# In Situ and Partial In Situ Synthesis of Cellulose Magnetic/Maghemite Composites
## 1 Introduction
In their study, the cellulose was dissolved directly into sodium hydroxide/urea aqueous solution pre-cooled to \(-\)12 \({}^{\circ}\)C, and the resulting solution was centrifuged at 8000 rpm for 20 min at 15 \({}^{\circ}\)C for degasification and then cast on a glass plate and immersed into 5 wt% H\({}_{2}\)SO\({}_{4}\) solutions for 5 min to coagulate and regenerate. Then, the obtained wet films were immersed in an aqueous ferric chloride (FeCl\({}_{2}\) or FeCl\({}_{3}\)) solution with different concentrations for 1 day and then treated with an aqueous sodium hydroxide solution (4 M) for 20 min, followed by rinsing with deionized water several times. The composite films were fixed on a poly(methyl methacrylate) plate and dried at ambient temperature. The saturation magnetization obtained has values between 0.5 and 2.5 emu/g. In other work, [PERSON] et al. presented a rapid sonochemical in situ co-precipitation approach in order to prepare magnetite/cellulose nanocomposites [13]. Differing from the conventional method, this proposed in situ co-precipitation reaction was performed under atmospheric conditions without azote purging to yield the nanocomposite. The obtained magnetic composites show a high saturation magnetization, between 20 and 35 emu/g. In another study, [PERSON] and collaborators [14] obtained cellulose microspheres by using the sol/gel transition method from cellulose drops in a sodium hydroxide (7 wt%)/urea (12 wt%) aqueous solution precooled to \(-\)12 \({}^{\circ}\)C. Magnetic magnetite/cellulose microspheres were produced by in situ synthesis of Fe\({}_{3}\)O\({}_{4}\) nanoparticles into the cellulose pores, which were used as the solid template microreactor. The saturation magnetization presents values between 4 and 8 emu/g. In another original study, [PERSON] et al. describe a new synthesis method for producing cellulose-ferrite micro- and nano-composites using a mixture of Fe\({}^{*2}\)/Fe\({}^{*3}\)[15]. Another issue of interest is the superparamagnetic phenomenon (SP), which represents the state of a single magnetic domain-sized grain when the thermal energy is enough to overcome barriers to a reversal of magnetization. These barriers are proportional to grain volume and can arise from shape anisotropy, magnetoelastic anisotropy, or magnetocrystalline anisotropy. When the energy barriers are large with respect to thermal energy, the magnetization process is stopped with the consequence that the probability of spontaneous reversal magnetization decreases drastically. If the barriers are low, thermal excitations can result in the reversal of the magnetization in a very short time, and the grain is in a SP state. For a specific temperature, the volume at which a particle goes from being in an unblocked state to a blocked state is known as the blocking volume. For this specific volume, we can block the grain by lowering the temperature below the blocking temperature (the temperature at which the reversal magnetization begins) [7; 16]. Depending on the material, this type of magnetism occurs in small ferrimagnetic or ferromagnetic particles and implies sizes from a few nanometers to a couple of tenths of nanometers [17; 18]. These nanoparticles are single-domain particles, so the total magnetic moment can be regarded as one giant magnetic moment, composed of all the individual magnetic moments of the atoms that form the nanoparticle [19]. The size factor is not the only element that can provide a state of SP. The surface effects [20; 21] and the crystallinity affect the magnetic properties and the SP phenomena [22; 23]. The main interest of the study of these materials is represented by biomedical applications [24]. This work presents a classic co-precipitation method modified by using ultrasound to obtain a ferromagnetic cellulosic composite in situ and partially in situ. Thus, cellulose/magnetic/maghemite composites with varying proportions (73.4/8.1/18.5% for total in situ and 74.6/12.5/12.9% for partial in situ) and different magnetizations were obtained.