The paper sheets were produced using a laboratory sheet former from secondary fibers extracted from the unprinted parts of cigarette packages. Additives synthesized from the natural resins shellac and rosin, were chemically modified with glycerin and propylene glycol to be used as structure modifiers in order to improve hydrophobicity and mechanical properties of produced paper sheets. The additives were thoroughly characterized using Fourier-transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), and Matrix-Assisted Laser Desorption/Ionization (MALDI) techniques. The acid, hydroxy, saponification, and ester values were also determined. It was shown that the additives synthesized in this work reduce capillary water absorption according to the Klemm test, increase the contact angle between water and the paper surface from 86° to more than 122°, and extend the time required for a water droplet to be absorbed. The addition of synthesized additives increased the tensile strength (breaking length) up to 31% and improved the Dynamic Mechanical properties (DMA) of the paper sheets. Moreover, the biodegradability and recyclability of the paper were also evaluated, demonstrating that the presence of additives does not adversely affect these properties compared to the reference paper without additives. The overall concept of the developed technology is fundamentally based on the principles of green chemistry and circular economy. The integration of such additives also aligns with Agenda 2030 and United Nations Sustainable Development Goal 9, promoting industry, innovation, and infrastructure.
Milošević et al. (Sun,) studied this question.