*2.2.1. Aspect ratio of fillers*

A digital microscope (Keyence VHX-100, Japan) and the corresponding imaging system were used for the aspect ratio determination. About 500-mg fillers of each filler type, classified by the sieve opening, were placed on a glass dish under the microscope. The optical light was adjusted to achieve the best focusing alignment and image resolution. The filler images taken with a digital camera were used to measure the length and diameter of individual filler particles. A minimum of 100 filler particles were measured for each sample. The aspect ratio was described as the ratio of length and width of the fibrous wood and as length and width of the rice husk platelets. Note the latter were not characterized by the length-to-plate-thickness ratio.
