Introduction
Over 67 million tons of packaging wastes are generated annually in the EU, containing up to 30% of slowly degrading plastics. The Packaging and Packaging Waste Directive, which standardizes the production of packaging materials, waste management and the use of recycling, composting, and energy recovery by incineration regulates the bio-based packing sector (European Parliament and Council Directive
1994). There are clear targets regarding waste reduction in the EU. Seventy-five percent of packaging waste should be recycled by 2030 (Niero and Hauschild
2017). Re-utilization of waste paper is therefore important for reducing waste generation but also for saving wood resources (Kose et al.
2016). According to Chartered Institution of Waste Management, the reduction of waste quantity might save 72 billion € per year and create over 400,000 new jobs in Europe (Cheshire
2016).
The increased use of bio-based materials is essential in order to reduce the environmental impact of materials, including reuse and ultimately, disposal. It is expected that use of biodegradable materials will contribute to sustainability and reduction in the environmental impact associated with disposal costs (Song et al.
2009). Moreover, increased bio-based material use is in line with Circular Economy (CE) objectives, which aims to maximize value at each point in a product’s life by keeping products, components and materials at their highest utility at all times (Stahel
2016).
Currently, landfilling is the dominant method of packaging waste disposal, followed by recycling, incineration, and composting (Valdés et al.
2014). However, it is considered as “leakage” from circular system, meaning that valuable resources are wasted and lost from environmental and economical point of view (Cheshire
2016). The most favorable way for transformation of ligno-cellulosic wastes is by recycling. The feasibility of recycled fibers for the production of high value-added papers to be used for packaging purposes was recently reported by Tarrés et al. (
2018). However, fibres recovered from paper wastes after re-pulping process have reduced mechanical properties. According to Wistara and Young (
1999) tensile strength, bursting strength, and apparent density of the pulps decreases when recycling paper. After a maximum of 6–7 recycling cycles, fibres become too short for further processing. Consequently, additives (new fibres or fillers) are necessary to enrich recycled pulp and to minimize depreciation of its quality (Villanueva and Wenzel
2007). In some circumstances increased use of fillers leads to decrease paper strength (Balea et al.
2018). Moreover, physical recycling may be impractical in case of packaging materials contaminated with foods or other biological substances (Kale et al.
2007). Composting paper waste is considered as one of the less costly disposal routes, and is an option for recycling (López Alvarez et al.
2009). In this scenario, biodegradability becomes a desirable feature for several everyday products, including packaging. Although ultimate biodegradability in the natural environment is important, sustainable packaging products are required to biodegrade in a controlled and industrially acceptable way (Scott and Wiles
2001). However, the main factor that affects the formation and manufacturing of bio-based packaging is related to economic aspects.
Biodegradable pots, developed as an alternative for traditional petroleum derived plastic containers are environmentally friendly and frequently used for silvicultural and agricultural purposes. Such containers reduce overall costs, as seedlings with the bio-degradable pots can be planted quickly while avoiding root disturbance or any interruption to plant growth. 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 mechanically 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 alternatives, 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 becoming attractive fibre reinforcement solutions for bio-composites (Ochi
2011; Schettini et al.
2013; Nambuthiri et al.
2015; Tesfaye et al.
2017). Substances from plant waste materials (such as: cellulose, hemicellulose, 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 (Müller et al.
2007). A solution that fulfils both of these requirements 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 commercially available cellulosic fillers and could be successfully 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 various 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, López Alvarez et al. (
2009) have emphasized 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 alternative 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. Moreover, 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 favourable 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.
The goal of this work is to increase the positive footprint of packaging products by designing “eco-effective” solutions according to the Cradle to Cradle design framework. Reutilization of two kinds of materials (waste paper and cereal bran) is proposed here in order to close the loop at the end of product life cycle. The aim was to design, manufacture and examine the degradation intensity of waste papers containing cereal bran with a special focus on the effect of the soil type. Both, paper sheets and paper pots were evaluated. It is expected that by understanding the degradation rate of the investigated products it will be possible to optimize paper pots manufacturing to assure sufficient mechanical resistance and the desired rate of degradation.
Conclusions
The cereal bran used in this experiment was characterized by a relatively high starch content. Starch promotes the binding of natural fibres during paper manufacturing and consequently improves the paper strength. Mechanical properties are particularly important in the production and utilization of paper pots manufactured from recycled fibres. The addition of cereal bran improved the mechanical properties of paper products tested in this study; paper pots with bran fillers were less susceptible to mechanical damage, when compare with commercial products. The biodegradation rate of pots changes with the quantity of added bran. Biodegradation in these pots is generally slower than in commercial pots containing peat, but faster than in pots without fillers.
It was concluded that the extent of decomposition does not extensively depend on the type of filling (rye or wheat cereal bran), but rather on the quantity of filler added, exposure time and soil type. Depending on the soil type, water holding capacity and pH, soil may stimulate or inhibit the growth of microorganisms responsible for the decomposition of paper products. Paper samples (both sheets and pots) in all tested configurations degraded most rapidly in agricultural and forest soils, while biodegradation proceeded slowly in the sand soil.
Analysis of NIR spectra revealed that the most advanced degradation occurred in agricultural soil. The organic content accelerated the degradation rate within all investigated papers. In contrast, sandy soil, which is low in organic matter, resulted in the lowest degradation rate and inhibited degradation processes.
All tested paper configurations could be suitable for manufacturing plantable bio-containers that will slowly disintegrate during their lifespan. Their use improves both the sustainability and public perception of the investigated products. However, in addition to environmental and economic aspects, the effect of alternative containers on plant growth and quality should be considered. Therefore, our future work will be related to calculation of environmental impact of manufactured paper packaging products. Proper use of the experimental results may help in selection of products with optimal composition for specific applications, including pots used in horticulture or for forest nurseries. Moreover, by proper fillers selection, packaging products with custom degradation rate best suited to certain crop cycle durations and adopted for specific types of soils may be designed.
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