Development of the fastest drying oxidized starch

Development of quick drying oxidized starch adhesive for corrugated board

[Abstract] the oxidized starch adhesive for corrugated board was developed by using corn starch as raw material to oxidize and prepare starch phosphate, together with catalyst, drier and preservative. The drying speed is effectively improved, and the problems of poor stability and short storage period of starch glue are solved

key words: oxidized starch phosphate adhesive quick drying

corn flour adhesive is mainly used for the bonding of corrugated paper and other paper products. Historically, the adhesive used in the corrugated box industry is also looking forward to taking new steps. Because of its high alkali content and high corrosiveness to paper, the produced cartons are prone to moisture, deformation, damage and even corrosion of inner packaging goods, so it is increasingly not suitable for commercial packaging requirements. And through physics. Chemical or biochemical methods have changed the structure, physical properties and chemical properties of raw starch. A variety of modified corn starch adhesives with specific properties and uses have attracted extensive attention because of their high bonding strength, light weight, non corrosiveness, good moisture resistance, strong stiffness, good toughness and low cost

there is a common defect in the practical application of corn starch adhesive, that is, the drying speed of paperboard is slower than that of traditional bubble alkali. In view of this, in this paper, corn starch is used as raw material, potassium permanganate is used as oxidant, and acidic sodium phosphate is used as phosphoric esterification reagent to study the reaction conditions of wet preparation of oxidized starch phosphate. The stability and quick drying of starch adhesive are solved by adding driers at any time, and the influence of different conditions on the quality of adhesive is further discussed

1 experiment and principle part

1.1 oxidation and esterification principle

starch is a natural polymer with glucose as the structural unit. Under the action of oxidant, the hydroxymethyl group (CH2OH) on the glucose unit is partially oxidized to hydroxyl group (COOH), and esterification makes part of the hydroxyl group of starch combine with the ether group of phosphoric acid. Oxidation and phosphorylation reduced the number of hydroxyl groups in starch molecules, hindered molecular association, that is, weakened the binding ability of intermolecular hydrogen bonds; At the same time, it can also partially break the oxygen bridge (glycoside chain) between the basic rings of starch molecules, reduce the degree of polymerization and degrade macromolecules, thus increasing the solubility, fluidity and adhesion

1.2 selection of process methods

there are many methods of making starch adhesive, such as alkali paste method, dextrin method, esterification etherification method, oxidation method and grafting copolymerization with other polymer monomers. Among them, the adhesive made by oxidation method has strong adhesion, good stiffness after edge pasting, and the manufacturing method is relatively simple, so it is currently used more methods. Oxidation process can be divided into cold process and hot process. Cold process generally has a long production cycle, which is greatly affected by seasonal temperature, and sometimes the reaction takes ten hours. The heating method has the advantages of short production cycle, stable product quality and freedom from seasonal temperature changes. In this paper, a unique method combining thermal oxidation and phosphoric acid esterification is adopted

1.3 selection of oxidants

oxidants available for the production of starch adhesives include hydrogen peroxide, hypochlorite, chlorate, potassium permanganate or multi oxidants. We used hydrogen peroxide, oxychloride and potassium permanganate as oxidants to compare the viscosity of oxidized starch under the same conditions. The results are shown in the table:

Table 1 Relationship between oxidant and viscosity

serial number oxidant initial viscosity (s)

1 H2O2 46

2 NaClO 43

3 KMnO4 50

the amount of oxidant is 2% of starch

it can be seen from the above table that the initial viscosity of the adhesive prepared by using potassium permanganate as oxidant is the largest, but the viscosity change is not great. The three oxidants have their own characteristics. Hydrogen peroxide is used as oxidant to oxidize corn starch to produce adhesive with high adhesive strength and good storage stability; Sodium hypochlorite is a by-product of many chemical plants and its price is low; Potassium permanganate has the advantages of fast oxidation speed, good effect, small dosage and stable product quality. In particular, it has the advantages of indicating the end point of the reaction, which is easy to control production and conducive to phosphatization. Potassium permanganate is selected as oxidant in this paper

1.4 dosage of esterification agent

NaH2PO4 and Na2HPO4 with a ratio of 1:2 were selected as esterification agents. The effect of esterification agent/starch on the degree of substitution of the product was tested. With the increase of the ratio, the degree of substitution increased correspondingly. The results are shown in Table 2

but this is actually unrealistic Table 2 Relationship between esterification agent/starch and degree of substitution

esterification agent/degree of substitution of starch (D. s)

l:2.50 0.02

l:1.50 0.1

1:1.2 0.14

1:1.0 0 0.145

l:0.8 0.149

it can be seen from the above table that as the proportion of esterification agent increases, substitution the degree also increases, When the ratio of starch is reduced to 1.2, the degree of substitution changes little, and the inorganic phosphorus content of the product is correspondingly increased, which is detrimental to the quality of the product. Therefore, the ratio of esterification agent and starch is selected as 1:12

1.5 selection of other additives

1.5.1 crosslinking agent

the purpose of adding crosslinking agent is to improve the crosslinking degree and initial viscosity of adhesive. Borax can be used as crosslinking agent. Borax can form a b4o72 centered structure with hydroxyl, carbon and other oxygen-containing groups in water, which increases the viscosity and surface tension of starch adhesive, thereby improving the adhesion and water resistance. The dosage of borax can be controlled at 1 ~ 2% of starch. Excessive dosage will lead to excessive crosslinking, decreased fluidity, and even loss of viscosity; If the dosage is too small, it will not increase the viscosity

1.5.2 catalyst and drier

catalyst can accelerate oxidation reaction and reduce reaction temperature. We choose ZnO as catalyst, and the dosage is about 0.1% of the amount of starch

in order to overcome the defect of slow drying of starch adhesive, we chose the cheap and easily available bentonite as the drying promoter. It can be well dispersed in the adhesive, and the drying effect is obvious. It can be moved at will 30 minutes after sizing

1.5.3 preservative

in order to increase the storage period, we added the preservative sodium benzoate. In order to keep the adhesion unaffected and make the cost increase small, only a small amount of preservative can be added

1.6 basic formula (unit:%)

corn starch 18 bentonite 1.0 ~ 1.5

KMnO4 0.36 NaH2PO4 7 ~ 8%

concentrated H2SO4 2 Na2HPO4 7 ~ 8%

Zn0 0 0. 02~0。 1 a small amount of sodium benzoate

borax 0.3 ~ 0.7 water 70 ~ 80

1.7 product performance index measurement results (as shown in Table 3)

Table 3 product performance index

test item performance index

appearance light yellow viscous liquid

viscosity (coated with 4 cups) 20 ~ 40%

solid content about 18%

density (25 ℃) about 1.10g/cm3

stability (within 12h) 0. 95~1。 0

storage period 2 months

drying time 1~2h

stability