## 1 Introduction
The achievement of equilibrium is primarily influenced by sorption, which is directly related to the contact or wetting of water on the surface of the material. However, complete wetting of the thermoplastic with water does not occur because the surface tension of the water (72.5 dynes/cm) is too high. For wetting to occur, the surface energy of the polymer must exceed 72.5 dynes/cm, which can only be achieved by physical surface treatment or chemical modification [9]. The swelling of polymers is a phenomenon in which polymer molecules absorb external factors, such as moisture, increasing the material's volume. It is an important phenomenon in various fields, such as chemistry, pharmacy, and materials engineering. The swelling of polymers is closely related to their structure and chemical properties. The main factors influencing swelling include interactions between polymer molecules, van der Waals forces, electrostatic interactions, and the polymer's ability to absorb substances. The swelling of polymers can have both beneficial and detrimental effects. It can be used to create absorbing materials, such as hydrogels, which find applications in the medical industry. However, in some cases, swelling can lead to dimensional changes and decreased strength and durability of polymer materials [10; 11]. Plastics produced through condensation polymerization, where water is liberated as a byproduct, have the potential to undergo degradation when subjected to elevated temperatures in the presence of water. Polyesters like polyethylene terephthalate (PET) or polylactide (PLA) are susceptible to a degradation mechanism known as hydrolysis, wherein the polymer chains are cleaved when exposed to acidic, alkaline, or certain neutral environments. Figure 1 shows the mechanism of the alcoholysis reaction of lactic acid polymer under the influence of alcohol [12; 13]. All of the abovementioned properties of polymers can have significant importance and impact on the properties of objects printed using the L-FDM technique (Figure 2). The method was first described in the publication titled \"Liquid for Fused Deposition Modeling Technique (L-FDM)--a revolution in application chemicals to 3D printing technology. Colour and elements\". Previously published by the authors of this publication, it involves passing a filament (thermoplastic polymer in the form of a 1.75 mm diameter filament) through a liquid modifier or a modifier solution in an organic solvent. In this study, which is the second publication on the innovative L-FDM printing technique, the authors will focus on the new properties of L-FDM printed parts, in the example of commonly used PLA and PET-G filaments. Alcohol solutions of organosilicon compounds were used, which are commercially available. The influence of organic solvents on the properties of L-FDM pr  
Figure 1: Mechanism of the alcoholysis reaction of lactic acid polymer under the influence of alcohol. Alcohols used in the experimental part by the researchers are presented as examples of substrates that may take part in the alcoholysis reaction. Figure 2: A short concept of a new printing technique—Liquid to Fused Deposition Modeling (L-FDM)—(**a**) polymer material spool, (**b**) a filament, (**c**) modifying substance solution or liquid modifying substance, (**d**) drying of the modified filament, (**g**) traditional FDM printing (**e**) extruder, (**f**) heating block with nozzle, (**h**) 3D printed part.