkaline cellulose are the most important cellulose derivatives. Cellulose is a linear polymer with high molecular weight, which is naturally renewable and degradable. Due to the many hydrogen bonds in the molecular structure of cellulose, it cannot be easily melted or dissolved in water and common solvents. One of the ways to increase the applicatios of cellulose is to replace its hydroxyl functional groups with other functional groups and produce cellulose derivatives such as carboxymethyl cellulose, methyl cellulose and ethyl cellulose.
In this research, waste paper with different conditions (in terms of bleaching and presence of ink) was used to make carboxymethyl cellulose, and also carboxymethyl cellulose was made from industrial cellulose available in the market to determine the effect of the type of raw material on the properties of carboxymethyl cellulose. Also, industrial carboxymethyl cellulose was investigated and compared with manufactured samples. The codes of the treatments are defined in Table 1.
Production of carboxymethyl cellulose
100 ml of 99% isopropyl alcohol was added to 2 grams of dry paste, and after mechanical stirring, 20 ml of 40% sodium hydroxide was also added. Stirring in the reactor continued for 90 minutes. What remains after liquid phase separation is alkali cellulose. After this step, 3 grams of monochloro oacetic acid was gradually added to the reactor during 30 minutes at a temperature of 55°C, and the mechanical rotation continued for 210 min at the same temperature. Next, 70% methanol was added to the reactor and neutralization was carried out until pH equal to 7 with 90% acetic acid. After filtration, the resulting suspension was washed with 70% ethanol in 6 steps and finally with pure methanol. The resulting solid was dried at 60 °C and then ground.
• Investigating the properties of carboxymethyl cellulose
The chemical structure of fibers: In order to investigate the chemical structure of the manufactured carboxymethyl celluloses, the infrared spectroscopy test was used. For this purpose, an infrared Fourier transform spectrometer of the Organic Chemistry Laboratory of Mohaghegh Ardabili University was utlized. Measurement was done by potassium bromide tablet method.
Determining the degree of substitution: A sample of 5 grams of carboxymethyl cellulose was heated for 15 to 20 minutes at a temperature of 700 °C and the resulting ash reached room temperature in a desiccator. Then 6 ml of deionized boiling water was added to it to dissolve completely. The resulting solution is titrated with 0.1 normal sulfuric acid until the pH of the solution reaches 4.4.
Apparent viscosity: A Brookfield viscometer was used to measure the apparent viscosity of the carboxymethyl cellulose samples.
Determination of pH: It was done according to the GB/T 1904-2005 standard. First, the CMC solution was prepared with a dry percentage of 2%, and after it was completely dissolved, its pH was measured using a pH meter.
In this research, the possibility of producing carboxymethyl cellulose from waste paper under different conditions was investigated. The presence of ink and other impurities in the structure of waste paper has some effect on the characteristics of carboxymethyl cellulose, but the overall structure of the samples is the same, so by removing the bleaching and de-inking steps, it can be done in a simpler and more economical way. It was achieved for the production of carboxymethyl cellulose. Of course, considering the fact that the presence of chemicals limits the use of this type of carboxymethyl cellulose and it cannot be used in the food, pharmaceutical and health industries.