ABSTRACT:The main benefits of incorporating wood fibers (WF) in plastics are the increased stiffness and lowered cost of the resulting composites. However, these improvements are usually accompanied by a reduction in the ductility and impact resistance. These shortcomings can be removed by effectively foaming and incorporating a finecelled structure in these composites. The volatiles released from WF during processing are known to deteriorate the cell structure. The maximum processing temperature, which affects the amount of volatiles released by the WF during extrusion of fine-celled plastic/WF composite, affects the cell morphology. This study was undertaken to identify the critical temperature above which the cellular structure of WF composite foams is significantly deteriorated. To clearly identify the effects of the volatiles generated from WF on the cellular morphology, neither a chemical blowing agent nor a physical blowing agent was used in the foam processing. The experimental results show that regardless of the drying method, the highest processing temperature of plastic/WF composites should be minimized, preferably below 170°C, to avoid the adverse effects of the volatiles generated from the WF during processing. A method of estimating the emissions from WF during extrusion processing by using the TGA data is also proposed.

The large quantity of moisture in wood‐flour may lead to the deterioration of the cell structure of foamed plastic wood‐flour composites in terms of cell size, non‐uniformity, and poor surface quality. Since these anomalies can cause poor mechanical properties of the foamed composites, the removal of the moisture from wood‐flour becomes a critical issue with respect to the improvement of these properties. The wood‐flour in this experimental study was first oven‐dried at different temperatures and then subjected to acetone extraction and thermogravimetric analysis (TGA). The oven‐dried wood‐flour was blended with plastic and then subjected to extrusion foaming. The results obtained from the TGA studies indicate that most volatiles were released from the extractives. Conversely, a comparative experimental study of the foaming behavior of these plastic/wood‐flour composites versus that of undried wood‐flour composites confirms that removal of the adsorbed moisture from wood‐flour results in a better cell morphology. However, it seems that some gaseous emissions released from wood‐flour are soluble in plastic and thereby favorably contribute to the development of the cell morphology. This paper describes the expansion mechanisms of wood‐flour composite foams resulting from the adsorbed moisture and dissolved gaseous emissions as well as resulting from the finely dispersed undissolved gas bubbles released from a chemical blowing agent.

The dolomite dust-emulsified asphalt composite with excellent mechanical properties was successfully prepared using alkali activation. The effects of different alkali concentrations and emulsified asphalt contents on the mechanical properties of the materials were studied. The mechanical properties and microstructure of the composites were analyzed using compressive strength tests, bending strength tests, and SEM characterization. The experimental results show that the specimens have excellent mechanical properties: the 7-day compressive strength can reach 76.67 MPa, and the bending strength is about twice that of silicate-based geopolymer-emulsified asphalt composite. With an increase in emulsified asphalt content, the compressive strength of the samples decreases, while the bending strength increases first and then decreases. When the emulsified asphalt content is 1%, the bending strength of the sample is up to 28.81 MPa, which is 25% higher than that of the sample without emulsified asphalt. This indicates that an appropriate emulsified asphalt content can play a toughening role in the system, providing a new idea for designing high-toughness alkali-activated materials.

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