What are the advantages of using adhesives for straw boards with silica sol as the main colloid?

The content is excerpted from "Research on the Preparation and Application of Inorganic Environmentally Friendly Adhesives for Straw-Based Boards" published in the 6th issue of the journal "Forest Products Industry" in 2018.

Authors: Liu Zhen, Ma Lei, Nie Ning, et al.

my country is a major agricultural country with abundant straw resources. Experts estimate that my country's annual crop straw production is 700 million tons, accounting for approximately 30% of the world's total straw production. Currently, the effective utilization rate of crop straw is only 30%. Crop straw contains abundant cellulose, which can be used as a raw material for engineered wood products. Given the current scarcity of timber resources, developing the crop straw engineered wood product industry not only transforms agricultural waste into valuable resources and conserves timber, but also yields significant economic and social benefits.

Commonly Used Adhesives Analysis

The production of engineered wood products from straw typically requires the use of adhesives and specific manufacturing processes. Adhesives are the core of straw-based panel production, determining the performance of the resulting panels. Commonly used adhesives include urea-formaldehyde resin adhesives, isocyanates, and plant protein adhesives. Urea-formaldehyde resin adhesives, being formaldehyde-based, are relatively inexpensive, but their adhesion to straw is poor, resulting in lower strength panels. Furthermore, the free formaldehyde released during straw panel production and use can pose significant health risks. Isocyanates are a high-quality adhesive with low toxicity, but their limited raw material sources, complex synthesis processes, and high cost lead to high bonding costs. These panels also present technical challenges such as flammability, moisture absorption, and high energy consumption during the molding process. Plant protein adhesives offer advantages such as abundant raw material sources, low price, and non-toxicity, but their poor water resistance fails to meet production requirements. To solve these problems, it is urgent to develop an environmentally friendly adhesive for straw boards that integrates pollution-free, high strength, strong water resistance, and thermal insulation properties, while also being inexpensive and having low energy consumption in board production.

New type of inorganic environmentally friendly adhesive

This paper develops an inorganic, environmentally friendly adhesive with silica sol (mSiO2·nH2O) as the main colloid and aluminum chloride (AlCl3), aluminum oxide (Al2O3), magnesium oxide (MgO), zinc oxide (ZnO), and aluminum hydroxide [Al(OH)3] as fillers, and applies it to the manufacture of straw-based boards. The effects of the moisture content, density, compressive strength, flexural strength, 24-hour water absorption thickness swelling rate, and uniform temperature burning performance of the manufactured boards were investigated.

Adhesive formulation

Extensive preliminary experiments have shown that the amounts of AlCl3, Al2O3, MgO, ZnO, and Al(OH)3 in the adhesive significantly affect the properties of the manufactured boards. By varying the amounts of AlCl3, Al2O3, MgO, ZnO, and Al(OH)3 in the adhesive, this study tested the moisture content, density, compressive strength, flexural strength, 24-hour water absorption thickness swelling rate, and uniform temperature burning performance of the pressed boards. A single-factor experimental method was used to determine the formulation for preparing the inorganic environmentally friendly adhesive.

in conclusion

An inorganic environmentally friendly adhesive for strawboard was prepared using silica sol (mSiO2·nH2O) as the main colloid and aluminum chloride (AlCl3), aluminum oxide (Al2O3), magnesium oxide (MgO), zinc oxide (ZnO), and aluminum hydroxide [Al(OH)3] as fillers. The optimal formulation of the inorganic environmentally friendly adhesive was determined by testing the performance of the pressed boards. The percentages of each filler in the formulation relative to silica sol were: AlCl3 6%, Al2O3 2%, MgO 6%, ZnO 2%, and Al(OH)3 2%, with an optimal mass ratio of adhesive to straw of 1.0.

The performance indicators of the pressed boards under the optimal adhesive formulation and adhesive/straw mass ratio are as follows: moisture content 4.53%, density 888.56 kg/m3, flexural strength 3.56 MPa, compressive strength 3.59 MPa, thermal conductivity 0.13 W/(m·k), 24-hour water absorption thickness expansion rate 2.25%, and uniform temperature burning performance 4.53%. All relevant indicators are equal to or better than the enterprise standards of similar products.