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Life Cycle Assessment of Hemp Cultivation and Use of Hemp-Based Thermal Insulator Materials in Buildings Luca Zampori,* Giovanni Dotelli, and Valeria Vernelli Department of Chemistry, Materials, and Chemical Engineering “G. Natta”, Politecnico di Milano, INSTM RU-POLIMI p.zza L. da Vinci 32, 20133 Milano, Italy

Environ. Sci. Technol. 2013.47:7413-7420. Downloaded from pubs.acs.org by UNIV OF SOUTH DAKOTA on 08/27/18. For personal use only.

S Supporting Information *

ABSTRACT: The aim of this research is to assess the sustainability of a natural fiber, such as hemp (Cannabis sativa), and its use as thermal insulator for building applications. The sustainability of hemp was quantified by life cycle assessment (LCA) and particular attention was given to the amount of CO2eq of the whole process, and the indicator greenhouse gas protocol (GGP) was selected to quantify CO2eq emissions. In this study also CO2 uptake of hemp was considered. Two different allocation procedures (i.e., mass and economic) were adopted. Other indicators, such as Cumulative Energy Demand (CED) and EcoIndicator99 H were calculated. The production of 1 ha yielded 15 ton of hemp, whose global warming potential (GWP100) was equal to about −26.01 ton CO2eq: the amount allocated to the technical fiber (20% of the total amount of hemp biomass) was −5.52 ton CO2eq when mass allocation was used, and −5.54 ton CO2eq when economic allocation was applied. The sustainability for building applications was quantified by considering an insulation panel made by hemp fiber (85%) and polyester fiber (15%) in 1 m2 of wall having a thermal transmittance (U) equal to 0.2 W/m2_K. The environmental performances of the hemp-based panel were compared to those of a rockwool-based one.

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glass fibers,25−27 with the advantage of sensibly reducing composite density. So, what makes hemp highly suitable in building applications are primarily its good hygrothermal28,29 and maybe its acoustical insulation properties.30,31 In general, this material is well suited for different applications, such as outer coat, internal insulation of walls and roofs, insulation in the cavity, insulation for partition walls, roof insulation, isolation from foot traffic; as to the sustainable aspect, hemp fiber mat is biodegradable and retrievable. The combination of a panel of low density between the masonry and the plaster improves the thermal insulation as well as also the acoustic properties. Furthermore, panels do not oppose any resistance to water vapor: in case of condensation and infiltration hemp dries quickly and retains its properties.28 Besides thermal, mechanical, and acoustical properties, the use of natural fibers has a very high carbon storage potential, as demonstrated by Pervaiz and Sain32 who estimated a value of 325 kg of carbon stored per metric ton of hemp-based polypropylene composite. In addition, the net carbon sequestration by industrial hemp crop is estimated as 0.67 ton/ha (hectar)/year.32 For this reason, Vieira et al.33 evaluated the possibility of substituting eucalyptus tree with industrial hemp crop for pulp and paper production; a comparative

INTRODUCTION In recent years there has been an increasing interest of different industrial sectors in renewable raw materials of natural origin1−4 which are perceived as somewhat more sustainable than manmade products, as shown by different authors who investigated the industrial use of fibrous natural materials such as kenaf,5 sheep wool,6 hemp, and flax.7,8 In particular, the use of natural fibers seems to have mainly attracted the attention of two industrial sectors: One is the field of polymer-matrix composites,9,10 where natural fibers are used as reinforcements thanks to their potentially very high Young modulus,2 and the other is the building sector,11 where they are gaining increasing popularity for insulation purposes, because of their thermal characteristics and sustainability.12,13 Among others, hemp fibers are more rapidly widening their field of application in the building industry,14−18 even though researchers such as de Brujin et al.19 have shown that mechanical characteristics of hemp containing bricks (the so-called hemp-concrete) are not adequate for them to be used as load-bearing materials; it is only by relaxing thermal insulating properties and increasing the binder amount that mechanical strength of these blocks can raise,20 although other factors, such as chemical pretreatment on fibers21 and curing conditions,22 compactness during casting23,24 may have strong effects on hemp-concrete mechanical properties. Although lime is the most common binder used in hemp-concrete, there is also an interest in using hemp in fiber-reinforced cement composites in substitution of © 2013 American Chemical Society

Received: November 15, 2012 Accepted: June 10, 2013 Published: June 10, 2013 7413

dx.doi.org/10.1021/es401326a | Environ. Sci. Technol. 2013, 47, 7413−7420

Environmental Science & Technology

Article

LCA, in previous LCA studies of hemp fiber production7,35 the contribution of biogenic CO2 was not considered. Instead, the ISO 1406742 states that “where GHG (GreenHouse Gases) emissions and removals arising f rom the use stage or f rom the endof-life stage occur over more than ten years af ter the product has been brought into use, these GHG emissions and removals shall be included in the CFP (Carbon Footprint of Products) without the ef fect of timing of the GHG emissions and removals.” The assumption of a use phase longer than 10 years is the case of natural fibers used for building applications, such as insulating panels, so CO2 uptake should be entirely considered. In addition, the ISO 14067 at point 6.3.9.6 suggests “When CO2 is stored as carbon in a product for a specif ied time, this carbon storage shall be treated according to the provisions in 6.3.8. If any carbon storage in products is calculated, it shall be documented separately in the CFP study report but not included in the CFP. NOTE Carbon storage in products may also be provided for information when performing cradle-to-gate studies when this information is relevant for the remaining value chain.” So, in this paper the amount of biogenic carbon will be separately specified. The new release of the PAS 2050:2011,43 quite accordingly to ISO 14067, states that carbon storage should be included in a Carbon Footprint, only if storage actually occurs for over 100 years.

analysis of sustainability of the two options was carried out via LCA (life cycle assessment). Considering that hemp is an annual plant, which needs to be sown and fertilized every year, they concluded that the higher number of mechanical operations and larger amounts of fertilizer in the crop stage, leaving aside the larger amounts of chemical additives in the pulp production stage, were good reasons for sticking to eucalyptus paper. In any case, there is an increasing interest in the use of nonwood fibers for specialty paper production and their environmental impact assessment.34 Authors like Gonzales-Garcia (2010)7 and Van der Werf (2004)35 carried out LCA of hemp cultivation, as well as of other crops, in European countries such as Spain and France with similar climatic conditions to Italy, but the results obtained were quite different. In the first case,7 the carbon footprint calculated with the global warming potential 100 (GWP100),36 had a value of 1600 kg CO2 eq/ton of hemp fiber ready to be processed in a pulp mill, then considering cultivation, production and supply; in the second case,35 the same indicator resulted in a value of 2330 kg CO2 eq/ha (the functional unit adopted was 1 ha field production of hemp, including into the system boundaries only the processes up to the harvest and the transport to the farm. The yield of 1 ha of land, in the study cited, was 6720 kg of dry matter, so in this case the GWP100 is 0.34 kg CO2eq/kg dry matter). These values, beyond any discrepancy due to different methodological approaches, put in evidence a role of climatic and soil condition, specific of the site where the cultivation takes place (fertilizers needs, water, etc). Also the Ministere de l′Agriculture et de la Peche (France) performed a LCA of hemp cultivation and they considered the amount of stored CO2: they found out that, depending on the allocation method, the amount of CO2eq was in the range −1/ −2.9 kg CO2eq/kghemp.37 Due to the worldwide interest in energy crops, lately, Buratti and Fantozzi (2010)38 developed a new methodology to define the LCA of biomass production. They formulate new indicators, which are considered more suitable to evaluate biomass sustainability. Others authors compared the environmental implications of the production of ethanol from five lignocellulosic materials.39 This shows the increasing interest, not only from an analytic perspective, but also in the methodological point of view, for natural materials. The aim of the present work was to perform a life cycle assessment (LCA), according to ISO 14040-44,40,41 of hemp production (technical fiber and woody core) and its use as thermal insulator, so the production impacts of a hemp mat were assessed. Accordingly, the life cycle analysis of one ha land cultivated with hemp in Italy was carried out, and results compared with those previously obtained for Spain or France.7,35 The study was completed with the sustainability analysis of two walls, where the insulating performances were guaranteed alternatively by hemp-based or rockwool insulating panels. The environmental burden of hemp production and of the two walls containing either a hemp-based or a rockwool insulating panel was assessed using three indicators: greenhouse gas protocol (GGP), cumulative energy demand and Ecoindicator99. As for the GWP, considering that CO2 uptake is one of the major environmental benefits when dealing with vegetal-based materials, CO2 biogenic was accounted for. Indeed, like all other biobased products, such as wood, hemp has the capability of storing CO2 (biogenic CO2) during photosynthesis;32 however, consistently with the aims of their

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MATERIALS AND METHODS Goal and Scope. The purpose of this LCA study was to assess the sustainability of a hemp-based thermal insulator. In order to perform a detailed LCA, the quantification of different environmental impacts about the cultivation of one hectare of land by hemp was necessary. The environmental loads were associated to the two different coproducts: technical fiber and woody core. The sustainability of hemp fiber for building applications was investigated by considering an insulation mat made by hemp fiber (85%) and polyester fiber (15%). The functional unit was 1 m2 of hemp mat to be inserted in a wall having a thermal transmittance (U) equal to 0.2 W/m2-K. In the manuscript information about hemp cultivation (1 ha) are reported in order to give better comparability with literature studies dealing only with hemp cultivation, since no studies on the specific variety of hemp cultivated in Italy are available in literature. In addition the new ISO 15804 44“Sustainability of construction worksEnvironmental product declarations Core rules for the product category of construction” defines a declared unit as follows: “The declared unit is used instead of the f unctional unit when the precise function of the product or scenarios at the building level is not stated or is unknown.” Due to the different possible application of woody core and fiber in the construction field, according to ISO 15084, data for 1 kg of product are also reported in the manuscript. LCA followed a “from cradle to gate” approach. All the operations involved in the cultivation of the plant were considered: from plowing to sowing, then cutting, harvesting, and final processing that brought to production of technical fiber and woody core. Furthermore the production of the hemp based mat was considered. Throughout the study it was necessary to make various assumptions and hypotheses, explained later for each case. System Boundaries (Scenarios). The impacts were estimated from the acquisition of raw materials to production of woody core, fiber and dust, up to the production of a hemp7414



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Figure 1. Flowchart of the production of a hemp-based insulation panel.

This value refers to monoecius varieties (Carmagnola) cultivated in Italy. In this paper, an average production of 15 tons was considered. Secondary data taken from Ecoinvent database (www. ecoinvent.ch), one of the world’s leading supplier of consistent and transparent life cycle inventory (LCI) data, were: machinery production and maintenance, fertilizers production, electric energy, crops, irrigation, and fossil fuels. Allocation Procedures. Allocation was needed because the cultivation of hemp delivers three coproducts: (i) fiber, (ii) woody core, and (iii) dust. Typically, 1 ton of dried hemp yields a percentage equal to 75% of woody core, 20% technical fiber and 5% dust. The ISO 14040 suggests to respect physical relationships when possible, or use economic allocation when physical relationships cannot be applied to the system. Due to the very different market prices of the three coproducts, in this work both mass and economic allocation were used: physical quantities, such as biogenic CO2 and feedstock energy were always mass allocated, to comply with mass and energy balances. Mass Allocation. The mass outputs of the cultivation of 1 ha were 11.25 tons of woody core, 3 tons of fiber, and 0.75 tons of dust. Then, the allocation factors, when mass allocation was used, were the following:

based insulating panel. Fiber was used to make an insulator jacket to be employed in a wall having a thermal transmittance (U) of 0.20 W/m2.K. The end of life was not included, because of the numerous possible scenarios, and the final disposal of the product mainly depend on the intended end use and the possible mix with other materials like plaster and lime. System boundaries included all the emissions directly or indirectly generated. The production of a hemp-based panel was modeled according to the flowchart shown in Figure 1. Hemp cultivation was divided into different unit operations, which interact between them and the external surroundings by inputs and outputs of energy and materials. The flowchart identifies the process units that represent the steps involved in the system investigated: (1) Ploughing (2) Harrowing (3) Presowing fertilization (4) Sowing (5) Germination (6) Cutting and threshing (7) Windrowing (8) Baling and bales loading (9) Transport to scutching site (10) Scutching (11) Transport to panel production site; (12) Fiber preparation and mixing with polyester; (13) Panel production Every unit process received its input from the upstream unit, whereas its output represented the input for the downstream processes, according to the actual cultivation process. In this way the behavior of every single process unit was independent and was linked both to the operations that preceded it and the following, allowing the detection of all flows that refer to the single unit. Data Quality. Primary data were available for inputs and outputs directly linked to hemp cultivation, such as tractor consumption and use per ha, fertilizers, seeds, amount of water needed for irrigation, transport. The source of these data was the official Italian association of hemp cultivation (Assocanapa, www.assocanapa.org). The typical annual yield of the hemp variety considered in this study was in the range 13−16 ton/ha.

λw =

11.25 = 0.75 15

λf =

3 = 0.20 15

λd =

0.75 = 0.05 15

where λw, λf, λd, were the allocation factors for woody core, fiber and dust, respectively. Economic Allocation. The prices of the coproducts have a great variability, depending on many factors. The average prices, based on Italian data considered for economic allocation were equal to 0.25 €/kg for the woody core and 0.60 €/kg for the fiber. No economic value was attributed to dust. 7415



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In the germination unit process, a water volume of 120 m3/ ha for irrigation to develop a good root system and allow the development of the plant was necessary. This value is referred for irrigation in the Po Valley area and for normal condition of rainfalls (about 400−500 mm of rain during growing season from April to September). The use of a pump, power of 30 m3/ h, 22 kW for 4 h duration was considered. The scutching unit process needed 313 kg of fuel, necessary for working machinery. The transport of baled hemp to the first processing plant was assumed to be nearby the growing area and it was modeled using a EURO 4, 7.5- 16 truck, according to one hectar yield (15 t). The transport from the first processing plant to the hemp panel production site was assumed equal to 50 km using a EURO 4, 7.5- 16 truck. Unlike previous works,39,8 biogenic CO2 was considered in hemp cultivation. Usually, 1 g of dry biomass contains 0.5 g of C, so it was estimated that 1 ton of dry hemp contained 1.83 ton of biogenic CO232 Feedstock energy of dry hemp was estimated by considering the one of a similar fiber, such as kenaf LHV, from Ecoinvent database. Hemp Panel and CV.01 and CV.02 Walls. The insulation panel consisted of hemp (85%) and polyester fiber (15%), and it was treated with boron salts to improve the fire performance and the refractoriness to mold and insects. Figure 2 shows the stratigraphy of the wall (CV.01) where the hemp based insulation panel was inserted. A second wall

So when economic allocation was applied, only two products were considered. The allocation factors for 1 kg of either fiber or woody core were, respectively

€w =

0.25 = 0.29 0.85

€f =

0.60 = 0.71 0.85

Then, the allocation factors, referred to 15 ton of hemp cultivated, were λw =

€ wm w = 0.61 € wm w + €f mf

λf =

€f mf = 0.39 € wm w + €f mf

Where mw and mf are the mass of woody core and fiber obtained from 15 tons of hemp. LCIInventory Assessment. For each unit process of hemp cultivation, the use of New Holland machinery (T5000 tractor series) was considered. It was assumed that the same agricultural machine was used, that set different agricultural implements due to the process required. Then, fuel consumptions were calculated according to the different types of equipment attached, which varies power needs. Fuel consumption and power needs of the agricultural machine for the different unit process of cultivation are shown in Table 1. Table 1. Fuel Consumptions during the Different Operating Phases process unit ploughing harrowing presowing fertilization sowing cutting + threshing windrowing baling

fuel

tractor use

kg/h 14.63 14.63 8.78

h/ha 5 2.5 1.6

8.78 48.25 4.88 10.56

2 4 4 3

tractor consumption l

tractor consumption kg

87.57 43.79 16.81

73.13 36.56 14.04

21.02 232 23.35 37.95

17.55 193 19.50 31.69

Figure 2. Stratigraphy of wall made with hemp mat: 1. Plasterboard, 2. Insulation panel (hemp-based or rockwool), 3. Oriented strandboard, 4. Reinforced Concrete panel, 5. Cement plaster.

Inventory data related to the production of fertilizers used in the system (ammonium nitrate and potassium chloride) were taken from the Ecoinvent database, and they are reported in Table 2. Emissions of N2O, NH3, and NO from nitrogen fertilizers were considered, according to literature data.45,46 In the baling unit process the amount of wrap film necessary was considered in the Ecoinvent unit process used. In this phase, the inventory also considers aggregated data for all the plastic materials production processes and energy necessary for film production process.

(CV.02), where the insulation performance was guaranteed by a rockwool mat, was considered in order to compare the sustainability of a natural-based panel with respect to a mineralbased one. CV.01 and CV.02 are generic walls with the same technical elements that differ only by the insulating panel inserted. Data for the hemp-based thermal insulator were taken by considering mass allocation for hemp fiber and woody core and Ecoinvent database for polyester fiber. For the hemp panel production no literature data nor database information were available. So primary data from a similar production were obtained from an Italian industry that produces kenaf fiber panels mixed with 15 wt % of polyester. These data included the following phases: fiber preparation, carding, thermal binding, cutting of the panel, and packaging. For the production of the panel, the preparation and mixing of fibers needed

Table 2. Amounts of Seeds and Fertilizers Needed for the Cultivation of 1 ha Field input

amount [kg]

ammonium nitrate phosphate, as P2O5 potassium chloride, as K2O seeds

300 200 50 7416



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RESULTS AND DISCUSSION Hemp Cultivation. Results for hemp cultivation were calculated using the three methods above-described. Greenhouse Gas Protocol (GGP). Impacts of hemp cultivation on climate change are reported in Table 5 and 6,

0.0022 kWh/kgfiber and 0.001 l H2O/kgfiber. The actual panel production needed 0.16 kWh/kgpanel (electric energy) and 2.043 MJ/kgpanel (natural gas) and 0.0012 g of PE film/kgpanel for packaging. The panel here considered weighted 6.0 kg (density 30 kg/m3). Data for the rockwool insulation panel (both for fibers and mat production) were completely extracted from Ecoinvent database, except for the energy country mix that was changed to Italian mix, in order to be consistent with all the other input data. The characteristics of the two walls are reported in Table 3. The layer n.2 can be either hemp-based

Table 5. Emissions of CO2eq of 1 ha Cultivated by Hemp (Mass Allocation) product

Table 3. Technical Characteristics of CV.01 Wall: λ is Defined As Thermal Conductivity; RCd is the Conductivity Resistance and Rsi and Rse are the Internal and External Surface Resistancea N. inside 1 2-CV01 2-CV02 3 4 5 outside

name and description of the layer

thickness [m]

λ [W/ m_K]

RCd [m2K/ W]

hemp woody core fiber dust

Rsi, Rse[m2K/ W]

0.025 0.200

0.21 0.044

0.120 4.500

0.160

0.035

4.570

0.015

0.13

0.120

0.015

0.32

0.050

0.010

1.40

0.004

product hemp woody core fiber dust 0.04

The stratigraphy of CV.02 is equal to the one of CV.01, shown in Figure 2.

(CV.01) or rockwool (CV.02). The calculation of the thermal transmittance U is reported in the Supporting Information.Glue laminated timber and chipboard screws were also considered and their amounts are reported in Table 4. Table 4. Amounts of Accessories Technical Elements

glued laminated timber 20 × 10 chipboard screws inox 3.5 × 35/45

ρ [kg/ m3]

[n°/ m2]

450 8000

33.3

[m3/ m2 ] 0.033

uptake [ton CO2 eq/ha]

fossil [ton CO2 eq/ha]

total per kg [kg CO2 eq/kg product]

15 11.25

−26.01 −19.51

−27.6 −20.69

1.57 1.17

−1.73 −1.73

3.0 0.75

−5.20 −1.30

−5.52 −1.38

0.31 0.08

−1.73 −1.73

yield

total per ha [ton CO2 eq/ha]

uptake [ton CO2 eq/ha]

fossil [ton CO2 eq/ha]

total per kg [kg CO2 eq/kg product]

15 11.25

−26.01 −19.72

−27.6 20.68

1.57 0.96

−1.73 −1.75

3.0 0.75

−4.92 −1.37

−5.54 −1.37

0.61 0.00

−1.64 −1.82

where results of the cultivation of 1 ha are split for the different coproducts (hemp fiber, woody core and dust) and calculated both for mass and economic allocation. Besides total CO2eq emissions, uptake and fossil contribution are described, because these are the main contribution to the total emissions. Biogenic and land transformation shares are quantitatively not significant in the present study. Data are reported also for 1 kg of product. Mass allocation, of course, holds identical values for the three coproducts, when results are referred to 1 kg of product (−1.73 kg CO2eq/kg product). When considering the yield per ha of the single coproducts, the impacts associated to the production of woody core are the most relevant ones, due to the higher amount of woody core produced with respect to the others (fiber and dust). The overall impact, also considering hemp dust, for the cultivation of 1 ha is equal to about −26.01 ton CO2 eq/ha, whereas the fossil CO2 contribution is equal to 1.57 ton/ha. Economic allocation showed different values among the three products. In this scenario, the amount of CO2 uptake was mass-allocated among the three products, because it is a strictly physical quantity; instead, the fossil CO2eq emissions were economic allocated. Accordingly, the total CO2eq emissions of 1 kg of product resulted lowest for dust: this product does not have economic importance, so it does not hold any fossil contribution. When considering the two main products, woody core and fiber, it can be observed that the most expensive one (fiber) is the most impacting one. The CO2eq uptake is the most important contribution and according to what observe for mass allocation the cultivation of 1 ha is equal to about −26.01 ton CO2eq/ha, while the fossil CO2 contribution is equal to 1.57 ton/ha. The CO2eq uptake reported in Table 5 and 6 refers to the whole process, even if the contribution of hemp uptake is largely predominant. Mass allocation was the one chosen also to assess the impact of the wall. The reason for choosing mass allocation is due to

a

accessories technical elements

yield

total per ha [ton CO2 eq/ha]

Table 6. Emissions of CO2eq of 1 ha Cultivated by Hemp (Economic Allocation)

0.125 plasterboard hemp insulation panel rockwool insulation panel oriented strandboard reinforced concrete-panel cement plaster

Article

[kg/m2] 15 0.115

LCIA Methodology. The impact assessment phase (LCIA) was carried out by the quantification of three different indicators: (1) Greenhouse gas protocol (GGP): it allows to quantify the amount of CO2eq, by subdividing the different contributions of CO2eq (fossil, biogenic, land transformation and uptake). (2) Cumulative energy demand (CED): it is an indicator able to quantify the energy needs of the system, including feedstock energy, and separate renewable sources from the nonrenewable ones. (3) Ecoindicator99 H: it is a methodology where 11 categories grouped in three macro-categories of damage assessment (mineral and fossil resources ecosystem quality, human health) are weighted to give a single score. Details on the methods used are reported in the Supporting Information. 7417



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the fluctuations of market prices of fiber and woody core, so the reliability of this scenario is higher. The impacts of the different process units per ha of cultivated land, so not considering biogenic CO2, are reported in Figure 3. The impacts include the use of machinery and their maintenance. The processes of scutching and transport are not considered in the diagram.

respect to synthetic or mineral materials, when considering GGP, but they stock a quite high amount of renewable energy. Ecoindicator 99 H. The peculiarity of Ecoindicator 99 H, with respect to GGP and CED, is that it considers 11 different impact categories, whose potential damage is normalized and weighted, and the output is expressed in Ecopoints. Results of Ecoindicator 99 H are reported in Figure 5 and the output of Ecoindicator is expressed in points/ha.

Figure 5. Results of Ecoindicator 99 H expressed in points/ha. Figure 3. kg of CO2eq associated to the different process units per ha of cultivated land. CO2 uptake is not considered.

The most impacting category is “fossil fuels”, after normalization and weighting (see Supporting Information), due to the consumption of diesel (see Table 1). The category “respiratory inorganics” is the second most impacting one, due to diesel, machinery production and maintainance, and fertilizers production. Wall Impacts. Two indicators were adopted to assess the sustainability of a wall with a hemp-based thermal insulator: GGP, due to its widespread use in many different sectors, and CED, since energetic issues are always of utmost importance when dealing with buildings. Impacts of the production of the hemp-based thermal insulator are reported in Table 7. Impacts were divided according to the flowchart of Figure 1:

The most impacting process is fertilization, mainly due to P2O5 production impacting for 384 kg CO2eq (in the graph also the emissions of N2O are considered and it accounts for 84.5 kg CO2 equiv). Secondary impacts come from ploughing, cutting and baling. Cumulative Energy Demand (CED). Results for the energy needs of the system considered are reported in Figure 4. The impacts calculated for 1 kg of the two coproducts in the two allocation scenarios are shown.

Table 7. Impacts Calculated With GGP and CED for the Production of a Hemp-Based Insulation Panel. Impacts Are Divided for the Production Stages Reported in Figure 1 GGP production transport + scutching transport to panel production site panel production hemp CO2 uptake hemp feedstock energy total

Figure 4. CED impacts calculated for 1 kg each of the two coproducts in the two allocation scenarios (mass and economic).

Outputs for mass allocation, as already mentioned in the previous paragraph, are the same for fiber and woody core. The amount of nonrenewable energy (mainly due to fuels and field operations) is very low if compared to the amount of renewable energy needs. The reason of the high value of renewable energy was due to the feedstock energy of hemp. Indeed, all vegetable fibers and wood stock have quite high lower heating values (LHV) and, when they are not used for energy production, this energy remains stocked and not available. So, it can be observed that vegetal-based materials have very high advantages, with

[kg CO2eq] 0.428 0.131 0.067 4.54 −8.82 -4.28

CEDnon renewable CEDrenewable [MJ] 12.11 6.93 1.09

[MJ] 0.48 0.028 0.014

102.1

1.11

0 122.23

91.84 93.47

1. Production (materials, fuels production and hemp cultivation) 2. Transport and scutching 3. Transport to panel production site 4. Panel production (including polyester production) The GGP of the hemp panel production is the most important impact due to the high contribution of polyester fiber (3.14 kg CO2eq). The processing of the hemp panel production, instead, impacts for 1.40 kg CO2eq. For the same 7418



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noting, however, that about half of the energy requirement of the hemp-based mat is the feedstock energy of a renewable source (the hemp fiber) and it is not an actual energy consumption due to the production process. So, the comparison of the nonrenewable energy source, that is directly linked to the real energy needs of the two mats, allows to observe a reduction of 67% for the hemp-based mat. This is mainly due to the different production processes of the input materials: indeed, hemp is a fast growing herb that does not need important energy inputs, while rockwool needs high energy inputs during its production process (i.e., melting, fiber forming and collecting, hardening and curing furnace, and furnace operation). From the above results, it can be assessed that, by taking into consideration both GGP and CED indicators, the choice of a natural-based thermal insulator is a more sustainable option compared to a mineral-based one. In summary, the present work aimed at introducing results from the analysis of the life cycle of the production of a hempbased panel. Starting from hemp cultivation, different allocation methodologies, mass and economic, were applied to the coproducts (woody core, dust and fiber) and different indicators (GGP, CED, Ecoindicator 99 H) were calculated. As expected, when considering GGP indicator, the main contribution to the final result was given by the high amount of CO2 uptake. When considering two walls, with equal thermal characteristics and different insulating panels (rockwool and hemp based), the two indicators considered (CED and GGP) showed that the use of a natural material such as hemp improves the sustainability performances of the final product.

reason the CEDnonrenewable is highest during panel production, due to production of polyester and its feedstock energy. Results of GGP for the two walls (CV.01 and CV.02) and the two thermal insulators considered, hemp in CV.01 and rockwool in CV.02, are reported in Figure 6. Data refer to 1

Figure 6. kg CO2eq calculated for 1 m2 of the two walls (CV.01 and CV.02) and for the respective amounts of the two thermal insulators considered, that is, hemp in CV.01 and rockwool in CV.02. Hempbased panel weights 6.0 kg, whereas rockwool mat was 6.4 kg.

m2 of wall and it is reported also the contribution of the specific amount of each thermal insulator. Results show that CV.01 wall is highly sustainable with respect to CV.02, due to the high content of hemp fiber, that allows for a negative value of CO2eq. Indeed, the direct comparison between hemp-based and rockwool insulator mat shows the much higher sustainability of hemp. The lower CO2 values of the two walls, compared to the two mats, are due to the presence in the walls of a layer of an oriented strandboard and glued laminated timber (Tables 3 and 4) that hold negative values due to the CO2 uptake by wood. CED shows a more balanced situation (Figure.7): as expected CV.01 shows a lower need of nonrenewable energy,

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ASSOCIATED CONTENT

S Supporting Information *

Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: +39 0223993234; fax: +39 0270638173; e-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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Figure 7. CED of 1 m2 of the two walls (CV.01 and CV.02) and the two thermal insulators considered, hemp in CV.01 and rockwool in CV.02.

while CV.02 holds lower values for what concerns renewable energy. The sum of the two contributions leads to a CED value of 215.5 and 302.2 MJeq for the hemp mat and the rockwool mat, respectively. So, the use of a hemp mat allows for a reduction of 28.8% of the global energy requirement. It is worth 7419



Article

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