Technical field

The invention relates to materials degrading in soil, specifically the invention relates to a method for preparation of a mass with wood ash and binder as clay and optional additional binders, which is biodegradable in soil, and a biodegradable container made of the mass.

Prior art

Wood ash is a solid residue of wood combustion, consisting of a mineral (predominant) and organic (marginal share) part. The wood ash content accounts for approx. 1-3% of the dry biomass weight. Bark increases the average ash content, with ash content accounting for 3-4% of dry bark weight. The properties of ash are mostly affected by the combustion temperature of wood in the furnace. Wood ash is a fine-grained material, where the particle size is similar to the size of clay (< 0.01 mm) and dust particles (0.002-0.05 mm). The average density of wood ash is 0.27- 0.67 g/cm ³ , dry matter content > 99%, pH > 12. The mineral part of wood ash is formed by amorphous, semi-crystalline and crystalline components and the organic part by biologically stable charcoal and organic minerals, which occur in the ash in case of incomplete combustion of the fuel. From horticultural aspect, wood ash is valuable mostly due to the content of P, Ca, Mg and K. Plants can absorb the nutrients contained in ash, wherefore ash is used in agriculture, gardening and forestry. For example, field and greenhouse tests conducted with wood ash have shown that ash, delivered with the rate of up to 50 t/ha, is a suitable fertilizer for many plant species. See "Wood ash valorization as functional fertilizers in agri- and horticulture", Environmental Investment Centre Project No. 10053 report, Estonian University of Life Sciences, Tartu 2016, https://www.kik.ee/sites/default/files/uuringud/kik_10053_ar uanne-05.07.16.pdf.

Clay is a sedimentary rock, where the diameter of particles (clay minerals) is 0.005- 0.0002 mm and the number of such particles in one cubic meter is approximately one trillion. Clay can be used as a binder. Known are biodegradable planting pots of natural cellulose, in paper package, and coconut coir pots. Known are also planting pots http://ee.china-bamboo- products.in/bamboo-gardening/bamboo-fiber-plant-pot/trendy-b iodegradable- planters-pots.html, which are produced from natural plant fibres (rice hulls, rice stalks, wheat straw, corn stalks and bamboo fillings or natural bamboo fibres and rice husks). No wood ash is used here.

Known is a biodegradable flower pot (KR201 10015487, Seo Jung Soo, published February 16, 201 1 ), where natural by-products are used and a method is provided, which foresees the use of biodegradable materials, including food waste and agricultural by-products, in producing the flower pot. The method for the preparation of biodegradable flower pot comprises the following stages: crushing and grinding of natural by-products (such as sorghum, grass seeds, rice, barley, soyabean, wheat grain, rice straw, barley straw, grass, corn stems, cane, weed, manure), adding starch, yellow soil and clay to the mixture, the mixture is heated under pressure and moulded under pressure into a flower pot, the moulded flower pot is dried and coated with waterproof plant paint. No wood ash is used in this solution.

Known is an urn (JPH1 1 178868, Sasaki Nobumasa, published July 06, 1999), which is produced from a material that does not pollute the environment and degrades over time in a natural environment. Wood, wood powder, biodegradable plastic or natural ores could be used as the material. The urn together with the ash degrade through the action of micro-organisms in the soil. No clay is used in this solution.

Known is a method for the preparation of biodegradable containers (EP1327663, New Ice Ltd, published July 16, 2003), which comprises the stages: forming a pre-gelled starch suspension, adding to this wood fibre and wood powder, to which clay, ash, water, unmodified starch are added selectively, to create a homogeneous mouldable composition mixture, the homogeneous composition is formed with heat and heat/pressure, to produce the biodegradable container. A disadvantage of this solution is the method, which is more complex and more expensive, because other substances in addition to clay and ash are used for the preparation of the composition mixture and the biodegradable container is moulded with heat/pressure. Summary of the invention

The purpose of the invention is to present a method for the preparation of a biodegradable mass, which comprises wood ash and clay as a binder or another additional natural binder as an additive, to prepare a single-use container that biodegrades in soil.

The method for the preparation of the biodegradable mass of wood ash and clay comprises the following stages: the mass is obtained by mixing fine-grained wood ash and clay as a binder, while ash content in the mass accounts for 55-65% and clay content 45-35%; the mass is given a form and air-dried in a gypsum mould, while the used mass is fresh; the formed container is removed from the mould and is dipped in water; the container that has been dipped in water is dried in the air. Prior to placing into the mould, the mass is rolled in dry wood ash. The wood ash is ash combusted from wood chips from forestry and the clay is Cambrian blue clay of Kunda. A natural binder is used as an additional binder, selected from among bentonite, gypsum, cement, dolomite or sawdust.

The biodegradable container produced with the presented method comprises wood ash 55-65% and clay 45-35%, while the wood ash is ash combusted from wood chips from forestry, sieved to particles size 1 mm and the clay is Cambrian blue clay of Kunda. The biodegradable container is a planting pot or a burial urn.

Embodiment of the invention

The biodegradable mass obtained with the method of the invention comprises wood ash, which is preferably the residual product obtained with the combustion of woodchips in the central heating wood furnace with a grate, bound together with clay, which is preferably the Cambrian blue clay of Kunda. The ash does not stay together without the additive(s).

The wood chips used are preferably wood chips from forestry, including both wood and bark.

Other natural binders can also be used in addition to clay. The preferable binder to be used is the Cambrian blue clay of Kunda, which belongs in the group of low-melting clays of medium plasticity. The clay is a bluish green sedimentary rock with the smallest particles, the diameter of the particles is a thousandth of millimetre, predominantly 0.005-0.0002 mm. There are approximately one trillion particles in one cubic centimetre. At this, the clay particles are not a mechanically ground powder of our regular minerals (quartz, feldspar and other additives), but clay minerals. The drying shrinkage of the clay is 7-8%.

The obtained mass is used to prepare a single-use container, which remains stable in normal use and is biodegradable in soil. In preferred embodiments, the container is a planting pot or a burying urn. The preferable maximum capacity of the container is 3 litres, it remains stable with short-term exposure to water (either immersed once or for 1-3 days, if additional binders are used) and preferably biodegrades in soil in 3-7 years. In a mould, the mass is formed into a container with the required shape. The mould is preferably a gypsum mould, but melds of other materials (such as plastic, bioplastic, silicone, paper or another fibre) may also be used.

The preferable ratio of ash and clay in the mass in per cents is 55-65% of ash: 45- 35% of clay. The additional binder is optional and forms a marginal part of the whole mass. The desirable ratio of ash and clay in the mass depends on the composition of the ash. The more ash in the mass, the longer stability of unfired mass exposed to water. The more clay in the mass, the faster the container degrades in case of exposure to water. The physical properties of the container are also dependent on the ash used, for example, containers prepared with the same recipe, using lighter ash, are more durable than containers of darker ash. Since each batch of ash is different, a sample must be prepared of each ash batch for the production of containers. The content of ash in the mass should exceed the mass of clay and additional binder, to make sure that unfired mass (fresh mass) would remain stable sufficiently long in case of exposure to water (for example, after dipping in water once or immersion for a short period).

The wood ash has been sieved previously (preferably to maximum particle size of 1 mm). The finer the sieve, the better the ash remains together, and the more there are additional particles in the ash, the more brittle is the form made from the ash. The clay provides the container with the necessary plasticity and allows the ash to stay together.

Optionally, other additional binders may be used in addition to clay. Such additional binders could be, for example, bentonite, gypsum, cement, dolomite, sawdust. Bentonite, for instance, increases the elasticity of the mass, but reduces the stability of the container in exposure to water. Some additional binders increase the durability and stability of the container, but elongate the production process of the container (longer drying time).

In the preferred embodiment, the mass comprises only wood ash and clay, most preferably the Cambrian blue clay of Kunda.

The container is preferably produced from fresh mass (no post-baking). In order to avoid immediate degradation of the container produced from a fresh mass in a mould, the container is briefly dipped in water and dried, thereby making the container more durable and more stable when exposed to water.

The method for the preparation of biodegradable mass and production of a biodegradable container from the mass comprises the following stages: wood ash and clay or another additional natural binder is mixed to achieve a plastic and mouldable mass; the mass is placed in a mould; the mass is air-dried in the mould; the mass is removed from the mould and a container is achieved; the container is immersed in water and dried in air.

The method is executed by first preparing the mass for which fine-grained and sieved wood ash and clay are mixed in a mixer (until the mixture becomes plastic and mouldable) in the following ratio by per cent: ash 55-65%, clay 45-35%. The resulting mass stays well together, has good moldability, durability, sufficient stability in exposure to water, and the mass is fresh, i.e. without additional firing.

The mass is formed into a container in a gypsum mould. Before placing into the gypsum mould, the mass is preferably rolled in dry wood ash, facilitating removal of the container from the gypsum mould. The mass is air-dried inside the mould, then the formed container is removed from the mould, is briefly dipped in water (preferably at room temperature) and dried in the air preferably for approximately 160 hours.

The embodiment of the invention proceeds from the premise that the weight of the ashes to be used varies, and therefore the weight of the components used in the tests were selected in the ranges: ash 45-80% and clay 20-55%. Masses, where the ash content was > 65% and < 55% proved to be the weakest. Tests also showed that the more ash in the ash and clay mixture, the longer the stability of the unfired mass in water. Therefore, the recipe of the most durable ash and clay mass is: ash 55-65% and clay 45-35%.

The produced container is intended for single-use and is stable in conventional use, but has reduced stability when placed in soil and degrades (biodegrades) completely over time (preferably in 3-7 years). Preferably, the container is a planting pot and burying urn. As a planting pot, the container also functions as a source of additional fertiliser.