A Mathematical Solution for Calculating the Springback of Laminated Beech Stacks Molded within the Elastic Range

The springback effect in molded wood laminations within the elastic range has, to date, not yet been mathematically described. Once cured, residual internal stresses within the laminations cause the final form to deviate from that of the die. Test pieces of beech laminations of 1 mm, 2 mm and 4 mm thicknesses and stack sizes of between 2 and 16 laminations were used. The elasticity value of each stack was obtained using non-glued laminations in a three-point bending test within the elastic region. The laminations were glued with polyurethane resin and mounted in a radius form die. The stress induced by the die onto the stack is within the elastic region of the material without any prior chemical or physical plasticisation of the wood. After curing was complete and the laminations removed from the die, the actual radius was calculated using a circular equation within the CAD program, using three measurement points taken from the stack. The radius of the die within the limits of this study has a negligible effect when predicting the springback of the stack. The exponential correlation between springback and the number of laminations, was used to calculate the springback effect on molded laminated stacks.

Resistance of Injection Molded Wood-Polypropylene Composites against Basidiomycetes According to EN 15534-1: New Insights on the Test Procedure, Structural Alterations, and Impact of Wood Source

In this study, we investigated injection molded wood-polypropylene composites based on various wood sources and their decay resistance against white rot (Trametes versicolor) and brown rot (Coniophora puteana) in a laboratory test according to EN 15534-1:2014. The manufactured composites consisted of poplar (Populus spp.), willow (Salix spp.), European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) H. Karst.), and a commercial wood source (Arbocel® C100), respectively. All formulations were compounded on a co-rotating twin screw extruder and subsequently injection molded to wood–PP specimens with a wood content of 60% or 70% by weight. It was found that the test procedure had a significant effect on the mechanical properties. Loss in mechanical properties was primarily caused by moisture and less by fungal decay. Moisture caused a loss in the modulus of rupture and modulus of elasticity of 34 to 45% and 29 to 73%, respectively. Mean mass and wood mass losses were up to a maximum of 3.7% and 5.3%, respectively. The high resistance against fungal decay was generally attributed to the encapsulation of wood by the polymer matrix caused by sample preparation, and enhanced by reduced moisture uptake during the preconditioning procedure. Notable differences with respect to the wood particle source and decay fungi were also observed. Structural characterization confirmed the decay pattern of the fungi such as void cavities close the surface and the deposition of calcium oxalates.

Improvement of Mechanical Properties of Injection Molded Wood/Polypropylene Composites Parts with Ultrasonic Oscillation Assistant

Due to the water absorption of wood fillers and poor adhesion between wood fillers and polymer matrix, the loosen material structure always appears in wood/polymer composites after injection molding process, which results in reduced composites mechanical properties. In this study, two kinds of wood particles with different sizes and properties were compounded with Polypropylene (PP) in highly filled level (by 50% and 60% weight concentration). The experimental tensile test samples were prepared by one double-gate injection mould integrated an ultrasonic generator unit. The experiments were carried out for studying how the ultrasonic output power and the oscillation inducing time affect the injection molded wood/PP composites mechanical properties. 3 output power levels (400W, 600W and 800W) and 2 inducing mode were set (Mode1. the oscillation is induced from injecting moment to ejection moment; Mode2. the oscillation is induced from injecting moment to packing procedure finishing). The results show that the E module, tensile strength and density of the test parts are obviously changed with various ultrasonic output power and inducing time. Comparing the mechanical properties of parts with and without ultrasonic assistant indicates that the ultrasonic oscillation is a practical method to improve mechanical properties of injection molded wood/PP composites parts.