Development of Fast-dry Corrugated Cardboard Oxidized Starch Adhesive

【Abstract】 Starch phosphate esters were prepared by the oxidation of corn starch as raw material. Catalysts, driers and preservatives were used to prepare oxidized starch adhesives for corrugated paperboard. The drying speed is effectively improved, and the problem of poor stability and short storage period of the starch glue is solved.

Keywords: oxidized starch starch phosphate binder fast drying

Cornmeal binders are mainly used for the bonding of corrugated paper and other paper products. Historically, the adhesive used in the corrugated box industry has always been silicate. Because of its high alkali content and corrosiveness to paper, the produced cartons are susceptible to damp, deformation, damage or even corrosion of the inner packaging products. The less suitable for commercial packaging requirements. And through physics. Chemical methods or biochemical methods change the structure, physical properties and chemical properties of the original starch, and a variety of modified corn starch adhesives with specific properties and applications have high adhesive strength, light weight, no corrosion, and good moisture resistance. It has great strength, good toughness, and low cost, and it has received extensive attention.

Due to the common defect of corn starch adhesive in practical application, the paperboard is slower than the traditional scouring alkali. In view of this, using corn starch as raw material, using potassium permanganate as oxidant and acid phosphate as phosphating agent, the reaction conditions for preparing oxidized starch phosphate by wet method were studied. Starch was added to solve starch by adding driers. Adhesive stability, quick-drying and other issues, at the same time on different conditions on the quality of the adhesive for further exploration.

1 Experiment and principle

1.1 Principle of Oxidation and Esterification

Starch is a natural polymer with glucose as the structural unit. Under the action of oxidants, the hydroxymethyl group (-CH2OH) on the glucose unit is partially oxidized to thiol (-COOH), and the esterification effect makes the partial hydroxyl of starch and ether of phosphoric acid. Base combination. Oxidation and phosphorylation reduce the number of hydroxyl groups in the starch molecule and impede the association of molecules, which impairs the binding capacity of hydrogen bonds between molecules; at the same time, it can also break oxygen bridges between the base rings of starch molecules. This reduces the degree of polymerization and the degradation of macromolecules, thereby increasing solubility, fluidity, and adhesion.

1.2 Process Options

There are various methods for producing starch adhesives, such as alkaline paste method, dextrin method, esterification etherification method, oxidation method, and graft copolymerization with other polymer monomers. Among them, the adhesive produced by the oxidation method has strong adhesion, the stiffness of the cardboard after the paste is good, and the production method is relatively simple. Therefore, more methods are currently used. Oxidation is divided into cold and hot systems. The cold process generally has a long production cycle and is affected by the seasonal temperature. Sometimes the reaction takes ten hours. The thermal method has the advantages of short production cycle, stable product quality, and no limitation of seasonal temperature changes. This article uses a unique combination of thermal oxidation and phosphate esterification.

1.3 Selection of oxidants

The oxidizing agents available for the production of starch binders are hydrogen peroxide, hypochlorites, chlorates, potassium permanganate or polyhydric oxidants. We used hydrogen peroxide, oxo acid salt and potassium permanganate as oxidants to compare the viscosities of oxidized starch under the same conditions. The results are shown in the table below:

Table 1 Relationship between oxidants and viscosity

No. Oxidizer Initial Viscosity (S)
1 H2O2 46
2 NACLO 43
3 KMNO4 50
The oxidation acidity PH is 3 and the amount of oxidant used is 2% of the starch.

As can be seen from the above table, the use of potassium permanganate as an oxidant, the adhesive obtained by the initial viscosity is the largest, but the viscosity change is not great. Each of the three oxidizing agents has its own characteristics. Hydrogen peroxide is used as an oxidizing agent to oxidize corn starch. The adhesive strength is relatively large and the storage stability is good. Sodium hypochlorite is a by-product of many chemical plants, and the price is low; while the potassium permanganate oxidation rate Fast, effective, low dosage, stable product quality, especially with the advantage of indicating the end of the reaction, easy to control production, is conducive to phosphate esterification. This article uses potassium permanganate as an oxidant.

1.4 The amount of esterification agent

The 1:2 NAH2PO4 and NA2HPO4 were used as esterification agents and the effect of esterification agent/starch on the degree of substitution of the product was tested. As the ratio increased, the degree of substitution increased accordingly. The results are shown in Table 2.

Table 2 Relationship between esterification agent/starch and degree of substitution

Esterifying agent/starch degree of substitution (D.S)
l:2.5 0.02
l: 1.5 0.1
1:1.2 0.14
1:1.0 0.145
l:0.8 0.149

From the above table, it can be seen that as the proportion of esterifying agent increases, the degree of substitution also increases. When the proportion of starch is reduced to 1.2, the degree of substitution does not change much, and the inorganic phosphorus content of the product is correspondingly increased. The quality of the product is unfavorable, so the ratio of esterifying agent to starch is chosen to be 1:12.

1.5 Selection of other additives

1.5.1 Crosslinking agent

The purpose of adding a cross-linking agent is to increase the degree of cross-linking and initial tackiness of the binder, and borax can be used as a cross-linking agent. Borax in the water with hydroxyl, carbon and other oxygen-containing groups to form a B4O7 2 as a central network structure, so that the viscosity of starch adhesives and surface tension increases, thereby increasing the adhesion and water resistance. The amount of borax can be controlled at 1 to 2% of the starch. Excessive amounts can result in excessive cross-linking, reduced fluidity, and even loss of stickiness; too little of it will not increase viscosity.

1.5.2 Catalysts and Driers

The catalyst accelerates the oxidation reaction and lowers the reaction temperature. We use ZnO as a catalyst, and the amount is about 0.1% of the amount of starch.

In order to overcome the slow drying of starch binders, we chose cheap bentonite as a desiccant. It can be well dispersed in the adhesive, the effect of promoting drying is obvious, and it can be moved freely after sizing for 30 minutes.

1.5.3 Preservatives

In order to increase the shelf life, we added the preservative sodium benzoate, in order to not affect the adhesive force, and the cost can not be increased only under a small amount of preservatives.

1.6 Basic Formula (Unit: %)
Cornstarch 18 Bentonite 1.0～1.5
KmnO4 0.36 NAH2PO4 7 to 8%
Concentrated H2SO4 2 NA2HPO4 7~8%
ZN0 0. 02~0. 1 Sodium benzoate A small amount of borax 0.3 ~ 0.7 Water 70 ~ 80
1.7 Product Performance Indicator Measurement Results (as shown in Table 3)
Table 3 Product Performance Index Test Item Performance Index Appearance Light yellow viscous liquid Viscosity (coating 4 cups) 20~40%
Solid content about 18%
Density (25°C) about 1.10G/CM3
Stability (within 12h) 0. 95~1. 0
Storage period 2 months Drying time 1~2h
stability