Cellulose
The most commonly used disposable pots are made of peat or a mixture of peat with wood fibres. Such pots can be easily embedded into the soil with plants or converted into bio-gas (digested) after removing the plant. On the other hand, such containers are mechan- ically unstable and possess high permeability to water vapour. Salt deposition on pot walls is frequently observed and causing nutrient content to become unavailable. This may have a negative impact on plant production and therefore horticulturalists are not always confident to use pots made of peat (Treinyte et al. 2014). Moreover, some consumers avoid the use of peat because peat harvesting may be unsustainable and possibly contribute to global climate change (Mitsch et al. 2013). Containers produced from coconut fibres or bird feathers are interesting alterna- tives, as these are mechanically more resistant and retain moisture well. However, these cannot be embedded in soil with plants and can only be disposed or digested afterward (Treinyte et al. 2014). Recycled plastic geotextiles are other option recently introduced to the market. These are not easily biodegradable or compostable, but will slowly disintegrate when exposed to the soil. A common limitation of these products is their relatively high price, therefore continuous research regarding development of novel packaging products is ongoing. Natural fibres and agricultural residues are becom- ing attractive fibre reinforcement solutions for bio- composites (Ochi 2011; Schettini et al. 2013; Nam- buthiri et al. 2015; Tesfaye et al. 2017). Substances from plant waste materials (such as: cellulose, hemi- cellulose, starch, dextrin, and other carbohydrate polymers) are the most convenient solution as they solve two problems simultaneously: they contribute to efficient waste management and avoid or minimize the use of chemical additives as binders (Mu¨ller et al. 2007). A solution that fulfils both of these require- ments is cereal bran. In typical flour production processes, cereal bran is devoid of nutrients, and is most often separated for disposal, leading to handling, storage and disposal costs. According to Formela et al. (2016) bran are interesting alternative for commer- cially available cellulosic fillers and could be success- fully applied as a low-cost filler in polymer composites. Therefore, bran may be an ideal filler for the extruded paper or pulp containers used extensively in horticulture. It may also serve as an
inhibitor controlling the bio-degradation rate in var- ious products (Sandak et al. 2011). Evaluation of paper products decomposition in laboratory conditions with selected microorganisms was previously reported (Modzelewska et al. 2010; Jaszczur and Modzelewska 2011; Sandak et al. 2015). However, Lo´pez Alvarez et al. (2009) have empha- sized the necessity to establish biodegradation curves for different packaging products in landfill and/or composting end-of-life scenarios. Such experiments conducted in different soil types and climates are essential before adopting containers made with alter- native materials. It is important to note that the same physical characteristics that promote degradation during composting could also contribute to premature degradation during production and transportation. Depending on their capacity to degrade at their end- of-life, alternative containers are usually classified as plantable, compostable or recyclable (Nambuthiri et al. 2015). Various types of soil have different influence on degradation rates mainly due to variability in water- holding capacity (Rahman and Chattopadhyay 2007), available nitrogen, pH, presence of microorganisms and organic matter content (Nambuthiri et al. 2015). In soil with neutral or slightly acid pH (6.0–7.0), favourable microorganisms and minerals necessary for plant roots are present (Yeomans 1954). Such beneficial bacteria are not present in more acidic soils, leading to uncontrolled mould fungi growth. More- over, most of minerals are insoluble in soils possessing low pH. Sandy soil is airy and highly permeable. It has rather low water storage capacity, is fast drying and easily loses nutrients due to leaching. In practical applications, it can be improved by adding organic matter or fertilizers. Soil present in coniferous forests contain litter compost composed primarily of pine or spruce needles, ericaceous understorey plant species and mosses (Hilli et al. 2010). The compost is highly acidic but has good leavening properties and can be used as an optimal peat substitute providing favour- able conditions for plant growth (Drozd et al. 2002). Recycled paper containers have been proven to have the comparable wet and dry vertical and lateral strength, similar to those of plastic containers, and showed no algal or fungal growth on the container wall (Nambuthiri et al. 2015). However, additives and fillers might influence the performance of packaging products.
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