Hygromorphic Response Dynamics of 3D-Printed Wood-PLA Composite Bilayer Actuators

The use of wood particles in wood-plastic composites (WPC) is well known and similar use could occur in materials for fused deposition modeling (FDM) 3D printing. Wood particles could be one of the possible solutions in the search for natural-based materials to minimize the use of synthetic-origin materials in additive manufacturing. Wood particles for 3D printing filaments can be made from wood waste and could serve as a cheap filler or as a value-added reinforcing component, depending on their properties and incorporation. The disadvantages of wood (dimensional changes due to water adsorption and desorption) could be used as functions when dimensional change is desirable, such as in shape-changing 4D printing materials. In this research, FDM printing materials made of polylactic acid (PLA), with different amounts of wood particles, were used to design moisture-induced shape-changing bilayer actuators, which could serve as a principle for active façade or ventilation valves. The initial research shows that the wood content in the WPC causes dimensional changes and thus shape changes of the designed actuators under changing climates. The shape change depends on the ratio of the materials in the two-layered actuator and the wood content in the wood-PLA composite used, and thus on sorption. The rate of the shape change behaves in the same way: the higher the wood content, the greater the change observed. The dynamics of the hygromorphism of bimaterial composites is greater with a small amount of added hygromechanically active material.

Comparison of different approaches to estimate bark volume of industrial wood at disc and log scale

Within the wood supply chain, the measurement of roundwood plays a key role due to its high economic impact. While wood industry mainly processes the solid wood, the bark mostly remains as an industrial by-product. In Central Europe, it is common that the wood is sold over bark but that the price is calculated on a timber volume under bark. However, logs are often measured as stacks and, thus, the volume includes not only the solid wood content but also the bark portion. Mostly, the deduction factors used to estimate the solid wood content are based on bark thickness. The aim of this study was to compare the estimation of bark volume from scaling formulae with the real bark volume, obtained by xylometric technique. Moreover, the measurements were performed using logs under practice conditions and using discs under laboratory conditions. The mean bark volume was 6.9 dm3 and 26.4 cm3 for the Norway spruce logs and the Scots pine discs respectively. Whereas the results showed good performances regarding the root mean square error, the coefficient of determination (R2) and the mean absolute error for the volume estimation of the total volume of discs and logs (over bark), the performances were much lower for the bark volume estimations only.

Influence of aggressive media on the relaxation properties of wood-polymer composites

Measurements of stress relaxation of two samples of decking boards after exposure in rain and chlorinated water, in ice, and in a mixture of gasoline and water in different concentrations from 1 to 7% were carried out. Samples consisting of 60% wood flour, 30% polyvinyl chloride and 10% additives were used for measurements. Additives are flame retardants, stabilizers, modifiers and dyes. The mineral filler CaCO3 was used as modifier. In sample No.1, the CaCO3 content was 42% and the wood content was 18%. For sample No.2, the CaCO3 content was 24% and the wood content was 36%. As a result of measurements after exposure for 200 days, it was found that the relative drop in mechanical stress decreases when the mineral filler is added to the composition. The nonlinear mechanical behavior for the initial sample No.1 is observed at 2% strain, and for the sample No.2 – at 3% strain. When aged in chlorinated water and in ice, the nonlinear mechanical behavior is observed for all deformations. The generalized relaxation curves indicate that decking boards can be used with confidence for a long time.

3D-Simulation of Wood Stacks to Analyze the Influence of Log Properties on Stack Volume

The quantification of the solid wood content in a wood stack has been an object of investigation since the 18th century. Particularly, the log parameters exert a considerable influence on the volume of the stack, such as (1) the log midpoint diameter, (2) average bark thickness, (3) crookedness, and (4) log taper. Although many of these parameters have already been studied and some are already considered in many countries when measuring wood stacks, their influence has not been analyzed individually so far since a broad statistical database is needed and the data collection is very costly. Consequently, a 3D-simulation model was developed based on a cross-platform game engine. This model generates virtual wood stacks based on a data set of logs which are defined by the user. The simulation of a stack can be done in a few seconds only and each stack generated can be visualized once all iterations are done. The simulation results are the stacked cubic volume, solid wood cubic volume, and the respective conversion factors. The model, fed with both real data and user-defined data, allows for a detailed analysis of the effect of each parameter on the results, as the user can vary their values discretionary. To obtain the first results from real data, 1000 logs of Scots pine (Pinus sylvestris L.) were measured. The first simulations based on these data show reliable results and it is possible to quantify the influence of the proportion of crooked wood in a pile on the stack volume and the conversion factor. In addition, the results are highly in line with the real trials that have already been performed in parallel. A further scientific evaluation and statistical analysis will be done in a second study phase. However, the model already provides a reasonable tool that is easy to apply for the forest and wood industry in order to make the most accurate estimate possible of the solid wood content in a wood pile.

Influence of aggressive media on mechanical properties of wood-polymer composites

Mechanical properties of two samples of decking boards were measured after exposure in rain and chlorinated water, in ice, and in a mixture of gasoline and water in different concentrations from 1 to 7%. Samples consisting of 60% wood flour, 30% polyvinyl chloride and 10% additives were used for measurements. Additives are flame retardants, stabilizers, modifiers and dyes. The mineral filler CaCO3 was used as modifiers. For sample №1, the CaCO3 content was 42% and the wood content was 18%. For sample №2, the CaCO3 content was 24% and the wood content was 36%. As a result of measurements after exposure for 150 days, it was found that the specific impact strength increases by 120%, the bending strength decreases by 60%, and the Shore D hardness decreases by a maximum of 10%. Consequently, decking boards can be confidently used for a long time, since a number of properties almost do not change, but even increase, and some decrease in strength remains within acceptable values.

Plasma Treatment of Polypropylene-Based Wood–Plastic Composites (WPC): Influences of Working Gas

In this study, a polypropylene (PP)-based wood–plastic composite with maleic anhydride-grafted polypropylene (MAPP) as a coupling agent and a wood content of 60% was extruded and specimens were injection molded. The samples were plasma treated utilizing a dielectric barrier discharge (DBD) setup with three different working gases: Ar/O2 (90%/10%), Ar/N2 (90%/10%), and synthetic air. This process aims to improve the coating and gluing properties of the otherwise challenging apolar surface of PP based wood–plastic composites (WPC). Chemical analysis with X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) showed the formation of oxygen-based functional groups on the surface, independently from the working gas used for the treatment. Laser scanning microscopy (LSM) examined the surface roughness and revealed that the two argon-containing working gases roughened the surface more than synthetic air. However, the contact angle for water was reduced significantly after treatment, revealing measurement artifacts for water and diiodomethane due to the severe changes in surface morphology. The adhesion of acrylic dispersion coating was significantly increased, resulting in a pull-off strength of approximately 4 N/mm2, and cross-cut tests assigned the best adhesion class (0), on a scale from 0 to 5, after plasma treatment with any working gas.

Development and characterization of novel castor oil-based polyurethane composites containing wood sawdust and rubber tire powder

New eco-friendly composites consisting of castor oil-based polyurethane (PU) resin, wood sawdust, and rubber tire powder were produced, and the morphological, physical, and flexural properties were investigated. The composites were composed of varying the concentration of the PU matrix (30, 40, and 50 m%) and the wood-to-rubber ratio of the disperse phase (100/0, 90/10, 80/20, 70/30, 60/40, and 50/50 m%/m% wood/rubber, respectively). The morphology of the composites was studied by optical microscopy and scanning electron microscopy, and the flexural properties, water absorption (WA), and thickness swelling (TS) were also investigated. The analysis of variance was used to study the effect of each factor (PU content and wood/rubber ratio) on the characteristics of the composites. PU/wood/rubber composites were successfully molded and their characteristics are promising for commercial use. According to the results, the composites presenting higher wood content (high wood/rubber ratio) showed higher modulus of rupture and modulus of elasticity values, although the addition and the increase of rubber content decreased these properties. Moreover, increasing PU or reducing the wood/rubber ratio significantly reduced the WA and TS, improving dimensional stability.

Effect of cane wood and palm kernel fibre filler on the compressive strength and density of automobile brake pad

The study on the effect of cane wood and palm kernel as filler materials on the compressive strength and density of an automobile brake pad has been done. The Central Composite Design tool of the Design Expert 8 software was used to design percentage composition of the test samples for 20 experimental runs. To ascertain how well the factors fit in the design, the lack of fit test was performed. The analysis of variance shows that the developed models are significant and quadratic, showing that both materials affect the responses. On optimization, optimal compressive strength and density of 107.3 MPa and 1.73 g/cm3 were obtained for the composition of 30% resin content, 21.329% palm kernel fibre content and 40% cane wood content. Thus, the combination of cane wood and palm kernel fibre as filler material for brake pad production will give an automobile brake pad with good compressive strength and density.

Properties of Injection Molded Biocomposites Reinforced with Wood Particles of Short-Rotation Aspen and Willow

Injection molded biocomposite specimens were prepared by using four different weight percentages, i.e., 10%, 20%, 30%, and 40% of aspen (Populus tremula L.) and willow (Salix caprea L.) wood particles in a biopolymeric matrix. Dog-bone test specimens were used for testing the physical, mechanical, and thermal properties, and microstructure of biocomposites. The tensile and bending strength changed with the change in weight percentages of wood particles and the bending stiffness increased with the increasing weight percentage of wood. In Brinell hardness, similar changes as a function of wood particle weight percentage were shown, and a relationship between hardness and tensile strength with wood content was also investigated. The prepared biocomposites could be an alternative for plastic-based materials and encourage the use of fast growing (aspen and willow) wood from short-rotation forests in biocomposites.