Surface Checks Research Articles

Moisture changes and surface checking development during drying of Masson pine wood

Deformation and surface-checking defects in wood are closely related to the drying stress caused by shrinkage and moisture content (MC) gradients throughout the drying process. In this study, 50-mm-thick Masson pine (Pinus massoniana Lamb.) lumber was used as the research object. The drying stress caused by shrinkage behavior and MC changes was monitored, and the development of surface checks was observed during the drying process. Results showed that when the average MC was 60%, the free water in the surface layer of lumber evaporated completely, causing the MC to decrease below the fiber saturation point (FSP). The surface layer was subjected to tension stresses, resulting in surface checks which primarily distributed in the latewood area and propagated longitudinally. When the average MC was between 30% and 40%, the combined effects of the high MC gradient and anisotropic shrinkage of the wood resulted in further expansion of the checks. As the average MC decreased to less than 20%, the MC of the core layer lumber decreased below the FSP, resulting in the closure or even disappearance of most surface checks. The critical point (average MC of 60%) of drying stress was obtained, which can benefit the fine-tuning of kiln-drying schedules and improve the drying quality of Masson pine wood.

Internal stress development within wood during drying: A master curve concept and its application on drying stress evaluation

The generation of internal stress (IS) in flat-sawn and quarter-sawn rubberwood boards during drying has been investigated using an online restoring force (RF) technique, which restrained a half-split rectangular wood specimen. Particular attention was given to the longest IS reversal regime. The IS development proceeds faster in the flat-sawn specimens than that in the quarter-sawn specimens while the maximum IS magnitudes in both specimens are rather similar. By normalizing the IS reversal period, a master IS profile, the derivative of the measured RF to the IS reversal time ratio versus the IS reversal time ratio, is proposed. This master curve, exhibiting some degree of independence from wood orientation and drying temperature, shows variations correlated with the free water content in the wet zone and the dry/wet zone fractions. The process of IS reversal, unaffected by temporary unrestraint, advances as the dry zone expands inwards and ends when the wet zone disappears. Assuming mechanical equilibrium between the dry and wet zones, the IS in both zones can be estimated from the RF data. The maximum tensile IS in the dry zone, indicating a risk of surface checks, evolves at slightly lower magnitudes at higher drying temperatures and is lower in the quarter-sawn specimens. The IS relaxation in the dry zone, still largely taking place in the absence of the applied RF, highlights the main contribution of the dry/wet zone fractions, continuing to proceed without restraining, to the IS development. These findings, emphasizing the significance of dry and wet zones, should pave the way for a better understanding of the IS development within wood during drying.

Measurement of surface-checking in sliced lamellae-based engineered wood flooring using digital image correlation

The lack of quantitative methods for surface-checking measurements may hinder improving the product characteristics of engineered wood flooring products built with sliced top-layer lamellae. This study evaluated the digital image correlation method for its applicability to surface checking measurements in engineered wood flooring elements with the top-layer comprising the plain sliced lamellae of oak (Quercus spp.) species with nominal thicknesses of 1.5–4.5 mm. The method involves observing full-field surface displacements of the sliced lamellae-based wood flooring specimens subjected to an accelerated sorption/desorption cycle. Detection of surface checks relates to discontinuities in surface displacements which can be interpreted from the output strain data as strain peak regions. Additionally, a surface-checking index was defined to describe the extension of surface-checking. Exposure tests were performed on a combination of coating presence and a different number of testing cycles. The main findings provide insight into the method procedure parameters, such as exposure duration, climate conditions, analysis parameters and recommendations regarding the digital image correlation setup settings and specimen manufacturing.

Temporal changes in strain condition on all lateral surfaces during pretreatment before timber drying

Wood drying, such as boxed-heart square timber, often involves surface checks, which spoils the appearance of wood products and reduces their market value. Pretreatments are performed to avoid the surface checks, but detailed information about surface strain during timber drying remains unclear. In this study, surface strain detections were performed using two types of strain sensors (strain gauge and optical fiber strain sensor) to understand the surface dimensional changes during a series of pretreatments, consisting of steaming and high temperature and low humidity treatment. Simultaneous strain measurements based on the optical fiber sensor grasped the surface strain distributions in each lateral surface during timber drying; contraction behaviors were observed in the middle part of most surfaces in the early steaming stage, while one surface showed expansion. A remarkable expansion was detected in one surface during the high temperature and low humidity treatment, although most of the other surfaces showed gradual contraction behaviors. It was also discovered that the above detected behaviors were gradually reduced with the progress of each pretreatment.

Within-species variations in drying and preservative intake properties: a case of two progenies of plantation grown Melia Dubia CAV

Two progenies of 7 years old plantation grown Melia dubia Cav. were taken for carrying out studies on variability in drying and preservative intake properties. Terazava1 method of testing drying properties was used to give scores to various drying defects occurred in two progenies. The preservative intake properties like retention, penetration, treatability etc were determined using standard methods. Results indicate that the drying properties varied from progeny to progeny. Occurrence of the defects like surface checks were found to vary progeny to progeny, whereas, defects like surface deformation and honey combing didn’t vary. Variation in preservative properties like retention and treatability was found to vary. The study indicates that M. dubia species may possess considerable intra-species variation in drying and preservative intake properties in the plantations of seed origin.

The formation mechanism of microcracks and fracture morphology of wood during drying

The surface checks or internal cracks from drying could significantly affect the processing and utilization of the wood. Therefore, it is of great significance to investigate the formation mechanism of cracks and reduce its occurrence. In this work, the development of cracking was quantified and its relationship with moisture content (MC) gradient and anisotropic shrinkage was analyzed. Results showed that the slight shrinkage occurred at the MC of 40%, and the shrinkage ratio at the end of drying was about 7.38% in the tangential (T) direction and 4.35% in the radial (R) direction. The shrinkage ratio of T/R in the MC range of 30%–15% was about 1.8, which was higher than that (1.65) in the MC range of 15%–5%. Cracks initiation was observed at average MC of 45%. The area and number of cracks reached a maximum at 15% MC. During the late stage of drying, the drying stress of the surface layer was reversed from tensile to compressive, which leads to the narrowing or closure of the cracks. Moreover, the fracture morphology of wood cells was observed at the microscopic level, indicating that the failure firstly occurred in the intercellular layer between the ray tissue and the tracheid in the latewood. The ray cells presented intact, and the lamellar structure between ray tissues and between the ray cells and the tracheids were the weak points of wood during drying. The results would contribute to keeping in minimum drying defects and improving the drying quality of wood.

Influence of check depth, redrying conditions of various ambient humidities, and the presence or absence of airflow on moisture trapping in surface checks of wood

Influence of check depth, redrying conditions of various ambient humidities, and the presence or absence of airflow on moisture trapping in surface checks of wood

Effects of pre-steaming treatment on high-temperature and low-humidity drying characteristics of super-heavy timber with boxed-heart of Korean red pine and Douglas-fir

This study aimed to investigate how pre-steaming affects the drying times, final moisture contents (final MCs), and prevention of checking during the high-temperature and low-humidity drying process of boxed-heartwood Korean red pine (Pinus densiflora S. et Z.) and Douglas-fir (Pseudotsuga menziesii) with 20 × 20 cm and with 30 × 30 cm cross sections. Although average final MCs of the larger cross sections were slightly higher than those of smaller cross sections, all were over-dried between 3.3% and 8.1% MC, compared to the in-use moisture content for outdoor building materials. All the pre-steamed samples were only slightly defected by surface checks of 5 mm or less in width. The sample timbers with the 20 × 20 cm cross-sectional size were slightly defected by internal checking, whereas those with the 30 × 30 cm cross-sectional size were severely defected. However, there was no clear impact of pre-steaming time on the prevention of internal checking.

Corrective Interventions to End-Splitting and Surface Cracking in Kenya Grown <i>Eucalyptus grandis</i> Poles

This study determined the effect of three pole pre-drying handling techniques, on end-splitting and surface checking in Eucalyptus grandis poles from highland and low land areas in Kenya. A total of 144 Eucalyptus grandis trees were sampled from two sites; Kericho, representing the wet highlands and Londiani representing the drier lowlands regions of Kenya. Pole samples from both sites were subjected to the three pre-drying handling techniques for the first 30 days after felling and allowed to dry to the required moisture level under observations. The number of end splits and surface checks on each sample pole were counted and the length of the worst ones was measured in millimeters after every 15 days until all the poles reached 25% MC. The sap wood and heart wood ratios were determined from selected samples. Results showed that on the overall, poles from high land areas had the highest sapwood proportions and similarly had the highest number and the longest end splitting and surface checks. On the other hand, pre-drying techniques that allowed felled trees to dry slowly with their foliage intact for the first 30 days of felling produced the best quality poles, with fewer and shallower end splits and surface checks. The study recommended that felling and leaving poles to dry slowly with foliage intact be considered in reducing losses incurred as a result of wood stresses during drying of poles.

Corrosion Inhibition of Carbon Steel in 2.0M HCl Solution Using Novel Extract (Pulicaria undulate)

Plant Pulicaria undulate (PU) extract is examined as a corrosion inhibitor for carbon steel (CS) dipped in 2.0M HCl. The study was conducted utilizing ac impedance spectroscopy (EIS), Mass loss (ML), polarization (PDP) tests, and surface checks were utilized to illustrate the importance of this PU extract to prevent the corrosion process for CS. The influence of temperature and concentration of PU on the efficacy of inhibition were tested. The corrosion mechanism occurs when the PU extract molecules block the active center in the electrode surface. Langmuir isotherm is the isotherm that is applied in the process of adsorption. The effect of temperature at various temperatures on the corrosion efficacy was investigated in case of the presence and absence of the extract. Finally, thermodynamic parameters for the activation and adsorption processes were determined. Results of all methods used were in good agreement.

Machine learning-based prediction of surface checks and bending properties in weathered thermally modified timber

Machine learning (ML)-based models, decision tree and ANFIS, were used to predict the degree of surface checking and bending properties of 30-month weathered thermally modified timber. The results showed that the investigated initial board properties did not allow accurate predictions of surface checks. ML regression and clustering analysis confirmed important variables for accurate predictions of bending properties were dynamic stiffness, acoustic velocity, density and lowest local bending modulus. ML models performed better than conventional regression models used for timber grading, and a prediction accuracy of 80–90% for bending stiffness and 50–70% for bending strength could be achieved.

Effects of knife-incising and longitudinal kerfing pretreatments on high-temperature drying of red pine and pitch pine timbers

Effects of knife-incising and longitudinal kerfing pretreatments were analyzed relative to the high-temperature drying of red pine and pitch pine timbers with cross-sections less than 15 cm. Specimens were prepared as round and square timbers with thicknesses of 9, 12, and 15 cm. They were divided into four groups: control, longitudinal kerf, knife-incised, and a combination of knife-incised and longitudinal kerf. Some results from this study, such as commercial availability and application methods of drying schedules, have immense commercial importance. The incising and kerfing treatment can be used not only to improve drying quality but also as a tool for deriving an optimal drying schedule. The kerfing treatment noticeably reduced the surface checks in square timber. However, the incising treatment caused a phenomenon in which the incisions connect to each other and develop into surface checks. The wood characteristics, such as species, type, thickness, and initial MC, had more influence on determining the drying defects than the pretreatments. For the commercial use of the drying schedule used in this study, it can be useful to determine the appropriate drying time in the third step according to the species, thickness, and shape.

Eco-Friendly Approach to Corrosion Inhibition of Copper in HNO3 Solution by the Expired Tylosin Drug

Expired Tylosin Drug (ETD) is examined as corrosion inhibitor for copper (Cu) dipped in 2.0 M HNO3. The study was conducted utilizing ac impedance spectroscopy (EIS), weight loss (WL), polarization, and surface checks to illustrate the importance of this ETD to prevent the corrosion process for Cu. The influence of temperature and concentration of ETD on the efficiency of inhibition were tested. The corrosion mechanism occurs when the ETD molecules block the active center in the electrode surface. Langmuir isotherm is the isotherm that is applied in the process of adsorption. The effect of temperature at various temperatures on the corrosion efficiency was investigated in case of the presence and absence of ETD. Finally, thermodynamic parameters for the inhibition process were determined. Results were of all methods used are in good agreement.

Inhibition of Copper Corrosion by Rice Straw Extract in 2M Solution of Nitric Acid

In our research, the rice straw extract was utilized as an eco-friendly green inhibitor to prevent Cu dissolution in 2 M of HNO3. Mass loss, electrochemical tests, and surface checks were utilized to demonstrate the importance of this green extract to prevent the Cu corrosion procedure. From all tests, one can find that with increasing the dose of rice straw extract (up to 300 ppm), the protection efficacy increased to 96.8% at 25°C. Polarization curves showed that rice straw extract is a mixed-kind inhibitor that retards the anodic and cathodic reactions. From the EIS examination, the double-layer capacitance lowered by improving the dose of rice straw extract was noticed. On the other hand, the charge transfer resistance was improved. The corrosion protection (% I) of Cu occurs by the adsorption procedure, and this metal is followed by the Flory-Huggins and Langmuir adsorption isotherms. From both isotherms, the adsorption parameters were deduced. This test was also applied at different temperatures, and the activated parameters were determined and discussed. Results gotten from all used tests are in excellent harmony.

Niclosamide and dichlorphenamide: new and effective corrosion inhibitors for carbon steel in 1M HCl solution

This research demonstrates the effect of some amide compounds (1 and 2) as corrosion inhibitors on C-steel in 1.0 M of hydrochloric solutions utilizing mass reduction studies, electrochemical [potentiodynamic (PP), AC impedance measurements (EIS), electrochemical frequency modulation] techniques, and surface checks were used to illustrate the importance of amide compounds to the corrosion protection process of C-steel. The tests displayed that the inhibition efficiency (IE%) augmented with increase in amide dose but reduced with growth of temperature. The highest inhibition efficiency is 99% for compound (1) and 98.8% for compound (2) at maximum dose tested (50 µM) by polarization method. PP data show that these compounds affect both cathodic and anodic processes (i.e. mixed type) and were adsorption on the carbon steel obeying Langmuir adsorption isotherm. The EIS results indicate that the changes in impedance parameters are related to the adsorption of amides on the alloy surface. Scanning of electron microscopy, energy transmitted X-ray—Atomic force microscopy studied the morphology of inhibited C-steel.Graphic abstract

Drying performance, as well as physical and flexural properties of oil palm wood dried via the super-fast drying method

Effects of incising parameters were studied relative to the drying performance and properties of super–fast dried oil palm wood. Different incising depths (1/3, 1/2, 2/3, and 100% of the total thickness) and distance (38 mm and 50 mm) were made on the oil palm wood boards prior to the super-fast drying procedure. All the boards achieved the desired moisture content after drying. Drying defects were minimal, as only two boards indicated end checks and surface checks defects. The board density ranged from 0.44 g/m3 to 0.60 g/m3, and the thickness swelling and water absorption of the boards ranged from 8.3% to 12.5% and 45% to 67%, respectively. The specific modulus of rupture and elasticty ranged from 0.35 N m3/kg mm2 to 0.77 N m3/kg mm2 and from 77.64 N m3/kg mm2 to 118.40 N m3/kg mm2, respectively. It can be concluded that the hole distances did not exert significant effect on the properties, with exception of specific modulus of elasticity. A hole depth of 1/3 mm was preferable, since the surface looked like no incision had been made and the sample had good physical and flexural properties.

Conocarpus Erectus Extract as an Eco-Friendly Corrosion Inhibitor for Aluminum in Hydrochloric Acid Solution

Conocarpus Erectus extract was examined as a green corrosion inhibitor for Al in 1 M HCl and evaluated by different methods (chemical & electrochemical methods). Surface checks were used to illustrate the importance of this green extract to Al's corrosion inhibition process. The inhibition efficiency (%IE) increased with the raising of both Conocarpus Erectus extract dose and temperature, indicating that this extract was adsorbed chemically on Al surface. The %IE was 91.1% when the concentration Conocarpus Erectus extract was 300 ppm. Conocarpus Erectus extract inhibits both anodic and cathodic reactions, so it is a mixed kind inhibitor. The %IE of Al occurs by the adsorption process, and this metal is subject to the adsorption, according to Temkin isotherm. The surface examination was detected by utilizing a scanning electron microscope (SEM). The outcome data obtained from all experimental studies are excellent and proved the effectiveness of Conocarpus Erectus extract for Al's corrosion resistance.

Characteristics of radio-frequency/vacuum combined with mechanical press drying of heavy softwood timbers with longitudinal kerf

Abstract The aim of this study was to evaluate the characteristics of radio-frequency/vacuum combined with mechanical press (RF/VP) drying on three softwood timbers (Douglas fir, Hemlock, and Radiata pine) with longitudinal kerfs. The results were as follows: Due to the dielectric permittivity of wood, RF/VP drying at a fixed frequency of 13.56 MHz significantly influenced the moisture content (MC) distribution, the number of surface checks, shrinkage, and warp. These observations were attributed to the formation of a temperature gradient along the charge plate during the drying. The presence or absence of pith, more affected an occurrence of surface checks than that of the stresses within the wood during drying. The longitudinal kerf reduced the number of surface checks, but did not affect the MC distribution or the twist after drying.

Performance of Thermally Modified Spruce Timber in Outdoor Above-Ground Conditions: Checking, Dynamic Stiffness and Static Bending Properties

Previous studies have shown that thermally modified wood (TMW) performs well in outdoor, above-ground conditions in terms of resistance to wood-decaying fungi. Yet, little is known about the development of defects such as checks and the corresponding mechanical properties of TMW in this condition. This experiment focused on the effect of 30 months outdoor above-ground exposure (weathering) on the degree of checking, dynamic stiffness and static bending properties of thermally modified timber (TMT) of Norway spruce. Two board pairs per log were cut from 190 logs; one board of each pair was thermally modified and the other used as control. Then, 90 board pairs were exposed to the weather in south Sweden. Surface checking and axial stiffness were monitored at six-month intervals by using digital photography and non-destructive tests (time-of-flight and resonance method) to monitor changes in the material upon weathering. Finally, all boards were tested destructively in a 4-point static bending test following EN 408 standard. Results showed that weathering had no significance influence on static bending properties of TMT even though the degree of checking was considerably higher in TMT than unmodified timber after weathering. In particular, checks along growth rings were deeper, longer and more common in TMT after weathering, especially on the pith side of boards. The maximum depth of these checks did not depend on board orientation (i.e., which side was exposed) and exceeded limits given in strength grading standards for 7% of the modified boards included. Axial dynamic stiffness determined at 6-month intervals was less influenced by fluctuations in moisture content for TMT compared to unmodified timber, but did not confirm the increase in the degree of checking of TMT. The presence of checks from weathering did influence failure modes in TMT; horizontal shear failure became more frequent and some boards failed in compression.

Radio frequency vacuum drying of Eucalyptus nitens juvenile wood

Wood drying is an important process for adding value and manufacturing innovative products. Eucalyptus nitens wood is inherently difficult to dry because of its natural propensity for checking as well as collapse and shrinkage. Lumber recovery after industrial drying of eucalypts is also very low. This study measured the wood quality of E. nitens juvenile wood (13 mm thickness) after radio-frequency vacuum (RFV) drying and wood dried in a conventional kiln dryer (KD). Drying cycles were performed using a radio frequency vacuum dryer with a 3 m3 of capacity and convective kiln-dryer equipment with a 3.5 m3 of capacity. The results showed that the drying time using the radio frequency vacuum method was reduced by 47% when compared to conventional kiln drying. The shrinkage was significantly lower in the RFV than in the conventional KD. The volumetric collapse decreased by approximately 60% in the RFV drying. RFV drying of E. nitens juvenile wood improves the wood quality for solid wood products because the intensity of surface checking and collapse are reduced.