5.3.10 Gel PointThe lowest solid content at which a fiber suspension forms an interconnected network is called the gel point, and it is related to the fiber aspect ratio. This technique has proved to be an excellent and simple tool to evaluate the CNF quality through the comparison of the relativeshortening of fibers with diameter reduction [349].Raj and Mayahi [350] first studied the required conditions to measure the gel point through sedimentation.High yield CNF were found to produce anomalous sedimentation data because of the electrostatic repulsion from surface charges. However, with the addition of high levels of Na1 or Ca21 ions, the electrostatic interactions between fibers were reduced, thus settling normally. The aspect ratio of three different feedstocks used increased with increasing homogenization, proving that the fiber delamination dominated over fiber shortening. Then, the slope of the aspect ratio versus energy consumption showed the ease of processing of each feedstock.This technique has been used to quantify flocculation mechanisms, among others such as floc size, strength, and reflocculation ability of MFC through Focused Beam Reflectance Measurements [351]. Polyelectrolyte morphology, charge density, molecular weight, and CMF concentrationwere studied in the adsorption and flocculation of MFC. Linear Cationic Polyacrylamide and Branched Polyethyleneimine (PEI) were used as polyelectrolytes. The gel point technique allowed the authors of this study to realize that the flocculation mechanism was not purely charge neutralization. The reason was that the minimum gel point was not the point of zero charge. This was attributed to the high polydispersity of the commercial polyelectrolyte PEI used, that formed some bridges through the largest molecules thus changing the minimum gel point.