## 1 Introduction  
Particleboards produced from raw wood material are highly affected by the properties of the wood. It has been reported in the literature that changes in the raw material caused by the storage time, age of tree, location in stem, and origin may have a strong impact on its chemical properties, and, subsequently, on the mechanical and physical properties of wood-based materials [1; 2; 3; 4]. These phenomena impose adjusting conditions on the process, especially in terms of the adhesive used and the amount of hardener.  
The chemical properties of wood and wood extractives, such as pH value and buffering capacity, are considered prime factors in bonding [5]. The gel time of a urea-formaldehyde (UF) resin strongly depends on the acidity of the wood substrate which is associated with the content of the wood extractives [6; 7]. The buffering capacity of a material is the sum of the buffering capacities of each individual acidic and basic component and the effect of the interactions among them [8].  
Buffering capacity (\(\beta\)) is defined as  
\[\beta=\frac{n_{acid}}{\Delta pH}, \tag{1}\]  
where \(n_{acid}\) is the number of acid moles that caused a change in the pH of a solution, expressed as \(\Delta pH\).  
The buffering capacity value can be applied to woody material used in, for example, the particleboard industry. This can be the simplest and most accurate approach to describe the influence of a raw material on the adhesive gelation process without the need for deep insight into the chemical properties or the origin of the feedstock. As a result, it is possible to find the most accurate amount of hardener so that the effects of the basic or acidic components of the wood are balanced. A commonly used methodology is based on the extraction of chips in boiling water and titration with acid solution or titration of the acetic acid liberated from the wood [9; 10]. Most common protocols found in the literature are based on the titration of wood aqueous extracts to the end point at pH 3 [11; 12] or pH 4 [13]. These values are the pH at the gel point for UF resins. However, it has been recently proved that such a protocol for the determination of the acid buffering capacity of wood material is not reliable [14]--not all compounds present in wood are soluble in hot water [15], although they still have an influence on the adhesive gelation process. This leads to the hypothesis that the buffering capacity determination cannot be based on the titration of wood extractives but must include the titration of a woody material suspension (chips or fibers). Several aspects investigated in a previous study revealed that the presence of lignocellulosic material in a titrated system was crucial [14]. More recently, another alternative approach to determine the ABC of woody material has been proposed [16]. A simplified method with a pre-acidification step has been shown to be more resistant to the influence of the measurement conditions and the operator.  
Thus, the main aim of the present study was to compare three different methodologies for the determination of the acid buffering capacity (ABC) in the presence of woody material in the form of chips and to evaluate which one best describes the true acid buffering capacity of the wood. The obtained ABC values were correlated with the internal bond of particleboards, so that a protocol providing the most reliable results could be indicated.  
In this paper, different methods of measuring acid buffering capacity were examined. Basic statistical methods, including linear regression and root-mean-square error (RMSE), were used to build and compare the models. Three materials of very different chemical characteristics were chosen for the experiments--oak, pine, and ammonia-treated oak.