INTRODUCTIONThe concept of organic agriculture, which firstappeared in European countries, has gained itspopularity in Russia in the last few years. Accordingto the concept, agricultural industry should ensure theenvironmental and biological safety of technologies, rawmaterials, and products [1–3]. In Russia, a new federallaw on organic products comes into force in 2020 thatregulates the activity of agricultural enterprises. Itprohibits the use of packaging and transport packagewhich damages to the environment and encouragesthe application of methods and technologies aimedat ensuring a favorable state of the environment,strengthening human health, as well as at maintainingsoil fertility.Besides, one of the problems is the utilization ofagricultural wastes, which are currently mainly storedor disposed. Only a small part of them is used toproduce coarse low-value feed and bedding for animals,fertilizers, or fuel [4]. These include straw, flax shive,coffee grounds, nutshells, plant waste from cereals andflour manufacture, as well as from fruit and berriesprocessing. In Russia, efficient agricultural enterprisesgenerate several million tons of such waste annually.In the Altai Territory, for example, the amount of grainhusks obtained at elevators is on average 2–3 milliontons per year [5].One of the alternatives of plant waste recyclingis the production of bioplastics and paper [6–9]. Inthe world practice, plant fillers from cereal husks150Glukhikh V.V. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 149–154and agricultural plant fibers are widely used in theproduction of biocomposites and reinforced bioplastics.They can be produced both from plant materialsonly and with the addition of classical petrochemicalproducts [10–12]. The improved technologies andperformance characteristics of bioplastics as well asproduction cost reduction make it possible to fill newniches in the market [13]. Bioplastics without adhesivesubstances based on plant materials are environmentallyfriendly. Plant materials can be wood powder, sawdust,cereal husk, as well as flax and hemp fibers [6, 13].Such plastics are biodegradable materials, and theirdegradation is due to microbial enzymes [14–16].The use of plant biodegradable plastics, includingplastics without adhesives, to produce containers with ashort life cycle, building and packaging materials can bea promising way for agricultural waste recycling, whichcorresponds to the concept of organic agriculture [7,17, 18].Taking into consideration the obvious advantages ofbiodegradable plastics, the study of the main physicaland-mechanical properties of plant plastics withoutadhesives obtained from millet husk and wheat husk andanalysis of their biodegradation potential are relevant.STUDY OBJECTS AND METHODSThe objects of the study were plastic sampleswithout an adhesive substance based on wood and plantmaterials. The samples were made at the Ural StateForestry University. Wood-based plastics made fromindustrial sawdust (State Standard 18320-78I) were usedas control samples. Experimental samples were plantplastics obtained from millet husk and wheat husk,cereal production wastes.The plant fillers of 18.0 and 30.0 g in mass weresubjected to pressing to obtain disks of 2.0 and 4.0 mmin thickness and 90 mm in diameter (moisture contentof the molding material was 12%). The conditionsof pressing were as follows: molding material mass,10.0 g; pressing pressure, 124.0 MPa; pressing time,10 min; and cooling time under pressure, 10 min. Thephysical-and-mechanical characteristics of the sampleswere analyzed both before and after biostability andbiodegradation tests. We determined water absorption(State Standard 4650-80II) and strength parameters suchas density, flexural strength, hardness, elasticity number,compression elasticity modulus, elastic modulus inflexure, breaking stress, yield strength (State Standard4648-71III, State Standard 4670-77IV, State StandardI State Standard 18320-78. Technological wooden sawdust forhydrolysis. Specifications. Moscow: Izdatelʹstvo standartov; 1986. 7 p.II State Standard 4650-80. Plastics. Methods for the determination ofwater absorption. Moscow: Izdatelʹstvo standartov; 2008. 7 p.III State Standard 4648-71. Plastics. Method of static bending test.Moscow: Izdatelʹstvo standartov; 1992. 11 p.IV State Standard 4670-77. Plastics and ebonites. Method fordetermination of hardness by ball indentation under a given load.Moscow: Izdatelʹstvo standartov; 1992. 6 p.10634-88V).To study biodegradation potential, the test sampleswere kept in soil for 21 days, then the main visualmorphological characteristics of their biodegradationwere evaluated. Soil was prepared in accordance withState Standard 9.060-75VI. At the beginning of the test,pH of the soil extract was 7.0 and biological activitycoefficient was 0.8. The soil microbiocenosis wasformed by native field strains of microorganisms of theinitial components of the soil.We observed such biodegradation signs as splitting,swelling, loosening, macro- and microcavitiesformation, changes in the shape and size of the mainplant component particles, fibrillation and fragmentationof particles, the local discoloration of the sample,the presence of colonies of microorganisms, hyphae,fungal fruit inside or on the sample surface, as well asits mucilagination. The samples that did not displaybiodegradation signs were tested for strength and waterabsorption.In addition, the test with the germination of oatand clover seeds on a substrate containing the samplesunder study was carried out. For this, the substrate wasprepared that included two layers of multi-purpose soil(60%) alternating with two layers of the samples (40%).Multi-purpose soil was used as control sample. Oat andclover seeds were sown in the substrate, germinatedfor 21 days, after that growth rate, as well as stem andleaves formation were evaluated in the experimentaland control samples. The root system of the plants wasdetermined in visible light and in ultraviolet light.RESULTS AND DISCUSSIONWe analyzed the physical-and-mechanical parametersof plant plastics based on husks of millet andwheat and wood plastic based on sawdust. The samplesdid not include adhesives. The analysis showed that thestrength characteristics of the wood-based samples werehigher than those of the plastics based on millet husk,especially flexural strength. Thus, the average density ofwood plastics exceeded that of plant plastics from millethusk by 10%, hardness by 40%, compression elasticitymodulus by 50%, and flexural modulus by 3.9 times(Figs. 1 and 2).A comparative analysis of the physical-andmechanicalproperties of the wood plastic samples withthe samples of plant plastics from wheat husk showedsimilar results. Thus, the average value of the densityof the wood-based plastics exceeded that of the plantsamples from wheat husk by 15%, hardness by 10%,compression elasticity modulus by 10%, and flexuralmodulus by 2.6 times.V State Standard 10634-88. Wood particle boards. Methodsfor determination of physical properties. Moscow: Izdatelʹstvostandartov; 1991. 10 p.VI State Standard 9.060-75. Unified sуstem of corrosion and ageingprotection. Fabrics. Method of laboratory tests for microbiologicaldestruction stability. Moscow: Izdatelʹstvo standartov; 1994. 9 p.151Glukhikh V.V. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 149–154According to the results of the comparative analysisof the physical-and-mechanical properties of the twoplant plastic samples, the average values of hardness,compression elasticity modulus, and elastic modulus inflexure of the plastic from millet husk were higher thanthose of the samples based on wheat husk by 1.3, 1.3, and1.5 times, respectively.An increased pressing temperature (from 180 to170°C) led to an improvement in the physical-andmechanicalproperties of the plant plastics compared tothe wood-based samples. Thus, the values of elasticitynumber, the elasticity moduli, breaking stress, andyield strength increased. Presumably, this is due to thedifference in the dynamics of lignin polymerizationreactions in wood and plant plastics. This factor shouldbe taken into consideration when selecting pressingconditions.The study of the biodegradation potential of plasticswithout an adhesive component based on wood sawdust,millet husk, and wheat husk showed that all the samplesstudied had a relatively equal high biodegradationpotential.We analyzed the morphological signs ofbiodegradation of the materials kept in active soilfor 21 days. The analysis showed that all the sampleshad surface mucilagination, edge swelling, and localdiscoloration of the surface (Fig. 3).60% of the samples based on millet husk, 58% of thesamples from wheat husk, and 47% of the wood plasticsbased on sawdust displayed longitudinal and transversesplitting, loosening, and macrocavities formation(Fig. 4). The splitting and loosening sites ranged from1.5 to 5.5 mm in size.Microscopy was used to assess signs of thesample destruction. The analysis revealed marginalfibrous structure; the fragmentation and destructionof individual particles of the plant component; focaldarkening of particles; and microcavities formationbetween the particles of plant material. Moreover, all thesamples under study showed bacterial contamination.74% of the samples with millet husk, 85% of the samplesfrom wheat husk, and 62% of the wood samples hadFigure 2 Average values of compression elasticity modulus,breaking stress, yield strength, and elastic modulus in flexureof plastics without adhesiveselasticmodulusin flexure,MPa 10–3compressionelasticity modulusMPa 10–1breaking stress,MPayield strength,MPa(1) wood plastic (2) plant plastics from millet husk(3) plant plastics without from wheat husk1 32Figure 3 Plant plastic from millet husk, plant plastic fromwheat husk, and wood plastic kept in active soil for 21 days(all plastics are made without adhesives)Figure 4 Wood plastic fragment with signs of splitting,swelling, marginal and longitudinal fragmentationFigure 1 Average values of density, hardness,and elasticity number of plastics without adhesives(1) wood plastic (2) plant plastics from millet husk(3) plant plastics without from wheat huskdensity, kg/m3 10–2 hardness, MPa elasticitynumber, %1 2 38060402006040200152Glukhikh V.V. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 149–154multiple large colonies of mold fungi of different growthphases (Fig. 5).The plant plastics demonstrated a more pronouncedbiological destruction compared to the wood samples.Thus, they had changes throughout the sample, while thewood plastics were characterized by edge and surfacechanges.Further, we evaluated the growth rate and organsformation of oat and clover grown on control andexperimental substrates. Multi-purpose soil was used asthe control substrate, while the experimental substratecontained multi-purpose soil and the samples understudy. According to the results of the experiment,morphological signs of retardation and deviation inthe oat and clover development were not detected. Theroot system of the plants did not also have significantdifferences. The roots penetrated into the plant andwood samples, fragmenting them. The soil – rootconglomerate was analyzed in ultraviolet light. Theresult was typical of these plant species; no dependenceson the presence of the samples under study in thesubstrate were found (Fig. 6).Based on the sings found, the plastics with wheathusk had the highest degree of biodegradation among allthe samples under study.The keeping of the plant and wood samples inactive soil for three weeks led to thier physical-andmechanicalproperties deterioration. Then, hardnessdecreased by 66, 70, and 62%, elasticity number by43, 47 and 46%, and compression elasticity modulusby 76, 80, and 73% for the wood plastics, plant plasticsfrom millet husk, and plant plastics from wheat husk,respectively. Breaking stress and yield strength valuesdecreased by 64% and 63% for the wood-based plasticsand by 60% and 68% for the plant-based samples,respectively.A comparative analysis of flexural strength valuesof the plastics under study without adhesives showedthat the highest average value of this indicator was forthe wood plastic samples (4 MPa), and the lowest forthe plant plastic based on wheat husk (1 MPa). Waterabsorbingcapacity was 96, 85, and 94% for the sampleswith wheat husk, with wheat husk, and with sawdust,respectively.CONCLUSIONAccording to the results of the study, plant plasticobtained under the same pressing conditions which areused for wood plastic production had lower strengthcharacteristics. A decrease in the pressing temperatureby 10°C improved such strength characteristics of thehusk-based samples as elasticity number, moduli ofelasticity in compression and flexure, as well as breakingstress. Also, the wood and plant plastics withoutadhesives based on sawdust, millet husk, and wheathusk were found to have a high biodegradation potential.Therefore, it makes it possible to utilize such materialsnaturally, i.e. without composting, in contrast withbiodegradable wood-polymer composites.On the other hand, a high biodegradation potentialalso indicates a low biostability of materials. Specialconditions should be applied to use of products fromplant plastics based on husk of millet and wheat, aswell as from wood with sawdust. The conditionsinclude a low humidity, no contact with water and soil,or with using antiseptics and waterproofing agents.The advantages of plant plastics without adhesivesbased on agricultural waste ‒ millet husk and wheathusk ‒ include their ecological safety, relative easeof production, low cost, raw materials availability, ahigh biodegradation potential, as well as performancecharacteristics comparable to those of wood plastics.Plant plastics without adhesives obtained fromagricultural waste can be relevant in steppe regions as aninsulating, building, and decorative material.CONTRIBUTIONThe authors were equally involved in developing theFigure 5 Fragment of plant plastics from wheat husk (withoutadhesives) with signs of mold growthFigure 6 Root system of oat on a substrate with plant plasticfrom wheat husk without adhesives in ultraviolet light withluminescence foci153Glukhikh V.V. et al. Foods and Raw Materials, 2020, vol. 8, no. 1, pp. 149–154research concept, obtaining and analyzing data, as wellas in writing the manuscript.CONFLICT OF INTERESTThe authors state that there is no conflict of interest.