Chemical pretreatment is mainly cellulose and reaction reagent function in advance, by tolerating or swelling in order to increase the activity of cellulose surface (inner surface), to improve the micro pore structure, in order to improve the accessibility and reactivity, several methods described below.
Water: water is a kind of strong reaction of cellulose swelling agent, can disconnect the cellulose molecular chain, the hydrogen bonds between open pore structure, greatly increases the internal surface of the fiber, improve the reaction performance, so, in cellulose ether, quaternization, must have the presence of water.
Etc. Research shows that the water swelling of cellulose, its specific surface area can increase more than 50 times, the adiabatic acetify rate increases about four times. Water swelling, decide of chemical penetration, diffusion of diameter 5. Ox10m greatly increase the number of pores. In alkaline cellulose phase, water around the sodium ion hydration layer formation, swelling into the fibrillar, primitive fibrillar apart from each other, exposed birth of state all the accessible surface. Bolls of cotton fiber cell wall, saturated by water, primitive fibrillar apart from each other, known as the biological state of cotton fiber, cotton fiber moisture conservation value of 145%. When cotton linter left 16-18% NaOH aqueous solution at room temperature, Sodium Carboxymethyl Cellulose mercerizing, wash with water base and not dry, can be restored to its original biological condition of fiber volume fraction, water retention value of 115-118%, water swelling ability is very strong. But it must be very pay attention to the water swelling of sodium carboxymethyl cellulose is dry, as dry, molecular chain has broken hydrogen bond between bonded together, to the open pores tend to be closed by water, called keratinization, if the drying temperature is too high, dry too fast, will response performance than cellulose raw materials before water treatment response performance worse. Available water retention value (value) waterretention said the extent of the cellulose structure was opened after drying, Philipp determination of spruce wood sulphite hold moisture conservation, such as values, not dry (155%), 20 ℃ drying was 106%, under 105 ℃ drying was 77%, the drying under 150 ℃ 78%. So the pulp drying operation should cause enough attention.
Because there are a two-phase structure of cellulose fibre, amorphous and microcrystalline surface for reaction reagent and easily, high reactivity, crystal zone section for the large amounts of oxygen bond bonding between the molecules, the reagent is difficult to enter, poor reactivity. Jeffries, etc... Continuous methylation of cotton cellulose was studied, at the beginning of the reaction increases rapidly, mainly in the surface of crystal area, then response speed slow and close to a limit, one, two, three generated by the amount of methyl cellulose, estimates that about 44% of the water loss of glucose units in the original surface of fiber, about 56% of the water loss of glucose units in the original fiber inside, it will cause the chemical reaction process such as etherification highly inhomogeneity.
Philipp studied by liquid ammonia activation treatment of cellulose red ring of carboxymethylated reaction. Will be dried cellulose samples from 50 ℃ - O ℃ with liquid ammonia treatment under 30 minutes, and then under the 20 ℃ evaporation drying, after processing the samples ordered degree decline, increased accessibility, such as balance of degree of polymerization (LODP) fell from 160 to 85, water increased from 50% to 80% of water vapor balance adsorption value increases. Hydroxypropyl methyl cellulose with isopropyl alcohol as organic diluent, etherification 60 minutes under 60 ℃, Discussion of screw pregelatinized compared with the sample without activation treatment, active specimen under the condition of different proportion etherification, improved the degree of substitution.