*3.2. Technical Characterization*

The Bio-flexi panel was extruded using a double-screw extrusion machine, in which four heating canals existed to control heating temperatures throughout the longitudinal mixing path of the compounded mixture. At the heating canals as well as the feeding canal, gas absorbers were integrated to absorb water vapor arising from the natural fibers, which previously captured natural atmospheric humidity to optimize the mixture and eliminate any inhomogeneity or plasticity (Figure 4).

**Figure 4.** Illustration of the production of Bio-flexi in mass-production scale indicating the control and feeding units in Naftex GmbH company, Wiesmoor, Germany (Photo: Dahy, H.).

The developed Bio-flexi HDF product was mechanically tested to evaluate the transportation safety without distortion and the usage possibility in flooring systems in respect to residual indentation after DIN EN 433 and indentation resistance after DIN EN 1516, to evaluate if the product can be applied in the scope of flat flooring in sport halls [92]. To validate the possibility of applying this material in flooring systems, the fiberboard was tested under static loads to measure thickness losses, as a step to measure its residual indentation and indentation resistance. Measurement of residual indentation after DIN EN 433 simulates the static furniture loads. The result indicated that Bio-flexi at 80% fiber-load by mass has a residual indentation of 0.14 mm, which is comparable with other elastic flooring materials as Linoleum that lies between 0.07–0.4 mm. To validate the resistance to indentation of elastic surfaces for sport areas, DIN EN 1516 test standards were applied to determine that the permanent change in the flooring plate thickness was only 0.02 mm that fits in the range set in this standard not exceeding 0.5 mm permanent thickness loss. This indicates that the developed fiberboard can be applied in flooring systems in sport halls, sport activity areas and in cushioning services [91].

Under the raising awareness of the environmental possible drawbacks of all newly developed building materials, thermoset matrix application was eliminated here and a thermoplastic elastomeric binder (TPE) was applied instead. Recyclability is here guaranteed without further experimental proof dependent on the thermoplasticity of the binder and the high heat-resistance of the natural fibers reaching to 220 ◦C depending on the flame-resistant silica loaded contents, which should enable multiple recycling cycles before the fiber deteriorates. However, in the area of Natural Fiber Reinforced Polymer Composites (NFRP) recycling virgin thermoplastic binders of the same or another compatible base as well as virgin natural fibers are needed to be added in small ratios in each recycling cycle to guarantee preserving the same original quality of the first produced series. The composting option was otherwise experimentally proved through soil burial tests that were conducted for 15 months, where the samples were buried in a chosen field plot in the middle of the Stuttgart city in South Germany. Compostability conditions were set so that aerobic bacteria at a level of maximum −8 cm under the soil's surface were activated, to measure if or not the test samples will start decaying. Weight reduction was monitored and visual qualitative inspection took place each 3 months. By the end of the test, plant roots were observed growing within the samples' bodies and a final weight reduction of around 41% after 15 months of soil burial were measured. Through these results, it was concluded that the Bio-flexi fiberboard has also the tendency to be industrially composted as a second end-of life option in addition to its recyclability. In Figure 5, the closed cycle graph of the Bio-flexi according to the cradle to cradle® design conception is shown including the two main product circles that are impacted by the Bio-flexi life cycle.

**Figure 5.** Graph indicating the closed proposed cycle of the Bio-flexi HDF fiberboard after the cradle to cradle® concept (Photo: Dahy, H.).

#### *3.3. Bio-Inspired Sustainability of Bio-Flexi*

The assessment of Bio-flexi is performed based on a system model that has been created in analogy to the Life Cycle Inventory model in LCA. For the modelling, the LCA software GaBi was used [56]. In analogy to LCA, the goal and scope definitions are presented in the following. Goal of the assessment is to investigate the sustainability of Bio-flexi in a sports facility flooring application compared to a conventional reference system, for which a polyurethane based flooring material is chosen. One square meter of flooring material is chosen as functional unit. As the complementing build up is assumed to be similar for both systems, the comparison is restricted to these surface layer materials, also providing the basic functions of shock absorption and cushioning in a comparable way. The service life is defined as 20 years and no difference in maintenance is considered.

The technical characterization has been transferred to a Life Cycle Inventory model using primary data provided by the manufacturers including the life cycle phases A1–A3, C3 and D [93]. As the technology provides two EoL-options, a sensitivity analysis has been conducted, resulting in two

different scenarios that depict the most realistic options. Scenario one is using a maximum amount of recycling and scenario two is treated through composting. In addition to the information given in the technical characterization, several additional processes were added to complement the life cycle with regard to recycling and composting. For the recycling option a grinding process has been applied to facilitate the recirculation of recyclate to the virgin raw material stream before the extrusion process takes place. A percentage of 20% was specified as maximum recyclate rate. For the composting option, an industrial composting plant model was chosen to estimate the according material decomposition rate in real application. As coarse material is removed showing a relatively low decomposition rate due to its small surface area, a grinding process is assumed here as well. For the remaining materials thermal utilization is assumed, using a dynamic energy mix based on German lead scenarios to calculate the benefits beyond system boundary [56]. The system boundary of the two scenarios is shown in Figure 6.

**Figure 6.** System boundary of the investigated life cycle inventory model. The main material and energy flows for production, End-of-Life and Benefits are shown. The recyclate preparation is only considered for the recycled scenario and therefore depicted separately.

The model was used as basis to perform a BiSA according to the assessment structure described above. As there is no decidedly specified environmental function, the environmental function is not investigated. For the economic assessment, a simplified approach is chosen due to the fact that Bio-flexi is still a product under development and a number of non-material information is not ye<sup>t</sup> available. The social function in terms of building physical design functions is assumed to be comparable to the conventional reference product as indicated by divers tests [91]. In the following, the aspect environmental burden is presented in detail due to its relevance related to the motivation of the developers. Figure 7 depicts the overall environmental burden in normalized numbers, showing the overall environmental impact with regard to the planetary boundaries.

While the impact of the most relevant category for PUR is strongly reduced in both Bio-flexi scenarios, the overall impacts of all categories are almost compensating these savings for the recycled scenario and even overcompensating the savings for the composted scenario, having an increased in normalized impact by 17%. The increased impact mainly origins in the agricultural system, which especially impacts on eutrophication and acidification. Overall, the recycling option already is

comparable to the reference system and offers further saving potential especially when the recycling rate can be further improved.

**Figure 7.** Environmental burden of the reference system and the two scenarios of Bio-flexi (Recycled and composted) as normalized results for the considered life cycle phases.

The overall sustainability assessment result is depicted in Figure 8. The segments are scaled in relation to the reference system using the radius as scaling element. Diagram (1) shows the recycled scenario, diagram (2) on the right hand side depicts the composted scenario. While for both economic and environmental burden only small changes can be identified, the social burden offers significant savings for both scenarios.

**Figure 8.** Bio-inspired sustainability of Bio-flexi as pie charts, including the six aspects of sustainability, each depicted by a specific color. The red elements depict the social aspects, the blue elements depict the economic aspects and the green element depicts the environmental aspects. As there is no environmental function of both reference and assessed system, the environmental function element is greyed out. Each aspect is shown in relation to the reference product, depicted by a grey circle line which is identical for both graphs. The relative value is depicted as change in pie element radius and therefore linear. (1) The recycled scenario shows Bio-flexi with a maximum of recycling compared to a conventional reference product. (2) The composted scenario shows Bio-flexi with a maximum of composting compared to a conventional reference product.

For both economic burden and function, the assessment was restricted to the process immanent cost model, where both scenarios provide a similar cost structure. The overall production costs

are furthermore comparable to the conventional flooring material. For social burdens, a significant reduction of the impact on human capability has been identified. This mainly origins in the fact that the Bio-flexi production including its upstream material chain takes place mainly in Germany, while the fossil based reference product includes significant share of work with higher risk of human capability reduction mainly in the raw material extracting countries. The impact on human health does not provide significant saving potentials for the composted scenario and is increased by 51% due to the impacts occurring in the composting process. For the recycled scenario, a reduction of 25% of normalized impact in comparison to the reference system is determined. Overall, the recycled scenario offers a higher potential with regard to bio-inspired sustainability, although this does not apply to each aspect concurrently. The main improvement could be identified in the reduction of social burdens and global warming potential, while no significant change could be identified for economic aspects for both function and burden.

The biobased and biodegradable composite Bio-flexi appears to be able to compete in terms of bio-inspired sustainability with its conventional, fossil-based reference in the application as flooring system in sports facilities. In contrast to the reference, however, Bio-flexi bears several additional optimization potentials and is expected to be generally beneficial when further developed under consideration of the decision support provided by the BiSA system. Especially with regard to recyclability, improvement potentials have been identified, as the recycled Bio-flexi scenario provides significant improvements in environmental and social burden compared to both the reference system and the composted Bio-flexi scenario. While product development continues, economic function and burden assessment can be specified further, focusing on nonmaterial information. Nevertheless, the already competitive process immanent costs indicate potential profitability as cost reduction potentials are oftentimes identified in ongoing product development.
