Textiles are materials with many useful properties, such as pleasant touch, porosity, absorbency, flexibility, stretchability, and elasticity. By choosing the appropriate manufacturing technology and structure, i.e. with mechanical functionalization, their properties can be planned. They can be additionally functionalized by finishing processes. 3D printing is a new technology that creates functional objects with a pre-planned geometry by adding material to a selected surface. 3D printing on selected textile surfaces opens up new possibilities for the rapid production of hybrid, multi-layered structures with different properties, which, in addition to the modified structure and texture, can have additional properties. For example, they are electrically conductive, they have an imposed stretched structure due to the printed elements at certain points, they are more wear-resistant, they are more rigid on selected surfaces, they are less porous on selected surfaces, etc. Compared to woven fabrics, knitted fabrics are generally more stretchable, elastic, and porous. The research shows that they are a suitable substrate for 3D printing. The main purpose of the research was to determine how 3D printing with different polymers changes the mechanical properties, appearance, and structure of knitted fabrics. The research aimed to test the suitability of fine warp and circular weft knitted fabrics of different raw material compositions and structures for functionalization with 3D printing and to investigate the basic functional properties of knitted fabrics functionalized by 3D printing compared to unprinted knitted fabrics. TPU polymer filaments were found to be more suitable than PLA polymer filaments for printing on knitted fabrics. 3D printing reduces the air permeability and thermal conductivity of knitted fabrics because the polymer fills the pores in the knitted structure and increases its thickness. It was also found that all 3D printed knitted fabrics tested, except for the 100% cotton weft knitted fabric, had very poor abrasion resistance.
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