# Moisture Measurement in Paper and Cardboard Packaging Waste Bales for Recycling
###### Abstract
determined the dielectric factor of cellulose to be 4.35, which can be a reference for the cardboard and paper bales studied on the current work. Some devices have an output voltage which is linearly related with the change in the capacitance, as shown in [PERSON] et al. [9]. Additionally, [PERSON] et al. [10] explored the dielectric properties of materials to determine the moisture content in dates by using parallel plates, having reached promising results by correlating the voltage measurements and moisture contents of the fruits sampled. According to [PERSON]'s definition [11], the dielectric constant of a material is associated with its capacity to store energy in its electric field, and the loss factor is associated with the ability of that material to absorb or dissipate energy, which has been converted from electrical to thermal energy. According to the same author, the electric capacitance of two conducting parallel plates separated by an empty space will be multiplied by the dielectric constant value of a material occupying that same space [11]. Therefore, the greater the dielectric constant of the material between the two parallel plates, the greater the final measured voltage. In the present work, the material in which the moisture content was measured was paper and cardboard packaging waste. It was used a commercially available equipment that combined the measurement of an electric voltage and the measured reaction to an electric field of water, of which the dielectric constant was approximately 82 [12], and other materials, including cardboard, paper and air, with dielectric constants ranging between 1.0 to 4.0. The equipment used included a 60 \(\times\) 10 cm flat plate that was inserted into each bale and through which an electric field was passed to measure the water present in the middle of the bale. This is a noninvasive method, in that the bales do not have to be undone to perform the measurements. This technology, coupled with portable equipment that is easy to use and handle, enables fast moisture measurement in paper and cardboard packaging waste bales. This can be a piece of technology that helps with the day-to-day separation and treatment of these materials, since it will save time in the acquisition of quality data on the bales produced, having a primary focus on their moisture content. In this way, cooperation between the stakeholders of the transaction chain of these recyclables is increased. This is possible if the bales are usable, allowing the introduction of material tracking methods along the entire value chain. This type of technology may have disadvantages of the effective depth of measurement, the occurrence of interference due to the presence of contaminants such as metals, fats or surface water as well as the inevitable contamination from the transport and handling of bales. In order to test and validate the reliability of the method inherent to the equipment, it is important to perform a calibration for the type of materials in a given market where the equipment is used so that the obtained moisture results are reliable and generate agreement among the stakeholders. According to [PERSON] [13], the most reliable way to calibrate a device for measuring moisture in this type of operation (i.e., one having constant material type and arrangement conditions) is the empirical calibration of the permittivity of the materials regarding a reference method, as is the case with the gravimetric method. The authors considered this to be the most reliable method, though it is one that consumes more time. Regarding the dearth of papers dedicated to the nondestructive moisture content measurement of paper and cardboard, the present study aims to produce some data to correlate the voltage measurements and the moisture content of the wastewater and cardboard bales.