Formaldehyde Use and Alternative Biobased Binders for Particleboard Formulation: A Review

Stephen Warui Kariuki,Jackson Wachira,Millien Kawira,Genson Murithi

doi:10.1155/2019/5256897

Abstract

Formaldehyde-based resins are conventionally used as a binder in formulation of particleboard. Epidemiologic studies have shown that formaldehyde is carcinogenic. Efforts to reduce the health hazard effects of the fomaldehyde-based resin in the particleboard formulation have included use of scavengers for formaldehydes and use of an alternative binder. Use of scavengers for the formaldehyde increases the cost and maintenance of particleboard formulation. There is no proof that scavengers eliminate the emission of formaldehyde from particleboard. Use of biobased binders in particleboard formulation provides an alternative for eliminating use of the formaldehyde-based resin. However, the alternative is hindered by challenges, which include limitations of physical and mechanical properties. The challenge has continuously been acted upon through research. The paper presents an overview of the use of starch as an alternative binder. Improvement over time of the starch and limitations thereof requires to be addressed. Use of the modified starch has shown increased particleboard performance. Mechanical strength, such as modulus of rupture, modulus of elasticity, and internal bonding in particleboards, however, remains to be a challenge.

Highlights

IntroductionSelamat et al [46] compared physical and mechanical properties of particleboard formulated from rubberwood with urea formaldehydes and native starch, separately as binders
Starch modified with other chemicals is used as a substitute for formaldehyde-based resin in particleboard formulations
Hydroxyl group modification in starch is achieved through the introduction of alkyl groups or oxidation to carboxylic acid. is reduces the hydroxyl functional groups that determine the water absorption and thickness swelling which in turn affect the mechanical properties of particleboard

Summary

Introduction

Selamat et al [46] compared physical and mechanical properties of particleboard formulated from rubberwood with urea formaldehydes and native starch, separately as binders. High water absorption of particleboard formulated with the carboxymethyl starch may be attributed to the presence of hydroxyl groups. Imam et al [65] cross-linked corn starch with polyvinyl alcohol (PVOH) using hexamethoxy methylmelamine (HMMM) to bond lignocellulose materials together in an acidic medium Under this condition, methoxy groups from HMMM reacted with the hydroxyl group from starch in the presence of PVOH to form ether bond [65], as in Scheme 1. Researchers worked with different particle sizes and found that the starch-based adhesive gave comparatively better physical and mechanical properties. Scheme 1: Schematic chemical crosslinking reaction [65]

H HO H H

H H n Starch-based polyurethane n

Findings

Conclusion