Production implementation plan for polyurethane system formaldehyde-free particleboard

Authors: Gong Cheng, Tu Song, Yuan Min, Xin Bo, Jin Yanli

Unit: Wanhua Chemical Group Co., Ltd.

Source: China Wood-Based Panels, Issue 7, 2018

Introduction

To address the two major technical challenges of producing polyurethane adhesive particleboard on a continuous flat-bed press line-the lack of initial tack and reduced production efficiency-a solution was developed by adding a tackifier and a fast-curing agent. Results showed that the addition of a surface tackifier significantly improved the initial tack of the slab, allowing the slab to dynamically pass through a 10 cm gap without breaking apart, and that the addition of the tackifier did not degrade the physical properties of the finished board. Furthermore, the addition of a fast-curing agent effectively reduced the hot-pressing factor while maintaining board performance, thereby improving production efficiency.

Background

Formaldehyde-free adhesives include polyurethane, soy protein, plant starch, polyvinyl acetate, polyacrylate, etc. Polyurethane adhesives have been used in the wood-based panel industry for nearly 30 years and are currently the most mature formaldehyde-free adhesives in the wood-based panel industry. They are widely used in oriented strand board, particle board and fiber board [1]. Polyurethane adhesives not only do not contain formaldehyde, but also have many advantages over urea-formaldehyde adhesives: the boards produced have excellent water resistance, good mechanical properties, and are less demanding on the moisture content of raw material tree species and wood particles [2]. The bonding principle of polyurethane adhesives is different from that of urea-formaldehyde adhesives. It is a chemical reaction between the NCO groups in the adhesive and the hydroxyl groups in the chemical components of the wood. Therefore, the amount of adhesive applied is low and the mechanical strength is high. Calculated by the amount of adhesive used per cubic meter of particle board, the amount of polyurethane adhesive used is only 1/6 of the amount used for urea-formaldehyde adhesive. The product performance improvement and environmental value far exceed those of urea-formaldehyde adhesive products, and it has a higher added value.

Although boards made with polyurethane adhesives have many advantages, compared with urea-formaldehyde adhesives, the production process of particleboards using polyurethane adhesives requires solving two problems. First, because the particles after polyurethane adhesive application have no initial adhesion, the pre-pressed slabs fall off when passing through the gap at the entrance of the continuous press, destroying the slab structure and causing cracks and structural damage on the lower surface of the subsequent hot-pressed boards [3]. In addition, due to heat transfer and chemical reactions, the application of polyurethane adhesives on most production lines shows slow curing speed and reduced production efficiency. These two problems are key difficulties that need to be solved to achieve formaldehyde-free production of particleboards.

With the deepening of research on polyurethane adhesives in the industry and the exploration of the production process of formaldehyde-free particleboard with polyurethane adhesives, solutions are emerging in an endless stream and the available auxiliary agent systems are constantly being improved. Currently, many companies can provide corresponding tackifier and fast curing agent solutions.

In response to the above problems, this paper explores the application of two additives, tackifiers and fast curing agents, to solve the problems of "loose blanks" and "low efficiency" in the production of formaldehyde-free particleboard with polyurethane adhesives.

Test data

In summary, laboratory evaluation results show that fast-curing agents significantly improve the cure speed of polyurethane adhesives. In actual production, manufacturers can optimize and adjust the dosage based on specific application conditions.

in conclusion

The looseness and low efficiency of particleboard produced by continuous flat-press production lines using polyurethane adhesives are two major problems in achieving industrial production of formaldehyde-free particleboard. The use of tackifiers and fast curing agents in particleboard preparation shows that:

1) Adding a tackifier significantly improves the initial tack of the slab, allowing it to pass through the gap of the initial tackifier evaluation instrument without breaking apart, potentially resolving the problem of slab breaking apart during the gap. 2) Performance testing of panels produced with the addition of the tackifier showed that the addition of the tackifier did not compromise the performance of the panels. 3) Using a fast-curing agent, even at minimal addition, can effectively shorten the hot pressing time.

Particleboard manufacturers can choose appropriate tackifiers and fast curing agent products on the market according to their own needs to achieve the goal of continuous formaldehyde-free production of polyurethane adhesive particleboard, and achieve optimal cost control through process optimization, providing the market with new green and environmentally friendly products with better quality and lower cost.