INTRODUCTIONIn the spotlight of current research and developmentare new formulations and technologies for producingplastics based on plant fibers and fillers, polymercomposites combining products of traditional petrochemistryand biotechnology, biodegradable plastics,and biopolymers [1]. We can see new trends in thedevelopment of these technologies. Many of thembecome commercialized and acquire a wide appliedsignificance in addition to their scientific value [2].Recent years have witnessed a growing interest inbiocomposites and bioplastics filled and reinforced withnatural fibers and plant components, as well as in plantbioplastics that do not contain any products of largescalepetrochemistry [3–5]. Over the last few years, theglobal market of biodiversity-based plastics has had anaverage annual growth of 40% [3]. Largely stimulatedby consumer demand, the development of bioplasticsaims to improve the performance, availability, andenvironmental sustainability of materials and products[6]. The problem of microplastic pollution has alsoattracted a lot of attention recently.The requirements for biodegradable polymers arechanging: the decomposition of a polymer matrixCopyright © 2022, Buryndin et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 InternationalLicense (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix,transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.Foods and Raw Materials, 2022, vol. 10, no. 1E-ISSN 2310-9599ISSN 2308-4057149Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154into macro- and microscopic particles is no longeran indicator of satisfactory destruction [7]. Althoughactively developing abroad for several decades,bioplastic technologies are a relatively new field ofresearch in Russia. Its President, Vladimir Putin,declared 2017 the year of ecology, which stimulateda search for low-waste and less resource-intensiveproduction methods, as well as for recycling and wastedisposal technologies to make industrial enterprisesmore environmentally friendly [8]. In line with thisconcept is the processing of wood and plant waste suchas sawdust and husks of wheat, oats, buckwheat, andother crops into environmentally friendly and practicalmaterials. Quite promising is the production of woodand plant plastics without binders [9].Russia yearly produces significant amounts of wastesuitable for recycling and processing, such as husks,oilcakes, fibers, etc. However, this waste is not widelyused to produce new materials. The reasons are a lackof effective processing technologies and equipment,financial and economic aspects, and a low marketinterest [10].To produce binder-free composite bioplastics basedon polymers and plant fillers, wood and plant bioplastics,we need to prove their high performance properties. Forexample, materials with a high rate of biodegradationcan be used for mulching or to make agrotechnicalfilms, as well as disposable containers for seedlings andsoil [11]. However, structural and finishing products,or reusable packaging, need to be highly resistant tovarious environmental factors.For this, composites are often used whose matrixcontains recycled polyethylene or polypropylene with theaddition of plant components (fibers, husks, and flour).The properties of such composites are well studied [12].For example, the resistance of wood and plant plasticsis known to be determined by the biostability of thepress material (its main components) and the absenceof molecules that are a substrate or nutrient for soil,saprophytic micro- and macroorganisms [13, 14].Polymer molecules can be destroyed physicochemically,through hydrolysis, under the action of acidicor alkaline media, or under the action of enzymesfrom fungal and bacterial cultures. Both ways ofbiodegradation are possible with binder-free plant andwood plastics [10]. They are mainly damaged by fungiand, to a lesser extent, by bacteria that cause rot anddestroy lignin [13].The shelf-life of household products made of binderfreewood bioplastics is estimated at 7.5 years if usedat room temperature and moderate humidity [15].Antiseptic protection is needed to maintain and improvetheir performance characteristics. However, materialstreated with antiseptic agents change their physical,mechanical, and operational properties [16, 17]. Thus,to fully use agricultural plant waste in recycling andproduction of new materials, we need to find themost effective methods to increase their resistance tobiodegradation.In this regard, it seems relevant to study thebiostability of binder-free wood and plant plastics basedon sawdust, wheat and millet husks, as well as to find anoptimal way of their antiseptic protection. Our aim wasto study the biodegradation of wood (based on sawdust)and plant (based on millet or wheat husks) plasticsproduced without binders and treated with antiseptics.For this, we analyzed the biostability of the samplesof binder-free wood plastics (BF-WP) and binder-freeplant plastics (BF-PP), assessed the effect of antisepticson their physical and mechanical characteristics, andanalyzed the biostability of the samples antisepticallyprotected by different methods.STUDY OBJECTS AND METHODSOur study objects were the antiseptically treatedsamples of binder-free wood plastic (BF-WP) based onsawdust and binder-free plant plastic (BF-PP) based onwheat and millet husks. The samples were 2–4-mmthickdiscs, 90 mm in diameter, made by pressing fromraw materials containing the plant component (sawdust,wheat or millet husks). The weight of the press materialwas 10 g per disk. The pressing time was 10 min,pressure 124 MPa, cooling time under pressure 10 min.Some of the samples were treated with antisepticcompounds by adding them to the press material or byapplying them to the finished sample after conditioning.We used a water repellent (1 g/disc), 12% CuSO4(0.6 kg/100 m2), and a Forwood antiseptic (RadugaCoating Works, Novosibirsk) (2 g/disc). The amounts ofantiseptics were based on the previous studies.Before assessing biostability, we analyzed thephysical and mechanical properties of the samples. Inparticular, we determined the density, flexural strength,hardness, elasticity number, compression modulus,flexural modulus, breaking stress, yield stress, waterabsorption, and swelling in thickness after 24 h. Then,the samples were kept in active soil for 21 days to studybiostability.The soil was prepared in accordance with StateStandard 9.060-75. At the beginning of the tests, thesoil extract had a pH of 7.0 and a biological activitycoefficient of 0.8. The soil’s microbiocenosis containednative field strains of microorganisms. After the soilexposure, the samples were analyzed for macro- andmicrovisual signs of biodegradation (splitting, swelling,loosening, cavities, morphological changes in the plantparticles, changes in color, colonies of microorganisms,hyphae, fungal fruit bodies inside or on the surface ofthe sample, sliming of the surface). Then, we examinedthe physicomechanical parameters of those sampleswhich were not damaged by the exposure in active soil.RESULTS AND DISCUSSIONFirst, we analyzed the key physical and mechanicalproperties of the control samples, namely binder-freewood plastic based on sawdust (BF-WP) and binderfreeplant plastics based on wheat husks (BF-PP-wheat)and millet husks (BF-PP-millet). We found that the150Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154exposure in active soil caused significant visual changesin both wood and plant samples. On average, 60% ofBF-PP-millet, 58% of BF-PP-wheat, and 47% of BF-WPsamples showed pronounced longitudinal and transversesplitting, edge swelling, and loosening in thickness.They also had micro- and macrocavities, especiallyalong the edges and in the splitting areas. The defectsvaried from 1.5 to 5.5 mm.All the samples featured microscopic signs ofmorphological changes in the plant particles: edgefibrillation, fragmentation and destruction of individualhusk and sawdust particles, focal darkening, andmicrocavities of different size between the particles.Surface sliming and signs of mold growth were alsofound in all of the samples. In particular, multiplelarge colonies of mold fungi in different stages ofmaturity were present in 74% of BF-PP-millet, 85%of BF-PP-wheat, and 62% of BF-WP samples (Fig. 1).On the whole, the visual signs of biologicaldegradation were more pronounced in the plant-basedsamples. The sawdust-based samples had mainly edgeand surface changes that hardly affected the middle.The exposure in active soil had a negative effecton the physical and mechanical properties of thecontrol samples, which were not treated with antisepticcompounds. The sawdust-based samples showed adecrease in hardness by 66%, elasticity number by 43%,compression elasticity modulus by 76%, breaking stressby 64%, and yield stress by 64% (Fig. 2).The plant plastics based on wheat and millet huskshad similar changes, namely a decrease in hardnessby 62 and 70%, elasticity number by 46 and 47%,compression elasticity modulus by 73 and 80%, breakingstress by 60 and 68%, and yield stress by 60 and 68%,respectively.The highest average of flexural strength was in thesawdust BF-WP samples (4 MPa) and the lowest wasin the wheat BF-PP samples (1 MPa). Water absorptionand swelling had the lowest values in the millet BF-PPsamples (85%) and the highest values in the BF-WP andwheat BF-PP samples (94 and 96%, respectively).Biostability tests showed a high biodegradabilitypotential of all the samples. Biostability can beincreased by changing the process parameters (pressingtemperature, pressure, and time) [18]. However,antiseptic treatment is the main way to reducebiodegradation. An antiseptic component can be eitheradded to the raw mixture or applied to the finishedproduct. Thus, antiseptic treatment is a prerequisitefor using binder-free wood and plant plastics in highlybioactive conditions, i.e., in an aggressive microbialdestructive environment.At the next stage, we treated the experimentalplastics with antiseptics by adding them to the pressmaterial or applying to the surface to protect theFigure 1 Pigmented colonies of microorganismsin binder-free wheat-based plant plastic after 21 daysof exposure in active soilFigure 2 Changes in physical and mechanical properties of binder-free wood and plant plastics before and after biodegradationin active soil391237928977437438743945104263162692572010 74103 8 3020406080100BF-WP beforebiodegradationBF-WP afterbiodegradationBF-PP-wheatbeforeBF-PP-wheat afterbiodegradationBF-PP-milletbeforebiodegradationBF-PP-millet afterbiodegradationbiodegradationHardness, MPaCompression elasticity modulus, MPa X 10–1Elasticity number, %Breaking stress, MPa151Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154material from biodegradation, improve its biostability,and reduce its biodegradation potential. The samples’physical and mechanical properties were analyzedbefore and after biostability tests. We found that theseproperties were affected by the type and method ofantiseptic administration.The BF-WP samples had the worst indicatorswhen a water repellent was introduced directly intothe press material. In particular, there was an averagedecrease in flexural strength by 49%, hardness by 14%,water absorption by 30% (after 24 h), and swellingin thickness by 1.5% (after 24 h).This might be explained by the disturbed formationof supramolecular bonds between the mixture particlesduring pressing. Lignin was present in the liquid phaseof the mixture and the water repellent distributed iton the surface of the particles, providing them withhydrophobic properties. Thus, this modification becamea structural and mechanical factor that interfered intothe formation of bonds between the particles. However,when applied to the surface of the BF-WP samples, thewater repellent improved their physical and mechanicalproperties by an average of 1–10%.The best indicators were found in those BF-WPsamples which were protected with copper sulfateintroduced into the press material. They had the highestvalues of hardness, compression elasticity modulus, andbreaking stress compared to all the other experimental(protected) and control (unprotected) samples.A similar picture was observed in the binderfreeplant plastics. Introduced into the press mixture,the water repellant caused a sharp deterioration inflexural strength and water absorption (by 10 and 11%,respectively). When applied to the surface, it improvedthese properties by 10 and 14%, respectively. Coppersulfate that was introduced directly into the pressmixture increased the strength indicators (flexuralstrength by 14%, hardness by 49%), but reduced waterresistance (water absorption rose by 23% and swellingby 28%). These effects must be taken into account whenformulating binder-free, antiseptically protected plasticsbased on wood and plant materials.The experimental BF-WP and BF-PP sampleswere exposed in active soil for 21 days and then testedfor biostability. Our analysis of the physical andmechanical properties of the control (unprotected) andexperimental BF-WP samples showed a significantdecrease in strength indicators. The greatest decreasein flexural strength (by 39%) was found in the controls.This indicator fell by 29% in the samples treated withTable 1 Physical and mechanical properties of binder-free wood plastics protected with antiseptic coating (biostability tests)Physical and mechanical properties Control Antiseptic coatingWater repellent Copper sulfate Forwood antisepticWeek Week Week Week1 2 3 1 2 3 1 2 3 1 2 3Flexural strength, MPа 3.4 2.6 2.0 3.5 2.8 2.6 3.2 2.8 2.7 3.2 2.3 2.2Hardness, МPа 8.6 8.6 8.6 17.2 9.1 9.0 9.0 8.8 8.9 9.2 9.0 8.9Elasticity number, % 40 39 39 65 38 37 41 41 41 51 42 37Compression elasticity modulus, МPа 62 58 58 156 64 63 63 61 61 64 62 62Breaking stress, МPа 6.4 6.4 6.4 12.3 6.8 6.7 6.7 6.6 6.7 6.8 6.7 6.7Yield stress, МPа 2.6 2.6 2.6 4.9 2.7 2.7 2.7 2.6 2.7 2.7 2.7 2.7Water absorption in 24 h, % 82 82 95 49 55 56 67 72 71 54 76 84Swelling in thickness in 24 h, % 6.1 6.8 8.4 3.7 6.5 7.5 5.5 7.0 7.4 5.6 7.6 8.1Table 2 Physical and mechanical properties of binder-free wood plastics protected with an antiseptic introduced into the pressmixture (biostability tests)Physical and mechanical properties Control Antiseptic introduced into the press mixtureWater repellent Copper sulfateWeek Week Week1 2 3 1 2 3 1 2 3Flexural strength, MPа 3.4 2.6 2.0 1.1 1.1 0.8 4.7 3.9 3.7Hardness, МPа 8.6 8.6 8.6 8.9 8.4 8.4 16.2 14.1 10.3Elasticity number, % 40 39 39 50 45 41 48 34 33Compression elasticity modulus, МPа 62 58 58 61 57 57 146 121 76Breaking stress, МPа 6.4 6.4 6.4 6.6 6.3 6.3 11.5 10.1 7.6Yield stress, МPа 2.6 2.6 2.6 2.7 2.5 2.5 4.6 4.1 3.1Water absorption in 24 h, % 82 82 95 110 115 115 44 47 51Swelling in thickness in 24 h, % 6.1 6.8 8.4 7.5 7.7 9.8 4.2 4.5 4.5152Buryndin V.G. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 148–154the Forwood antiseptic and by 26% in the samples witha water repellent introduced into the press mixture(Tables 1 and 2).Flexural strength had the smallest losses in thesamples protected with copper sulfate, namely 15%for the coated sample and 21% for the sample with amodified press mixture.Hardness was the highest in the wood plasticstreated with the water repellent and those with thecopper sulfate-modified press mixture, namely 17.2 and16.2 MPa, respectively, on the eighth day of exposure inactive soil. However, it was these samples that had thegreatest loss of hardness by the end of the biostabilitytest, by 48 and 36%, respectively. Yet, this indicatorremained the highest in the samples with added coppersulfate (10.3 MPa).Water absorption had the highest values in thesamples with an added water repellant, averaging 115%after three weeks of exposure. The lowest values were inthe samples with added copper sulfate, namely 51% bythe end of the tests (a loss of 16%).The plant plastics also showed changes in theirphysical and mechanical parameters. The smallest loss(24%) of flexural strength over three weeks of exposurein active soil was found in the samples with an addedwater repellent, although they had one of the lowestvalues (0.4 MPa) in the first week. On the eighth day,this indicator was the highest in the samples coatedwith a water repellent (2.5 MPa), decreasing by 53% to1.1 MPa by the end of the test (Table 3). The hardnessindicator decreased in all the plant samples within threeweeks of exposure in the range of 1–6%.Daily water absorption was the highest in thesamples with an added water repellent, amounting to228% after three weeks of exposure in active soil, witha 42% decrease of water absorption. By the end of thebiostability tests, the lowest water absorption was in thesamples coated with the Forwood antiseptic (122%).CONCLUSIONOur study showed high biodegradation andlow biostability of the binder-free wood and plantplastics based on sawdust, and wheat and millethusks. Therefore, antiseptic protection is requiredto improve their performance. Their exposure in abioactive environment caused some morphological andstructural changes, as well as affected their physical andmechanical properties.We found that the plant-based plastics underwenta more pronounced degradation in active soil than thesawdust-based plastics. According to our results, thesamples’ resistance to biodegradation was determinedby such process parameters as the type of fillerTable 3 Physical and mechanical properties of binder-free plant plastics protected with antiseptic coating (biostability tests)Physical and mechanical properties Control Antiseptic coatingWater repellent Copper sulfate Commercial antisepticWeek Week Week Week1 2 3 1 2 3 1 2 3 1 2 3Flexural strength, MPа 2.0 1.8 1.3 2.5 1.7 1.1 2.1 2.0 1.6 1.6 1.2 1.0Hardness, МPа 8.7 8.7 8.3 9.1 8.7 8.7 8.8 8.6 8.5 8.9 8.7 8.4Elasticity number, % 36 36 41 33 38 39 39 40 40 36 38 40Compression elasticity modulus, МPа 60 59 56 64 60 59 60 59 58 62 60 57Breaking stress, МPа 6.5 6.4 6.2 6.8 6.5 6.5 6.6 6.4 6.4 6.7 6.5 6.3Yield stress, МPа 2.6 2.6 2.5 2.7 2.6 2.6 2.6 2.6 2.6 2.7 2.6 2.5Water absorption in 24 h, % 89 113 158 90 121 151 103 119 151 88 101 122Swelling in thickness in 24 h, % 7.5 7.9 9.6 5.2 5.7 7.8 5.2 6.0 7.5 7.4 7.5 7.9Table 4 Physical and mechanical properties of binder-free plant plastics protected with an antiseptic introduced into the pressmixture (biostability tests)Physical and mechanical properties Control Antiseptic introduced into the press mixtureWater repellent Copper sulfateWeek Week Week1 2 3 1 2 3 1 2 3Flexural strength, MPа 2.0 1.8 1.3 0.4 0.3 0.3 2.0 0.6 0.3Hardness, МPа 8.7 8.7 8.3 8.9 8.9 8.9 8.9 8.8 8.7Elasticity number, % 36 36 41 37 38 38 34 38 38Compression elasticity modulus, МPа 60 59 56 62 61 61 62 60 60Breaking stress, МPа 6.5 6.4 6.2 6.7 6.6 6.6 6.7 6.6 6.5Yield stress, МPа 2.6 2.6 2.5 2.7 2.7 2.7 2.7 2.6 2.6Water absorption in 24 h, % 89 113 158 161 203 228 135 135 171Swelling in thickness in 24 h, % 7.5 7.9 9.6 5.1 5.2 5.3 5.3 5.4 5.6153Buryndin V.G. et al. 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Polymer Degradation and Stability. 2018;158:52–63. https://doi.org/10.1016/j.polymdegradstab.2018.10.023.15. Buryndin VG, Artyomov AV, Savinovskih AV, Shkuro AE, Krivonogov PS. The influence of temperature andtime on the performance properties of wood plastics without using resins. Systems. Methods. Technologies.2018;37(1):121–125. (In Russ.). https://doi.org/10.18324/2077-5415-2018-1-121-125.and antiseptic, as well as the method of antisepticadministration.We treated the plastics with three types of antiseptic(water repellent, copper sulfate, and Forwood) byadding them to the press mixture or applying them tothe surface. Both methods changed the initial propertiesof the samples. When used as a coating, the waterrepellent improved the samples’ physical and mechanicalproperties. When added to the press mixture, however,it significantly impaired their strength and waterresistance.Copper sulfate showed the best effect amongthose antiseptics introduced into the press mixture. Itdecreased the flexural strength of the sawdust-basedsamples by 5% and increased their hardness, waterabsorption, and swelling. The plant-based samples withadded copper sulfate showed better strength indicators,but lower water resistance. Thus, the antiseptic treatmentof binder-free plastics based on wood or plants affects anumber of their key physical and mechanical propertiesand should be administered with regard to expectedperformance conditions.CONTRIBUTIONAll the authors were equally involved in developingthe research concept, obtaining and analyzing the data,and writing the manuscript.CONFLICT OF INTERESTThe authors declare that there is no conflict ofinterest.