Optimisation of a bio-based adhesive and the parameters for laboratory particleboard production
- Degree programme: BSc in Holztechnik
- Author: Liam Calvin Hilton Dorn
- Thesis advisors: Prof. Dr. Ingo Mayer, Prof. Dr. Heiko Thömen
- Year: 2023
Wood-based panels (WBP) are of great importance for the construction, furniture and packaging sectors. The adhesives for their production are largely based on components that are increasingly viewed critically due to their petrochemical origin or proven harmfulness to the environment and health - a fact also reflected in the increasing amount of research into alternative adhesive formulations that consist of biogenic and harmless components to the greatest possible extent.
Objectives and procedure outline
In the context of the thesis, a newly developed resin formulation based on Lignin and 5-Hydroxymethylfurfural (5HMF) derived from hexoses was to be investigated regarding its suitability for use as an adhesive in laboratory particleboard (PB) production. In a first phase, possibilities for optimising the formulation with regard to curing/bonding performance and processability were to be examined. The effects of the optimisation measures were assessed with differential scanning calorimetry (DSC), gelation time measurements and lap shear tests (Automated Bond Evaluations System - ABES). Prior to PB production, the process was then to be modelled with the help of a simulation software (Virtual Hot Press 2.0), which, in a previous step, had to be initialised based on the given press laboratory conditions and measured data regarding the optimised adhesive's curing behaviour. Lastly, one-layer laboratory PBs were to be produced, tested for their internal bond strength (IB) and bending behaviour and the obtained mechanical values were to be compared with the requirements specified in the corresponding standard (SN EN 310).
Key Results
The investigations enabled the qualitative and quantitative description of specific aspects in connection with the optimisation of the Lignin-5HMF resin (LHMF) as well as influencing factors in its use as an adhesive. It showed that its curing temperature is lowered with increasing addition of sodium hydroxide (NaOH) and the resulting higher pH. Regression functions were derived to describe the relation of the three parameters NaOH content, pH and curing temperature. Hexamethylene diamine (HMDA) and para-Tolouenesulfonic acid (p-TSA) were disqualified as alternative curing agents. ABES investigations on adhesive mixtures with systematically varied amounts of calcium carbonate (CC) and wheat flour (WF) were able to demonstrate their influence on the bond formation with small-sized veneer samples as well as on the adhesives' processability. Increased amount of additives delayed the strength development at pressing times of up to 10s, but after 30s no difference could be detected that could be attributed to higher content of CC and WF. With the help of a multifactorial ABES test series, data were collected for a numerical model of the hot pressing process and the conditions in the pressing laboratory were virtually modelled. The simulation’s predictions on IB and Bending Modulus of Elasticity could not be maintained in view of subsequent PB productions and corresponding mechanical tests. With the variation of different process parameters for PB production and methodically adapted ABES investigations, different factors were examined with regard to their influence on bond strength and strength development, with the result that the moisture content must be assumed to be the most detrimental factor. A final investigation on PBs, whose mat moisture content was reduced to a minimum by varying the adhesive formulation, was able to support this assumption. With a formulation adjusted to the lowest still processable moisture content, laboratory PBs could be produced that meet the requirements in terms of IB as specified in SN EN 310 for the most widely used PB type P2.
