Study on Physicochemical Properties of Biocomposite Films with Spent Coffee Grounds as a Filler and Their Influence on Physiological State of Growing Plants

Abstract

The aim of the study was to plasticize corn starch with two selected urea (U)-rich plasticizers: choline chloride (CC):U or betaine (B):U eutectic mixtures at a molar ratio of 1:5 with a presence of spent coffee grounds as a filler. The biomaterials were prepared via a solventless one-step extrusion method and then extrudates were thermoformed using compression molding into sheets. The materials were characterized using mechanical and sorption tests, TGA, DMTA and FTIR. Additionally, a study on the biodegradation and remaining nitrogen content in soil was conducted. For the first time, an influence on physiological state of growing plants of the materials presence in soil was investigated. The addition of the coffee filler slightly increased the mechanical properties and decreased the swelling degree of the materials. The DMTA results indicated that biocomposites were easily thermoformable and the high filler addition (20 pph per polymer matrix) did not affect the processability. According to the biodegradation test results, the materials disappeared in soil within ca. 70 days. The results from this study on the physiological state of growing plants revealed that the materials, especially plasticized with CCU, did not exhibit any toxic effect on the yellow dwarf bean. The percentage of total nitrogen in the soil substrate in comparison with the control increased indicating an effective release of nitrogen from the TPS materials into the substrate.

Biocomposites Based on Wheat Flour with Urea-Based Eutectic Plasticizer and Spent Coffee Grounds: Preparation, Physicochemical Characterization, and Study of Their Influence on Plant Growth

“…This study, for the first time, shows the application of DES for effective thermoplasticization of WF. In the literature so far, mostly thermoplastic starch, e.g., in works [ 17 , 18 , 20 , 23 , 24 , 49 ] or wheat gluten processed with DES presence [ 55 , 56 , 57 ] have been described. One exception could be Ma and coworkers’ study [ 15 ], where a mixture of urea and formamide was used to plasticize WF into materials with high EB, but the DES formation between co-plasticizers was not mentioned.…”

“…Before further tests, the films were stored in a climate room at 23 °C, 50% RH, for several days. A scheme of the biocomposite preparation is shown in the previous work [ 49 ].…”

“…The dried samples were then weighed and placed in a climate chamber (BINDER KBF 115, Tuttlingen, Germany) at relative humidity—RH 50 ± 2%, temperature 25 ± 2 °C for moisture degree determination or immersed in distilled water for 24 h for the determination of swelling and solubility degrees. Then, the samples were weighed, and the parameters were calculated as in our previous work [ 49 ].…”

“…The studied variants (control and with the biocomposite) were irrigated using a drip line. Gas exchange parameters, chlorophyll “a” fluorescence parameters, and the determination of photosynthetic pigments and proline content were measured according to the methodology described in our previous work [ 49 ].…”

“…Coffee as a food byproduct can be applied for biomass gasification, biodiesel production, and sorbent-removing metal ions [ 41 , 44 ] as a filler for bioplastics [ 34 , 37 , 38 , 45 ]. However, there are only a few works related to thermoplastic starch (TPS) with cf or other coffee byproducts [ 46 , 47 , 48 , 49 ]. Additionally, few works described TPWF composites, i.e., with flax [ 50 ], sisal [ 12 ] cotton [ 10 ], or bran fibers [ 51 ], but there are no studies with thermoplastic wheat flour with cf.…”