Production Implementation Scheme for Formaldehyde-Free Additive Particleboard Based on Polyurethane System

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

Company: Wanhua Chemical Group Co., Ltd.

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

Introduction

To address the two major technical challenges in producing polyurethane adhesive particleboard on continuous flat-press lines-namely, the lack of initial tack on the board blanks and reduced production efficiency-a solution involving the addition of tackifiers and fast-curing agents was adopted. Results showed that adding tackifiers to the surface significantly improved the initial tack of the board blanks, preventing them from crumbling when dynamically passing through a 10 cm gap, without reducing the physical properties of the finished board. Furthermore, the addition of fast-curing agents effectively reduced the hot-pressing factor while maintaining board performance, thus improving production efficiency.

Research Background

Formaldehyde-free adhesives include polyurethane, soybean protein, plant starch, polyvinyl acetate, polyacrylate, etc. Polyurethane adhesives have been used in the engineered wood products industry for nearly 30 years and are currently the most mature formaldehyde-free adhesives used in engineered wood products industry. They are widely used in oriented strand board, particleboard and fiberboard [1]. Polyurethane adhesives not only do not contain formaldehyde, but also have many advantages compared with urea-formaldehyde adhesives: the boards made from them have excellent water resistance, good mechanical properties, and less stringent requirements on the species of raw materials and the moisture content of wood chips [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 wood. Therefore, the amount of adhesive used is low and the mechanical strength is high. According to the amount of adhesive used per cubic meter of particleboard, the amount of polyurethane adhesive used is only 1/6 of that used in urea-formaldehyde adhesives. The product performance improvement and environmental protection value far exceed those of urea-formaldehyde adhesives, and it has a higher added value.

Although polyurethane adhesives have many advantages, compared with urea-formaldehyde adhesives, the production of particleboard using polyurethane adhesives requires solving two problems in the production process. First, because the shavings after polyurethane adhesive application have no initial tack, the pre-pressed board blanks fall off when passing through the gap at the entrance of the continuous press, causing damage to the board blank structure and resulting in cracks and structural damage on the lower surface of the subsequent hot-pressed board [3]. In addition, due to heat transfer and chemical reaction reasons, the application of polyurethane adhesives in most production lines shows a slow curing speed and reduced production efficiency. These two problems are the key challenges that need to be solved to achieve formaldehyde-free production of particleboard.

With the deepening research on polyurethane adhesives in the industry and the exploration of formaldehyde-free particleboard production processes using polyurethane adhesives, solutions are emerging one after another, and the available additive systems are constantly being improved. Currently, many companies can provide corresponding tackifier and fast-curing agent solutions.

This article addresses the above issues by exploring 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 using polyurethane adhesives.

Test data

In summary, laboratory evaluation results show that the fast-curing agent significantly improves the curing speed of polyurethane adhesives. In actual production, manufacturers can optimize and adjust the dosage according to specific application requirements.

in conclusion

The low efficiency and small-scale production of particleboard blanks using polyurethane adhesives in continuous flat-press production lines are two major problems hindering the industrial-scale production of formaldehyde-free particleboard. The application of tackifiers and fast-curing agents in particleboard preparation demonstrates that:

1) Adding a tackifier can greatly improve the initial tack of the slab, allowing it to pass completely through the gap of the tackifier evaluation instrument without crumbling, potentially solving the problem of slab crumbling during gap filling. 2) Performance testing of slabs made with the added tackifier showed that the addition did not impair the slab's performance. 3) Using a fast-curing agent, even with a very small amount added, can effectively shorten the hot-pressing time.

Particleboard manufacturers can choose suitable tackifiers and fast-curing agents from the market according to their own needs to achieve the goal of continuous formaldehyde-free production of polyurethane adhesive particleboard. Through process optimization, they can achieve the best cost control and provide the market with green and environmentally friendly new products with better quality and lower cost.