- Email: [email protected]
Life cycle assessment of wood-fibre-reinforced polypropylene composites
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
journal homepage: www.elsevier.com/locate/jmatprotec
Life cycle assessment of wood-fibre-reinforced polypropylene composites Xun Xu a,∗ , Krishnan Jayaraman a , Caroline Morin b , Nicolas Pecqueux b a
Department of Mechanical Engineering, University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand b Institut Francais de Mecanique Avancee (IFMA), Campus de Clermont-Ferrand les C´ezeaux, BP 265, 63175 Aubiere Cedex, France
a r t i c l e
i n f o
a b s t r a c t
Article history:
Composites of polymers reinforced with natural fibres have received increasing attention.
Received 13 February 2007
Natural fibres such as sisal, flax, jute and wood-fibres possess good reinforcing capabil-
Received in revised form
ity when properly compounded with polymers. These natural fibre-reinforced composites
22 June 2007
find a wide array of applications in the building and construction industry and the auto-
Accepted 27 June 2007
mobile industry. The use of natural fibres in composite materials does not automatically make it a “sustainable material”, i.e. “natural” may not necessarily equal “environment friendly”. The literature in the field of natural fibre-reinforced composites with respect to
Keywords:
their environmental standing is reviewed in this paper. A life cycle assessment has been
Wood-fibre
carried out for wood-fibre-reinforced polypropylene composite preforms produced by com-
Polypropylene
pression moulding in comparison with those of polypropylene. Three levels of fibre contents,
Composite
10%, 30% and 50% by mass, have been used. The level of environmental impact caused by
Life cycle assessment
transportation is also studied. This study introduces a new term called “material service
Natural fibre composite
density”, which is defined as the volume of material satisfying a specific strength requirement (tensile strength in this study). The rationale behind this is that specific volumes of different materials are required to withstand a given mechanical load (tensile load in this case). Comparison of the material service density for two materials: wood-fibre-reinforced composite and polypropylene are conducted. The results showed that when material service density is used as the functional unit, wood-fibre-reinforced composite demonstrated superior environmental friendliness compared to polypropylene. © 2007 Elsevier B.V. All rights reserved.
1.
Introduction
Over the last decade, composites of polymers reinforced by natural fibres have received increased attention. Natural fibres such as sisal, flax, jute and wood-fibres possess good reinforcing capability when properly compounded with polymers. The advantages of bio-fibres over synthetic fibres such as glass fibres are low cost, low density, renewability, favourable
∗
Corresponding author. Tel.: +64 9 373 7599; fax: +64 9 373 7479. E-mail address: [email protected] (X. Xu). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.06.087
values of specific strength and specific modulus, excellent chemical resistance and significant processing benefits which require minor changes to equipment. Thermoplastic polymers, such as high-density polyethylene and polypropylene, possess shorter manufacturing cycle times and reprocessability despite problems with high viscosities and poor fibre wetting. The renewability of natural fibres and the recyclablity of thermoplastic polymers provide an attractive eco-friendly
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
169
Fig. 1 – Natural fibres used for reinforcement.
quality to the resulting natural fibre-reinforced thermoplastic composite materials. Natural fibres can be classified into six types as shown in Fig. 1 (Bos, 2004). Natural fibre-reinforced thermoset and thermoplastic composites have found a wide array of applications in the building and construction industry in products such as door and window frames, decking material, railings for parapet walls and furniture sections, and the automobile industry in items such as door panels, seat backs, headliners, package trays, dashboards and trunk liners. Economics and other related factors in many developing countries, where natural fibres are abundant, demand scientists and engineers to apply appropriate technology to utilise these natural fibres as effectively and economically as possible to produce good quality fibre-reinforced polymer composites for housing and other needs (Segetin et al., 2007). The use of natural fibres in composite materials does not automatically make it a “sustainable material”, i.e. “natural” may not necessarily equal “environment friendly”. A better evaluation of the fundamental loops and processes of the entire life cycle of a material, such as the stages of extraction, use and disposal is necessary to make a judgment about the environmental characteristics of the material. Life cycle assessment (LCA) is a tool specifically developed for assessing the overall environmental burden of a product. The results can be used to optimize the environmental performance of a single product (eco-design) or to optimize the environmental performance of a company. Common categories of assessed damages in LCA are global warming (greenhouse gases), acidification, summersmog, ozone layer depletion, eutrophication, ecotoxic and anthropotoxic pollutants. The LCA method entails four parts (ISO14040, 1997; ISO14041, 1998; ISO14042, 2000): • Goal definition defines the aim and the scope of the study as well as the function and the functional unit of the studied product. • Life cycle inventory lists pollutant emissions and consumption of resources per functional unit. • Life cycle impact assessment classifies and evaluates the environmental impact of the pollutants emitted during the life cycle. • Life cycle interpretation allows one to interpret the results and to estimate the uncertainties. In the case of sustainable biomass, it is possible that far more material may have been extracted and translocated than
what is actually used in making the end product. An optimal material technology has, therefore, to consider resource consumption and the amount and the quality of waste material during the entire life cycle. These days however, the choice of material is still largely motivated by economic and mechanical criteria. The remaining text first reviews some of the literature concerning LCA performed on natural fibre-reinforced composites. The main body of the paper describes the LCA performed on a natural fibre- (i.e. wood-fibre) reinforced polypropylene composite in the context of the local (New Zealand) situation.
2.
Literature review
LCA allows us to understand the real environmental impact of a product, especially in the location where it is produced. Jolliet et al. (1994) pointed out when concluding their study on biomaterials, that “environment friendly” is different from “natural”. “Material service density”, defined as mass of material satisfying service requirements, is in fact a key factor for both technological and environmental optimization, especially in the case of long distance transport. LCA has long been associated with different material processing technologies and their end results. Ong et al. developed a semi-quantitative pre-LCA tool for assessing the environmental impacts of the production of a printer (Ong et al., 1999, 2001). Most of the research work seems to have focused on development of an effective means of assessing the environmental impact for different types of cutting fluids (Sokovic and Mijanovic, 2001; Alves and de Oliveira, 2006; Tan et al., 2002). Some effort has been spared on LCA for manufacturing processes such as cold rolling production (English et al., 2006) and welding processes (Yeo and Neo, 1998). There is limited research reported on LCA for composite materials and their products. De Vegt and Haije (1997) compared three reinforced composite rotor blades of a wind energy converter, flax fibre-reinforced epoxy, carbon fibre-reinforced epoxy and glass fibre-reinforced polyester. The LCA results gave a better score to flax fibre-reinforced composite (1.85 points1 ) against 2.4 points for the other two materials. They used a simplified LCA method called “matrix method”. It used
1 The Eco-indicator 99 single value expressing impact in three safeguard areas: damage to human health and the ecosystem and depletion of resources.
170
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Table 1 – Example for the “matrix method” (De Vegt and Haije, 1997) LCA phase
Considerations
Rotor-blade Flax fibre
Carbon fibre
Glass fibre
0
–
–
Production
Energy requirement
Use
Longevity, energy consumption, maintenance
0
0
0
Disposal
Landfill, combustion, recycling
0
0
0
0
1
1
Total
a table with the materials studied in columns and the different phases in rows (Table 1). Zero, pluses and minuses are entered in the cell and the totals are summed at the bottom. Though rough and more subjective, it can help to decide if a new material clearly outweighs the current one. Hansen et al. conducted a comparative LCA for two interior side panels of an Audi A3 (flax–jute reinforced epoxy and acryl-nitrile butadiene styrene copolymer also known as ABS) (Hansen et al., 2000). Major energy consumption happens during the use phase, i.e. fuel consumption which represents 80% of the total energy for manufacture, use and disposal of a car. As a result, the natural fibre composite side panel, as compared to the polymer panel, is ecologically preferable considering material, energy flows and emissions. Apparently, the utility phase of a car reveals substantial ecological advantages due to the weight difference. ` Corbiere-Nicollier et al. carried out LCAs for transport pallets made from glass fibre-reinforced PP, and China reed (CR) ` fibre-reinforced PP (Corbiere-Nicollier et al., 2001). The CR pallet consumes significantly less primary non-renewable energy. The strong primary non-renewable energy reduction for CR is attributed to three factors: (a) substitution of energy intensive glass fibre production by the low energy natural fibre production; (b) indirect reduction in the use of polypropylene linked to the higher proportion of China reed fibres used; (c) reduced pallet weight, which reduces fuel consumption during transport. The same study reports a net bonus for the incineration of PP of 21.5 MJ/kg and of 8.3 MJ/kg for natural fibre (China reed in this case). Glass fibres cost energy, 1.7 MJ/kg, during incineration and add negatively to the total Eco-indicator. For the natural fibre-reinforced composite part this means that about 25% of the energy costs of the production of the part are won back by incineration. For the glass reinforced part, which costs almost twice as much energy to produce in the first place, around 13% of the energy costs are won back by incineration. It was concluded that an environmental advantage of about 30% can be had due to the use of the natural fibre-reinforced material and a significant reduction of energy consumption due to weight saving during the use phase. Finally, use of China reed fibre as reinforcement in plastics proves advantageous from an ecological point of view, only if the CR pallet has a minimum lifetime of 3 years. Schmidt and Beyer conducted simplified LCAs for two designs of an insulation component in a Ford car (Schmidt
et al., 1998). One component is made of polymer reinforced by glass fibres, and the other is reinforced by hemp fibres (30% weight). The results of this study were only presented in the form of benefit values between natural fibre and glass fibre component. Thus, the natural fibre component requires 88.9 MJ less of the total energy demand. Looking at the emissions, the natural fibre component is also economic in that 8.18 kg of CO2 emissions, 0.0564 kg of SO2 emissions, 0.002 kg of phosphate emissions and 0.018 kg of nitrate emissions can be avoided. LCA based on the three phases as in the above-discussed cases, is obviously the closest to reality. Due to weight advantage, it seems to be a common phenomenon with natural fibre-reinforced composites that the longer a product life is, the more significant the environmental benefits. In a study on flax fibre-reinforced composites (Bos, 2004), an advantage is seen during the production phase, but benefits are more than obvious during the use phase because of its weight saving. This echoes the discussion on longevity of a product. In this research, the composites are made from matrices (epoxy resin, unsaturated polyester resin and polypropylene) and combined with either flax or glass fibres in different amounts (20%, 40% and 60%). The analysis also concluded that the mechanical properties are determined by the fibre, whereas the environmental impact is mainly related to the matrix. Cinar analysed the environmental impact of wood panels manufactured in Turkey (Cinar, 2005). LCA was applied to different kinds of wood-based panels, surface and edge treatments, and their respective manufacturing processes. According to the results, standard particleboard had an environmental impact lower than standard fibreboard (72%
Fig. 2 – Composite preform production.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
171
Fig. 3 – Process of creating a composite preform.
improvement). For surface and edge finishes, a low-density laminate is preferred to a high-density laminate (36% improvement). Wotzel et al. studied only the component manufacturing stage of an Audi A3 panel made from a hemp fibre epoxy composite (Wotzel et al., 1997). It was found that the natural fibre component uses 45% less energy than its alternative made of ABS co-polymer. However, water emissions of nitrates and phosphates, and nitrogen oxide (NOx) emissions to air are higher as a result of fertilizer applications in hemp cultivation. Overall Eco-indicator point scores are about 8% less for the hemp-fibre epoxy composite. Not surprisingly, the researchers found the weight saving for natural fibre-reinforced panels adds further benefits. In a study comparing hemp fibre mat thermoplastic with glass fibre composite (polypropylene is used as matrix), a significant energy savings of 60% per tonne of product by using natural fibre reinforcements can be expected through the following means (Pervaiz and Sain, 2002): (a) reducing use of PP by using higher proportion of natural fibres; (b) actual substitution of high-energy consuming glass fibres; (c) low weight of natural fibre composites; (d) saving in land filling efforts. Moreover, replacing even 20–25% glass fibre plastics with natural fibre composites can make a lot of difference for industrialized states, to curtail not only greenhouse gas emission but also to claim ‘carbon credit’ for these fibres.
Fig. 4 – Energy consumption of the vacuum oven.
Johansson studied a number of materials, including woodfibre-reinforced composite (Johansson, 2005). The suggested biocomposites, mixing PLA (polylactic acid) with pulps from wood-fibre, show promising environmental performance. This is mainly attributed to the use of wood pulp. The biocomposites shows a lower environmental impact than PLA and PET (polyethylene terphthalate) on most categories in both the CML (Centre of Environmental Science Leiden – Centruum voor Milieukunde Leiden) (Heijungs et al., 1992) and Ecoindicator methods. It combines the physical properties of a plastic material and the relatively low environmental impact of the pulp. In summary, the environmental standing for natural fibre composites as compared to their counterparts, e.g. synthetic fibre composites and polymers is not as conclusive if only the production phase is considered. The situation improves with sufficient evidence when use phase is included in LCA. When this is the case, the longevity of the product introduces a “magnification” factor. Similar to the use phase, the disposal phase also improves the environmental standing by giving back some energy and saving landfill space for example. Based on these findings, it seems that LCA for the production phase may hold the key to the final environmental standing of natural fibre composites. Any results that are at least not inferior to the compared materials will almost give it a favourable score in environmental terms. The following study aims to ascertain the environmental standing of wood-fibre-reinforced polypropylene composites by conducting an LCA for the production phase only.
Fig. 5 – Energy consumption of the hydraulic heated press.
172
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
from the accompanying Australian LCA database (SimaPro, 2006).
3.2.
Fig. 6 – Electricity generation by resource in New Zealand in 2004 (PJ).
3. LCA of wood-fibre-reinforced polypropylene composite 3.1.
Materials
Composite preforms are made of polypropylene and woodfibres. Polypropylene is originally in the form of granulated powder. The length of the fibres varies from 1 to 4 mm, and applied when composite sheets are made, with no particular orientation or patterns. The composite preform can have three or five layers (Jolly and Jayaraman, 2006), depending on the thickness of the preform. In this study, 2-mm sheets are considered, therefore a three-layered structure is adopted, i.e. one layer of fibre sandwiched between two sheets of PP (Fig. 2). The sheet has the size of 127 mm × 127 mm (5 in. × 5 in.). Fig. 3 shows the process of creating wood-fibre-reinforced composite preforms. The figure also defines the boundary of the LCA in this study.
Scope and goal
Natural fibre composite preforms are the common “intermediate stage” materials from which different products can be made. This study analyses wood-fibre composite preforms. While this gives a well-defined scope for LCA from the product fabrication point of view, two other factors also provide justification: (1) the situation improves with sufficient evidence when use phase is included, and (2) its recycling (minus disassembly) processes tend to be less variational. This study introduces a new term called “material service density”, which is defined as the volume of material satisfying a specific strength requirement (tensile strength in this study). The rationale behind this is that specific volumes of different materials are required to withstand a given mechanical load (tensile load in this case). Two sets of LCA are conducted: • Comparison of composites with three levels of fibre contents: 10%, 30% and 50% (with and without transportation included). • Comparison of the material service density for two materials: wood-fibre-reinforced composite and polypropylene. Polypropylene is sourced from Australia by sea and woodfibre from Rotorua, New Zealand. The preform sheets are made in a factory in Auckland. SimaPro software system has been used for LCA; the inventory data are primarily extracted
3.3.
Inventory
3.3.1.
Sources and production of wood-fibre
Wood-fibres usually come from two different sources: roundwood (debarked wood, logging residues and thinning) and industrial wood residues (sawdust, shavings, offcuts and slabs). This study considers debarked wood as the source of the wood-fibre. The debarked logs are chipped into pieces of 20 mm × 20 mm × 8 mm dimension using hammer mills or drum chippers in its “primary breakdown;” the energy used for the “primary breakdown” is known to be 2000–3000 kWh/t. Moreover, for the chipping process, 2 kg of water per tonne of wood is used. Chipping is followed by the “secondary breakdown,” also called the “refining” process, which extracts the fibres from the chips. Thermo-mechanical pulping has been widely used; it involves pre-steaming of chips for a short period before they are refined in a pressurised container. Mechanical pulping processes consume a large amount of electrical energy and water. However, they also yield a good amount of fibre, e.g. 80–90% recovery of total fibre. Mechanical pulping processes are cheaper to operate than more sophisticated chemical-based systems. There are also fewer environmental issues such as chemical contamination of sites and unpleasant smells. The secondary breakdown is achieved through a pressurised disc refiner; the energy consumption for this secondary breakdown
Fig. 7 – New Zealand net electricity generation and CO2 emissions in 2004.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Fig. 8 – New Zealand net electricity generation in 2004.
is estimated to be 250–400 kWh/t of bone-dry softwood fibres and somewhat less for hardwood fibres.
3.3.2.
Sources and production of polypropylene (PP)
PP produced in Australia is considered in this study; this takes into account three different PP plants, Kemcor, Montell-Clyde and Montell-Geelong, each having a market share in Australia of 19%, 44% and 37%, respectively. Since the PP considered is produced in Australia, shipping is also considered according to the functional unit. A distance of 1200 km is used as the average distance from the three plants to Sydney; the road trip by truck is assumed to be of 50% efficiency (one trip full, the return empty). The sea distance from Sydney to Auckland is taken to be 2150 km. The same 50% efficiency is assumed for land transport from Ports of Auckland to the factory where the preforms are made over a distance of 50 km. The database does not include the characteristics of transportation in NZ, so it is assumed that a 30 t truck has the same impact in NZ as in Australia. PP in granular form is considered to improve the adhesion with the fibres. This means that additional energy is consumed in conversion to the sheet form.
173
Fig. 9 – New Zealand CO2 emissions from combustion fuel type in 2004.
volume of fibres placed inside the chamber and (3) the heat loss. Maximum energy usage can be assured if the chamber is filled up with fibres. Therefore, the following assumptions are made: Working temperature: 90 ◦ C. Maximum power (600 W) to pre-heat the chamber (25 min). Power down to 20% of maximum power over next 25 min. Use the thermal inertia to reach 90 ◦ C at around 75 min mark. • Fibres are placed in the oven at the 75 min mark. • Use 20% of maximum power to maintain the temperature for the entire duration of the process.
• • • •
The energy consumption of the oven to dry the fibres corresponds to the area under the curve as shown in Fig. 4. Considering 6 h drying after the stabilization of temperature and one batch per day, the total energy that the oven uses is 25 × 600 + 25 × ((600 − 120)/2) + 25 × 120 × 2 + 6 × 120 60 = 1.17 kWh
3.3.3.
Fabrication of composite performs
During normal storage, the moisture content of the woodfibres increases; this leads to poor mechanical characteristics when used to make preforms. Therefore, fibre drying is always the first step. For this study, a common vacuum oven with an inside chamber of 19,664 cm3 (0.7 ft3 ) is used. Considering the common use, fibres need to be in the oven for 6 h at 90 ◦ C and a pressure of 0.8355 bar (25 in./Hg). Three factors are to be considered: (1) the energy needed to pre-heat the whole chamber to a certain temperature, (2) the
A manual hydraulic heated press (Carver press no. 4386 Model CH – electrical consumption: 1400 W, 230 V ac, 7 A) is used to produce the preforms. The energy spent by the operator to apply the pressure on the platens is not considered in this study. For information, this pressure is around 6.25 bar. Like the vacuum oven, efficiency coefficient, thermal loss, etc. are difficult to obtain, so the same method is used to calculate the amount of energy used. The two moulds are heated from a room temperature of 20 ◦ C. This phase takes 30 min
Fig. 10 – Average electricity in New Zealand.
174
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Fig. 11 – SimaPro model for composite perform production.
and the Carver system uses thermal inertia in the last 5 min to reach the required working temperature, 200 ◦ C. The two Teflon sheets, the fibre mat and the two PP sheets are put into the moulds at the 35 min mark. The sheet is pressed down for nearly 5 min before it is taken out to set. It is assumed that 90 sheets are produced at each power-up of the press. The process operation regime is shown in Fig. 5. The total energy consumption for making 90 sheets of the composites can be calculated as follows: 1400 × 25 +
(1400 − 280) × 5 + 280 × 5 × 2 + 280 × 5 × 90 2
New Zealand energy profile. As shown in Fig. 6, New Zealand electricity comes from different sources. Fig. 7 (Dang and Cowie, 2006) shows the electricity generated through different sources and the CO2 emissions for each. It is clear that hydro and fuels represent two contrasting resources or power generation in New Zealand. Figs. 8 and 9 show the total electricity generation breakdown, in terms of percentages, of each natural source, and total CO2 emissions from the combustion type of energy sources (Dang and Cowie, 2006). Based on the values in Figs. 6 and 7, an “average electricity/NZ” entry can be created in SimaPro (2006) (Fig. 10).
= 166, 600 Wmin = 2.78 kWh = 10 MJ
3.3.4.
Energy profile
As the Australian database does not contain NZ energy profile, the New Zealand Energy in Brief for year 2004 published by the New Zealand Ministry of Economic Development in March 2006 (Dang and Cowie, 2006) has been used to create the
Fig. 12 – Comparison of the composite (30% fibre) and the PP sheet on different categories.
3.4.
Assessment
3.4.1.
Characterisation
In SimaPro, the substances that contribute to an impact category are multiplied with a characterisation factor that expresses the relative contribution of the substance towards
Fig. 13 – Weighting effect on the composite and PP sheets.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
the impact category. Therefore, the characterisation factor can be seen as an equivalence factor. For example, the characterisation factor for CO2 in the impact category, climate change, can be equal to 1, while the characterisation factor of methane can be 21. This means release of 1 kg methane causes the same amount of climate change as 21 kg of CO2 does. In other words, the climate change caused by methane is 21 times more sever than that by CO2 . It is also possible to define a specific characterisation factor for each subcompartment of a substance. This is only necessary when a particular subcompartment of a substance is of interest in an LCA.
3.4.2.
Normalization
Many methods allow the impact category indicator results to be compared by a reference or normal value. This means the impact category is divided by a reference. The reference may be chosen freely, but often the average yearly environmental load in a country or continent, divided by the number of inhabitants is used as the reference. After normalization the impact category indicators all get the same unit, e.g. 1 year, which makes it easier to compare them. Normalization may also be applied on characterisation and damage assessment results, depending on the structure chosen for a particular method.
3.4.3.
Weighting
Some methods allow weighting across impact categories. This means the impact or damage category indicator results are multiplied by the weighting factors, and are added to form a total score. Weighting can be applied on normalized or not normalized scores, such as environmental priority system (EPS) which does not have a normalization step. It is also possible to stop at the normalization step as in the Centre of Environmental Science Leiden method (CML 92).
3.4.4.
Assessment methods
Eco-indicator 99 is used as the assessment method. It assesses the environmental impact in the following 11 categories: • • • • • • • • • • •
carcinogens; respiratory organics; respiratory inorganics; climate change; radiation; ozone layer; ecotoxicity; acidification/eutrophication; land use; minerals; fossil fuels.
175
• EQ: ecosystem quality (unit: PDF × m2 yr; where PDF stands for potentially disappeared fraction of plant species; m2 stands for the area size and yr (year) stands for the time period to obtain the damage). • R: resources (unit: MJ surplus energy; additional energy requirement to compensate lower future ore grade). Eco-indicator 99 has a damage assessment step. The impact category indicator results that are calculated in the characterisation phase, are added to form damage categories. Addition without weighting is justified here because all impact categories that refer to the same damage type (like human health) have the same unit (for instance DALY). This procedure can also be interpreted as grouping. The damage categories (not the impact categories) are normalised on a European level (damage caused by one European per year), mostly based on year 1993 as the base year, with some updates for the most important emissions. Please note that the normalization set is dependent on the perspective chosen.
3.4.5.
Assessment results and discussions
Three sets of comparative assessments have been carried out using SimaPro involving three different levels of fibre contents: 10%, 30% and 50% by mass. The same is done for situations with and without transportation taken into account. To save space, only the results involving 30% of fibre content are graphed (Figs. 12–14). It is obvious that use of fibres in the composite leads to direct reduction in environmental impact. This is proportionate to the amount of fibre used. When transportation is considered, i.e. the transportation of fibres inside New Zealand and PP from Australia to New Zealand, an 8% increase in impact is witnessed. The above analysis is effectively based on the mass functional unit, i.e. the same mass is assumed when comparing the wood-fibre-reinforced PP composite and PP. In actual engineering applications, materials are used to serve certain strength requirements, e.g. tensile strength. Other times, the same volume is needed to serve a functional purpose. In both cases, the environmental benefit exhibited by the wood-fibre-reinforced PP composite will be further “magnified”.
Fig. 11 shows the SimaPro model for creating the composite preforms from polypropylene and wood-fibres. In the Eco-indicator 99 method, normalization and weighting are performed at damage category level (endpoint level in ISO terminology). There are three damage categories: • HH: human health (unit: DALY = disability adjusted life years; this means different disability caused by diseases are weighted).
Fig. 14 – Global comparison between the composite and the PP sheets.
176
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
3.4.6.
Use of volume functional unit
When a similar volume is required in making a particular product, the physical densities of both the composite and PP come into play. It is obvious that the wood-fibre-reinforced PP composite will have lower density than PP and it is dependent on the density of the (dried) wood-fibre. Assume f and P are the densities of wood-fibre and PP, respectively. The density of wood-fibre-reinforced PP composite (c ) with v percentage of fibre in volume, or m (m = 30% in this case) percentage of fibre in mass can be obtained as follows: c = f × v + P × (1 − v) = P + (f − P )v (kg/m3 )
=
mc = Ac × h × c
m/f (m/f ) + ((1 − m)/P )
and
mP = AP × h × P
The additional PP in mass PPm , in percentage terms, can be calculated as PPm =
(1)
The moisture level varies a great deal with wood-fibres. This is also true even with dried fibres. Determination of its accurate density value is therefore not an easy task. According to Bowis (Bowis, 1997), one can assume, f = 400 kg/m3 . Given the PP’s density P = 900 kg/m3 , the ratio of fibre in volume (v) can be calculated as Wood-fibre volume ratio : v =
density of the composite (c = 650 kg/m3 ) and that of PP (P = 900 kg/m3 ). Assuming h is the third dimension, e.g. height of the component, the required mass of the composite (mc ) and that of PP (mP ) can be expressed as
=
mP − mc AP × h × P − Ac × h × c %= % mc Ac × h × c AP × P − Ac × c % Ac × c
(5)
According to Eq. (4) PPm =
AP × P − (P /c )AP × c c × P − P × c %= % P × c (P /c )AP × c
(6)
The literature (van Houts et al., 1997) suggested that the tensile strength of wood-fibre-reinforced PP composite with 30% of fibre mass is around 30 MPa and that of PP, 23 MPa. The above formula can be expressed as
0.3/400 = 0.5 (0.3/400) + (0.7/900)
PPm =
c × P − P × c 30 × 900 − 23 × 650 % = 81% %= P × c 23 × 650
This means that for a composite of 30% fibre and 70% PP by mass, the volumes of fibre and PP are nearly the same. The density of the wood-fibre-reinforced PP composite with 30% of fibre mass can also be calculated as
This means that to withstand the same tensile load, 81% more of PP in mass is needed than if the composite is used.
c = P + (f − P )v = 900 + (400 − 900) × 0.5 = 650 (kg/m3 )
4.
3.4.7. “Material service density” for satisfying the strength requirement When both wood-fibre-reinforced PP composite and PP products are designed to suit a particular strength requirement, less wood-fibre-reinforced PP composite (in both volume and mass) is actually needed than PP. This is based on the fact that the former has lower density as well as superior tensile strength than those of the later. Assume c is the tensile strength for the composite material and P the tensile strength for PP, then c =
F Ac
(2)
P =
F AP
(3)
where F is the force applied and Ac and AP are the area of crosssection for the composite and PP component, respectively. Therefore, Ac =
P AP c
(4)
This means that to meet the same tensile strength requirement, one would need to use (1 − P / c )% more volume of PP than that of the composite if composite is used. When volume is translated into mass, such an increase is further “amplified” due to the difference between the
Conclusions
There has been little literature on life cycle assessment on natural fibre-reinforced composite although scientific research on this type of materials has been on a steady rise. This is perhaps attributed to the drive toward using environmentally friendly materials. However, the literature shows a non-conclusive environmental effect when only the production phase of such composites is studied. During the cultivation stage, the use of pesticides and other types of chemical products can give a negative impact on the environment. On the brighter side, the use and the disposal phase of such composites demonstrated a clear advantage from the environmental point of view. Natural fibre-reinforced composites are generally lighter, which helps save fuel during transportation. At the disposal phase, more energy can be claimed back through processes such as incineration. The life cycle assessment on the wood-fibrereinforced polypropylene composite, locally manufactured in New Zealand, with PP imported from Australia, revealed some results similar to those discussed above. Yet, some interesting discoveries were made. • Transportation of fibres and PP does not have a significant effect. • In the composite, the PP content is the dominant factor on environmental damages; use of wood-fibres in the composite (e.g. 30%) has rather a mild effect. • Environmental standing of the wood-fibre-reinforced polypropylene composite further improves in the following situations:
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
◦ When a similar volume is required in making a particular product, the environmental standing of the composite further improves. This is due to the fact that the composite has lower density than PP. For a composite of 30% fibre and 70% PP, the density value is 650 kg/m3 as compared to that of PP being 900 kg/m3 . ◦ When both wood-fibre-reinforced PP composite and PP products are designed to suit a particular tensile strength requirement, the environmental standing of the composite also improves. This is because less composite (in both volume and mass terms) is actually needed than is PP. This is based on the fact that the former has superior tensile strength as well as lower density. To withstand the same tensile load, the same composite (30% fibre and 70% PP) only needs less than a quarter of PP in mass if PP was used. The study is based on the preform sheets, which is an “intermediate material” for further making final products. Therefore, this LCA was for a partial, but a major portion of, production phase. In a way, the study confirmed a hypothesis that if the production stage of the wood-fibre-reinforced PP composite exhibits a better environmental standing than that of PP, one can safely assume that the entire life cycle of the wood-fibre-reinforced PP composite possesses a better environmental standing than that of PP.
references
Alves, S.M., de Oliveira, J.F.G., 2006. Development of new cutting fluid for grinding process adjusting mechanical performance and environmental impact. J. Mater. Process. Technol. 179 (1–3), 185–189. Bos, H., 2004. The Potential of Flax Fibres as Reinforcement for Composite Materials. Eindhoven University of Technology. Thesis available on http://www.tue.nl/bib. Bowis, M.E., 1997. Mechanical Properties and Formability of HTMP Wood-Fibre Composite-Polypropylene Composite Sheets. PhD Thesis. Department of Mechanical Engineering, University of Auckland, New Zealand. Cinar, H., 2005. Eco-design and furniture: environmental impacts of wood-based panels, surface and edge finishes. For. Prod. J. 55 (11), 27–33. ` Corbiere-Nicollier, T., Gfeller, L.B., Lundquist, L., Leterrier, Y., Manson, J-A.E., Jolliet, O., 2001. Life cycle assessment of biofibres replacing glass fibres as reinforcement in plastics—resources. Conserv. Recycl. 33, 267–287. Dang, H., Cowie, P., 2006. New Zealand Energy in Brief March 2006, ISSN 1177-2824 (http://www.med.govt.nz/energy/info/). De Vegt, O.M., Haije, W.G., 1997. Comparative Environmental Life Cycle Assessment of Composite Materials—ECN-I-97-050. English, M., Castellucci, M., Mynors, D.J., 2006. Eco-efficiency of the cold roll formed product supply chain. J. Mater. Process. Technol. 177 (1–3). Proceedings of the 11th International Conference on Metal Forming, July 3, 2006, pp. 626–629. Hansen, A., Flake, M., Heilmann, J., Fleißner, T., Fischhaber, G., 2000. Life Cycle Studies of Renewable Raw Materials – Natural
177
Fibre Reinforced Component and a Varnish – Bio-Resource Hemp 2000, Wolfsburg, September 13–16, 2000. ´ J., Huppes, G., Lankreijer, R.M., Udo de Haes, Heijungs, R., Guinee, H.A., Wegener, S.A., Ansems, A.M.M., Eggels, P.G., van Duin, R., de Goede, H.P., 1992. Environmental Life Cycle Assessment of Products. Guide and Backgrounds. CML, Leiden University, Leiden, The Netherlands. ISO14040, 1997. Environmental Management – Life Cycle Assessment – Principles and Framework. ISO14041, 1998. Environmental Management – Life Cycle Assessment – Goal and Scope Definition and Inventory Analysis. ISO14042, 2000. Environmental Management – Life Cycle Assessment – Life Cycle Impact Assessment. Johansson, M., 2005. Life Cycle Assessment of Fossil and Bio Based Materials for 3D Shell Applications – Material Eco-Profiles and Example With a Blow Moulded Clear Rigid Packaging – Assignment, Stockholm. Jolliet, O., Farago, S., Cotting, K., Drexler, C., 1994. Life cycle analysis of biodegradable packing materials: the case of popcorn. Agric. Ecosyst. Environ. 49, 253–266. Jolly, M., Jayaraman, K., 2006. Manufacturing flax fibre-reinforced polyproplene composites by hot-pressing. Int. J. Mod. Phys. B 20–25 (26–27), 4601–4606. Ong, S.K., Koh, T.H., Nee, A.Y.C., 1999. Development of a semi-quantitative pre-LCA tool. J. Mater. Process. Technol. 89–90, 574–582. Ong, S.K., Koh, T.H., Nee, A.Y.C., 2001. Assessing the environmental impact of materials processing techniques using an analytical hierarchy process method. J. Mater. Process. Technol. 113 (1–3), 424–431. Pervaiz, M., Sain, M.M., 2002. Carbon storage potential in natural fiber composites. Res. Conserv. Recycl. 39, 325–340. Schmidt, W.P., Beyer, H.M., 1998. Life Cycle Study on A Natural Fiber Reinforced Component. SAE Technical Paper 982195. Segetin, M., Jayaraman, K., Xu, X., 2007. Harakeke reinforcement of soil-cement building materials: manufacturability and properties. Build. Environ. 42, 3066–3079. SimaPro, PRe´ Consultants bv, Plotterweg 12, 3821 BB Amersfoort, The Netherlands, 2006. Sokovic, M., Mijanovic, K., 2001. Ecological aspects of the cutting fluids and its influence on quantifiable parameters of the cutting processes. J. Mater. Process. Technol. 109 (1–2), 181–189. Tan, X.C., Liu, F., Cao, H.J., Zhang, H., 2002. A decision-making framework model of cutting fluid selection for green manufacturing and a case study. J. Mater. Process. Technol. 129 (1–3), 467–470. van Houts, J., Bhattacharyya, D., Jayaraman, K., 1997. Mechanical properties of natural fibre-reinforced thermoplastic components. In: Ferguson, W.G., Gao, W. (Eds.), Proceedings of an International Conference on Advanced Materials Development, Performance Evaluation and Applications. The University of Auckland, New Zealand, July 14–15, 1997, pp. 477–482. Wotzel, K., Wirth, R., Flake, R., 1997. Life cycle studies on hemp fibre reinforced components and ABS for automotive parts. Angew. Macromol. Chem. 272 (4673), 121–127. Yeo, S.H., Neo, K.G., 1998. Inclusion of environmental performance for decision making of welding processes. J. Mater. Process. Technol. 82 (1–3), 78–88.
journal homepage: www.elsevier.com/locate/jmatprotec
Life cycle assessment of wood-fibre-reinforced polypropylene composites Xun Xu a,∗ , Krishnan Jayaraman a , Caroline Morin b , Nicolas Pecqueux b a
Department of Mechanical Engineering, University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand b Institut Francais de Mecanique Avancee (IFMA), Campus de Clermont-Ferrand les C´ezeaux, BP 265, 63175 Aubiere Cedex, France
a r t i c l e
i n f o
a b s t r a c t
Article history:
Composites of polymers reinforced with natural fibres have received increasing attention.
Received 13 February 2007
Natural fibres such as sisal, flax, jute and wood-fibres possess good reinforcing capabil-
Received in revised form
ity when properly compounded with polymers. These natural fibre-reinforced composites
22 June 2007
find a wide array of applications in the building and construction industry and the auto-
Accepted 27 June 2007
mobile industry. The use of natural fibres in composite materials does not automatically make it a “sustainable material”, i.e. “natural” may not necessarily equal “environment friendly”. The literature in the field of natural fibre-reinforced composites with respect to
Keywords:
their environmental standing is reviewed in this paper. A life cycle assessment has been
Wood-fibre
carried out for wood-fibre-reinforced polypropylene composite preforms produced by com-
Polypropylene
pression moulding in comparison with those of polypropylene. Three levels of fibre contents,
Composite
10%, 30% and 50% by mass, have been used. The level of environmental impact caused by
Life cycle assessment
transportation is also studied. This study introduces a new term called “material service
Natural fibre composite
density”, which is defined as the volume of material satisfying a specific strength requirement (tensile strength in this study). The rationale behind this is that specific volumes of different materials are required to withstand a given mechanical load (tensile load in this case). Comparison of the material service density for two materials: wood-fibre-reinforced composite and polypropylene are conducted. The results showed that when material service density is used as the functional unit, wood-fibre-reinforced composite demonstrated superior environmental friendliness compared to polypropylene. © 2007 Elsevier B.V. All rights reserved.
1.
Introduction
Over the last decade, composites of polymers reinforced by natural fibres have received increased attention. Natural fibres such as sisal, flax, jute and wood-fibres possess good reinforcing capability when properly compounded with polymers. The advantages of bio-fibres over synthetic fibres such as glass fibres are low cost, low density, renewability, favourable
∗
Corresponding author. Tel.: +64 9 373 7599; fax: +64 9 373 7479. E-mail address: [email protected] (X. Xu). 0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.06.087
values of specific strength and specific modulus, excellent chemical resistance and significant processing benefits which require minor changes to equipment. Thermoplastic polymers, such as high-density polyethylene and polypropylene, possess shorter manufacturing cycle times and reprocessability despite problems with high viscosities and poor fibre wetting. The renewability of natural fibres and the recyclablity of thermoplastic polymers provide an attractive eco-friendly
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
169
Fig. 1 – Natural fibres used for reinforcement.
quality to the resulting natural fibre-reinforced thermoplastic composite materials. Natural fibres can be classified into six types as shown in Fig. 1 (Bos, 2004). Natural fibre-reinforced thermoset and thermoplastic composites have found a wide array of applications in the building and construction industry in products such as door and window frames, decking material, railings for parapet walls and furniture sections, and the automobile industry in items such as door panels, seat backs, headliners, package trays, dashboards and trunk liners. Economics and other related factors in many developing countries, where natural fibres are abundant, demand scientists and engineers to apply appropriate technology to utilise these natural fibres as effectively and economically as possible to produce good quality fibre-reinforced polymer composites for housing and other needs (Segetin et al., 2007). The use of natural fibres in composite materials does not automatically make it a “sustainable material”, i.e. “natural” may not necessarily equal “environment friendly”. A better evaluation of the fundamental loops and processes of the entire life cycle of a material, such as the stages of extraction, use and disposal is necessary to make a judgment about the environmental characteristics of the material. Life cycle assessment (LCA) is a tool specifically developed for assessing the overall environmental burden of a product. The results can be used to optimize the environmental performance of a single product (eco-design) or to optimize the environmental performance of a company. Common categories of assessed damages in LCA are global warming (greenhouse gases), acidification, summersmog, ozone layer depletion, eutrophication, ecotoxic and anthropotoxic pollutants. The LCA method entails four parts (ISO14040, 1997; ISO14041, 1998; ISO14042, 2000): • Goal definition defines the aim and the scope of the study as well as the function and the functional unit of the studied product. • Life cycle inventory lists pollutant emissions and consumption of resources per functional unit. • Life cycle impact assessment classifies and evaluates the environmental impact of the pollutants emitted during the life cycle. • Life cycle interpretation allows one to interpret the results and to estimate the uncertainties. In the case of sustainable biomass, it is possible that far more material may have been extracted and translocated than
what is actually used in making the end product. An optimal material technology has, therefore, to consider resource consumption and the amount and the quality of waste material during the entire life cycle. These days however, the choice of material is still largely motivated by economic and mechanical criteria. The remaining text first reviews some of the literature concerning LCA performed on natural fibre-reinforced composites. The main body of the paper describes the LCA performed on a natural fibre- (i.e. wood-fibre) reinforced polypropylene composite in the context of the local (New Zealand) situation.
2.
Literature review
LCA allows us to understand the real environmental impact of a product, especially in the location where it is produced. Jolliet et al. (1994) pointed out when concluding their study on biomaterials, that “environment friendly” is different from “natural”. “Material service density”, defined as mass of material satisfying service requirements, is in fact a key factor for both technological and environmental optimization, especially in the case of long distance transport. LCA has long been associated with different material processing technologies and their end results. Ong et al. developed a semi-quantitative pre-LCA tool for assessing the environmental impacts of the production of a printer (Ong et al., 1999, 2001). Most of the research work seems to have focused on development of an effective means of assessing the environmental impact for different types of cutting fluids (Sokovic and Mijanovic, 2001; Alves and de Oliveira, 2006; Tan et al., 2002). Some effort has been spared on LCA for manufacturing processes such as cold rolling production (English et al., 2006) and welding processes (Yeo and Neo, 1998). There is limited research reported on LCA for composite materials and their products. De Vegt and Haije (1997) compared three reinforced composite rotor blades of a wind energy converter, flax fibre-reinforced epoxy, carbon fibre-reinforced epoxy and glass fibre-reinforced polyester. The LCA results gave a better score to flax fibre-reinforced composite (1.85 points1 ) against 2.4 points for the other two materials. They used a simplified LCA method called “matrix method”. It used
1 The Eco-indicator 99 single value expressing impact in three safeguard areas: damage to human health and the ecosystem and depletion of resources.
170
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Table 1 – Example for the “matrix method” (De Vegt and Haije, 1997) LCA phase
Considerations
Rotor-blade Flax fibre
Carbon fibre
Glass fibre
0
–
–
Production
Energy requirement
Use
Longevity, energy consumption, maintenance
0
0
0
Disposal
Landfill, combustion, recycling
0
0
0
0
1
1
Total
a table with the materials studied in columns and the different phases in rows (Table 1). Zero, pluses and minuses are entered in the cell and the totals are summed at the bottom. Though rough and more subjective, it can help to decide if a new material clearly outweighs the current one. Hansen et al. conducted a comparative LCA for two interior side panels of an Audi A3 (flax–jute reinforced epoxy and acryl-nitrile butadiene styrene copolymer also known as ABS) (Hansen et al., 2000). Major energy consumption happens during the use phase, i.e. fuel consumption which represents 80% of the total energy for manufacture, use and disposal of a car. As a result, the natural fibre composite side panel, as compared to the polymer panel, is ecologically preferable considering material, energy flows and emissions. Apparently, the utility phase of a car reveals substantial ecological advantages due to the weight difference. ` Corbiere-Nicollier et al. carried out LCAs for transport pallets made from glass fibre-reinforced PP, and China reed (CR) ` fibre-reinforced PP (Corbiere-Nicollier et al., 2001). The CR pallet consumes significantly less primary non-renewable energy. The strong primary non-renewable energy reduction for CR is attributed to three factors: (a) substitution of energy intensive glass fibre production by the low energy natural fibre production; (b) indirect reduction in the use of polypropylene linked to the higher proportion of China reed fibres used; (c) reduced pallet weight, which reduces fuel consumption during transport. The same study reports a net bonus for the incineration of PP of 21.5 MJ/kg and of 8.3 MJ/kg for natural fibre (China reed in this case). Glass fibres cost energy, 1.7 MJ/kg, during incineration and add negatively to the total Eco-indicator. For the natural fibre-reinforced composite part this means that about 25% of the energy costs of the production of the part are won back by incineration. For the glass reinforced part, which costs almost twice as much energy to produce in the first place, around 13% of the energy costs are won back by incineration. It was concluded that an environmental advantage of about 30% can be had due to the use of the natural fibre-reinforced material and a significant reduction of energy consumption due to weight saving during the use phase. Finally, use of China reed fibre as reinforcement in plastics proves advantageous from an ecological point of view, only if the CR pallet has a minimum lifetime of 3 years. Schmidt and Beyer conducted simplified LCAs for two designs of an insulation component in a Ford car (Schmidt
et al., 1998). One component is made of polymer reinforced by glass fibres, and the other is reinforced by hemp fibres (30% weight). The results of this study were only presented in the form of benefit values between natural fibre and glass fibre component. Thus, the natural fibre component requires 88.9 MJ less of the total energy demand. Looking at the emissions, the natural fibre component is also economic in that 8.18 kg of CO2 emissions, 0.0564 kg of SO2 emissions, 0.002 kg of phosphate emissions and 0.018 kg of nitrate emissions can be avoided. LCA based on the three phases as in the above-discussed cases, is obviously the closest to reality. Due to weight advantage, it seems to be a common phenomenon with natural fibre-reinforced composites that the longer a product life is, the more significant the environmental benefits. In a study on flax fibre-reinforced composites (Bos, 2004), an advantage is seen during the production phase, but benefits are more than obvious during the use phase because of its weight saving. This echoes the discussion on longevity of a product. In this research, the composites are made from matrices (epoxy resin, unsaturated polyester resin and polypropylene) and combined with either flax or glass fibres in different amounts (20%, 40% and 60%). The analysis also concluded that the mechanical properties are determined by the fibre, whereas the environmental impact is mainly related to the matrix. Cinar analysed the environmental impact of wood panels manufactured in Turkey (Cinar, 2005). LCA was applied to different kinds of wood-based panels, surface and edge treatments, and their respective manufacturing processes. According to the results, standard particleboard had an environmental impact lower than standard fibreboard (72%
Fig. 2 – Composite preform production.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
171
Fig. 3 – Process of creating a composite preform.
improvement). For surface and edge finishes, a low-density laminate is preferred to a high-density laminate (36% improvement). Wotzel et al. studied only the component manufacturing stage of an Audi A3 panel made from a hemp fibre epoxy composite (Wotzel et al., 1997). It was found that the natural fibre component uses 45% less energy than its alternative made of ABS co-polymer. However, water emissions of nitrates and phosphates, and nitrogen oxide (NOx) emissions to air are higher as a result of fertilizer applications in hemp cultivation. Overall Eco-indicator point scores are about 8% less for the hemp-fibre epoxy composite. Not surprisingly, the researchers found the weight saving for natural fibre-reinforced panels adds further benefits. In a study comparing hemp fibre mat thermoplastic with glass fibre composite (polypropylene is used as matrix), a significant energy savings of 60% per tonne of product by using natural fibre reinforcements can be expected through the following means (Pervaiz and Sain, 2002): (a) reducing use of PP by using higher proportion of natural fibres; (b) actual substitution of high-energy consuming glass fibres; (c) low weight of natural fibre composites; (d) saving in land filling efforts. Moreover, replacing even 20–25% glass fibre plastics with natural fibre composites can make a lot of difference for industrialized states, to curtail not only greenhouse gas emission but also to claim ‘carbon credit’ for these fibres.
Fig. 4 – Energy consumption of the vacuum oven.
Johansson studied a number of materials, including woodfibre-reinforced composite (Johansson, 2005). The suggested biocomposites, mixing PLA (polylactic acid) with pulps from wood-fibre, show promising environmental performance. This is mainly attributed to the use of wood pulp. The biocomposites shows a lower environmental impact than PLA and PET (polyethylene terphthalate) on most categories in both the CML (Centre of Environmental Science Leiden – Centruum voor Milieukunde Leiden) (Heijungs et al., 1992) and Ecoindicator methods. It combines the physical properties of a plastic material and the relatively low environmental impact of the pulp. In summary, the environmental standing for natural fibre composites as compared to their counterparts, e.g. synthetic fibre composites and polymers is not as conclusive if only the production phase is considered. The situation improves with sufficient evidence when use phase is included in LCA. When this is the case, the longevity of the product introduces a “magnification” factor. Similar to the use phase, the disposal phase also improves the environmental standing by giving back some energy and saving landfill space for example. Based on these findings, it seems that LCA for the production phase may hold the key to the final environmental standing of natural fibre composites. Any results that are at least not inferior to the compared materials will almost give it a favourable score in environmental terms. The following study aims to ascertain the environmental standing of wood-fibre-reinforced polypropylene composites by conducting an LCA for the production phase only.
Fig. 5 – Energy consumption of the hydraulic heated press.
172
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
from the accompanying Australian LCA database (SimaPro, 2006).
3.2.
Fig. 6 – Electricity generation by resource in New Zealand in 2004 (PJ).
3. LCA of wood-fibre-reinforced polypropylene composite 3.1.
Materials
Composite preforms are made of polypropylene and woodfibres. Polypropylene is originally in the form of granulated powder. The length of the fibres varies from 1 to 4 mm, and applied when composite sheets are made, with no particular orientation or patterns. The composite preform can have three or five layers (Jolly and Jayaraman, 2006), depending on the thickness of the preform. In this study, 2-mm sheets are considered, therefore a three-layered structure is adopted, i.e. one layer of fibre sandwiched between two sheets of PP (Fig. 2). The sheet has the size of 127 mm × 127 mm (5 in. × 5 in.). Fig. 3 shows the process of creating wood-fibre-reinforced composite preforms. The figure also defines the boundary of the LCA in this study.
Scope and goal
Natural fibre composite preforms are the common “intermediate stage” materials from which different products can be made. This study analyses wood-fibre composite preforms. While this gives a well-defined scope for LCA from the product fabrication point of view, two other factors also provide justification: (1) the situation improves with sufficient evidence when use phase is included, and (2) its recycling (minus disassembly) processes tend to be less variational. This study introduces a new term called “material service density”, which is defined as the volume of material satisfying a specific strength requirement (tensile strength in this study). The rationale behind this is that specific volumes of different materials are required to withstand a given mechanical load (tensile load in this case). Two sets of LCA are conducted: • Comparison of composites with three levels of fibre contents: 10%, 30% and 50% (with and without transportation included). • Comparison of the material service density for two materials: wood-fibre-reinforced composite and polypropylene. Polypropylene is sourced from Australia by sea and woodfibre from Rotorua, New Zealand. The preform sheets are made in a factory in Auckland. SimaPro software system has been used for LCA; the inventory data are primarily extracted
3.3.
Inventory
3.3.1.
Sources and production of wood-fibre
Wood-fibres usually come from two different sources: roundwood (debarked wood, logging residues and thinning) and industrial wood residues (sawdust, shavings, offcuts and slabs). This study considers debarked wood as the source of the wood-fibre. The debarked logs are chipped into pieces of 20 mm × 20 mm × 8 mm dimension using hammer mills or drum chippers in its “primary breakdown;” the energy used for the “primary breakdown” is known to be 2000–3000 kWh/t. Moreover, for the chipping process, 2 kg of water per tonne of wood is used. Chipping is followed by the “secondary breakdown,” also called the “refining” process, which extracts the fibres from the chips. Thermo-mechanical pulping has been widely used; it involves pre-steaming of chips for a short period before they are refined in a pressurised container. Mechanical pulping processes consume a large amount of electrical energy and water. However, they also yield a good amount of fibre, e.g. 80–90% recovery of total fibre. Mechanical pulping processes are cheaper to operate than more sophisticated chemical-based systems. There are also fewer environmental issues such as chemical contamination of sites and unpleasant smells. The secondary breakdown is achieved through a pressurised disc refiner; the energy consumption for this secondary breakdown
Fig. 7 – New Zealand net electricity generation and CO2 emissions in 2004.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Fig. 8 – New Zealand net electricity generation in 2004.
is estimated to be 250–400 kWh/t of bone-dry softwood fibres and somewhat less for hardwood fibres.
3.3.2.
Sources and production of polypropylene (PP)
PP produced in Australia is considered in this study; this takes into account three different PP plants, Kemcor, Montell-Clyde and Montell-Geelong, each having a market share in Australia of 19%, 44% and 37%, respectively. Since the PP considered is produced in Australia, shipping is also considered according to the functional unit. A distance of 1200 km is used as the average distance from the three plants to Sydney; the road trip by truck is assumed to be of 50% efficiency (one trip full, the return empty). The sea distance from Sydney to Auckland is taken to be 2150 km. The same 50% efficiency is assumed for land transport from Ports of Auckland to the factory where the preforms are made over a distance of 50 km. The database does not include the characteristics of transportation in NZ, so it is assumed that a 30 t truck has the same impact in NZ as in Australia. PP in granular form is considered to improve the adhesion with the fibres. This means that additional energy is consumed in conversion to the sheet form.
173
Fig. 9 – New Zealand CO2 emissions from combustion fuel type in 2004.
volume of fibres placed inside the chamber and (3) the heat loss. Maximum energy usage can be assured if the chamber is filled up with fibres. Therefore, the following assumptions are made: Working temperature: 90 ◦ C. Maximum power (600 W) to pre-heat the chamber (25 min). Power down to 20% of maximum power over next 25 min. Use the thermal inertia to reach 90 ◦ C at around 75 min mark. • Fibres are placed in the oven at the 75 min mark. • Use 20% of maximum power to maintain the temperature for the entire duration of the process.
• • • •
The energy consumption of the oven to dry the fibres corresponds to the area under the curve as shown in Fig. 4. Considering 6 h drying after the stabilization of temperature and one batch per day, the total energy that the oven uses is 25 × 600 + 25 × ((600 − 120)/2) + 25 × 120 × 2 + 6 × 120 60 = 1.17 kWh
3.3.3.
Fabrication of composite performs
During normal storage, the moisture content of the woodfibres increases; this leads to poor mechanical characteristics when used to make preforms. Therefore, fibre drying is always the first step. For this study, a common vacuum oven with an inside chamber of 19,664 cm3 (0.7 ft3 ) is used. Considering the common use, fibres need to be in the oven for 6 h at 90 ◦ C and a pressure of 0.8355 bar (25 in./Hg). Three factors are to be considered: (1) the energy needed to pre-heat the whole chamber to a certain temperature, (2) the
A manual hydraulic heated press (Carver press no. 4386 Model CH – electrical consumption: 1400 W, 230 V ac, 7 A) is used to produce the preforms. The energy spent by the operator to apply the pressure on the platens is not considered in this study. For information, this pressure is around 6.25 bar. Like the vacuum oven, efficiency coefficient, thermal loss, etc. are difficult to obtain, so the same method is used to calculate the amount of energy used. The two moulds are heated from a room temperature of 20 ◦ C. This phase takes 30 min
Fig. 10 – Average electricity in New Zealand.
174
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
Fig. 11 – SimaPro model for composite perform production.
and the Carver system uses thermal inertia in the last 5 min to reach the required working temperature, 200 ◦ C. The two Teflon sheets, the fibre mat and the two PP sheets are put into the moulds at the 35 min mark. The sheet is pressed down for nearly 5 min before it is taken out to set. It is assumed that 90 sheets are produced at each power-up of the press. The process operation regime is shown in Fig. 5. The total energy consumption for making 90 sheets of the composites can be calculated as follows: 1400 × 25 +
(1400 − 280) × 5 + 280 × 5 × 2 + 280 × 5 × 90 2
New Zealand energy profile. As shown in Fig. 6, New Zealand electricity comes from different sources. Fig. 7 (Dang and Cowie, 2006) shows the electricity generated through different sources and the CO2 emissions for each. It is clear that hydro and fuels represent two contrasting resources or power generation in New Zealand. Figs. 8 and 9 show the total electricity generation breakdown, in terms of percentages, of each natural source, and total CO2 emissions from the combustion type of energy sources (Dang and Cowie, 2006). Based on the values in Figs. 6 and 7, an “average electricity/NZ” entry can be created in SimaPro (2006) (Fig. 10).
= 166, 600 Wmin = 2.78 kWh = 10 MJ
3.3.4.
Energy profile
As the Australian database does not contain NZ energy profile, the New Zealand Energy in Brief for year 2004 published by the New Zealand Ministry of Economic Development in March 2006 (Dang and Cowie, 2006) has been used to create the
Fig. 12 – Comparison of the composite (30% fibre) and the PP sheet on different categories.
3.4.
Assessment
3.4.1.
Characterisation
In SimaPro, the substances that contribute to an impact category are multiplied with a characterisation factor that expresses the relative contribution of the substance towards
Fig. 13 – Weighting effect on the composite and PP sheets.
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
the impact category. Therefore, the characterisation factor can be seen as an equivalence factor. For example, the characterisation factor for CO2 in the impact category, climate change, can be equal to 1, while the characterisation factor of methane can be 21. This means release of 1 kg methane causes the same amount of climate change as 21 kg of CO2 does. In other words, the climate change caused by methane is 21 times more sever than that by CO2 . It is also possible to define a specific characterisation factor for each subcompartment of a substance. This is only necessary when a particular subcompartment of a substance is of interest in an LCA.
3.4.2.
Normalization
Many methods allow the impact category indicator results to be compared by a reference or normal value. This means the impact category is divided by a reference. The reference may be chosen freely, but often the average yearly environmental load in a country or continent, divided by the number of inhabitants is used as the reference. After normalization the impact category indicators all get the same unit, e.g. 1 year, which makes it easier to compare them. Normalization may also be applied on characterisation and damage assessment results, depending on the structure chosen for a particular method.
3.4.3.
Weighting
Some methods allow weighting across impact categories. This means the impact or damage category indicator results are multiplied by the weighting factors, and are added to form a total score. Weighting can be applied on normalized or not normalized scores, such as environmental priority system (EPS) which does not have a normalization step. It is also possible to stop at the normalization step as in the Centre of Environmental Science Leiden method (CML 92).
3.4.4.
Assessment methods
Eco-indicator 99 is used as the assessment method. It assesses the environmental impact in the following 11 categories: • • • • • • • • • • •
carcinogens; respiratory organics; respiratory inorganics; climate change; radiation; ozone layer; ecotoxicity; acidification/eutrophication; land use; minerals; fossil fuels.
175
• EQ: ecosystem quality (unit: PDF × m2 yr; where PDF stands for potentially disappeared fraction of plant species; m2 stands for the area size and yr (year) stands for the time period to obtain the damage). • R: resources (unit: MJ surplus energy; additional energy requirement to compensate lower future ore grade). Eco-indicator 99 has a damage assessment step. The impact category indicator results that are calculated in the characterisation phase, are added to form damage categories. Addition without weighting is justified here because all impact categories that refer to the same damage type (like human health) have the same unit (for instance DALY). This procedure can also be interpreted as grouping. The damage categories (not the impact categories) are normalised on a European level (damage caused by one European per year), mostly based on year 1993 as the base year, with some updates for the most important emissions. Please note that the normalization set is dependent on the perspective chosen.
3.4.5.
Assessment results and discussions
Three sets of comparative assessments have been carried out using SimaPro involving three different levels of fibre contents: 10%, 30% and 50% by mass. The same is done for situations with and without transportation taken into account. To save space, only the results involving 30% of fibre content are graphed (Figs. 12–14). It is obvious that use of fibres in the composite leads to direct reduction in environmental impact. This is proportionate to the amount of fibre used. When transportation is considered, i.e. the transportation of fibres inside New Zealand and PP from Australia to New Zealand, an 8% increase in impact is witnessed. The above analysis is effectively based on the mass functional unit, i.e. the same mass is assumed when comparing the wood-fibre-reinforced PP composite and PP. In actual engineering applications, materials are used to serve certain strength requirements, e.g. tensile strength. Other times, the same volume is needed to serve a functional purpose. In both cases, the environmental benefit exhibited by the wood-fibre-reinforced PP composite will be further “magnified”.
Fig. 11 shows the SimaPro model for creating the composite preforms from polypropylene and wood-fibres. In the Eco-indicator 99 method, normalization and weighting are performed at damage category level (endpoint level in ISO terminology). There are three damage categories: • HH: human health (unit: DALY = disability adjusted life years; this means different disability caused by diseases are weighted).
Fig. 14 – Global comparison between the composite and the PP sheets.
176
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
3.4.6.
Use of volume functional unit
When a similar volume is required in making a particular product, the physical densities of both the composite and PP come into play. It is obvious that the wood-fibre-reinforced PP composite will have lower density than PP and it is dependent on the density of the (dried) wood-fibre. Assume f and P are the densities of wood-fibre and PP, respectively. The density of wood-fibre-reinforced PP composite (c ) with v percentage of fibre in volume, or m (m = 30% in this case) percentage of fibre in mass can be obtained as follows: c = f × v + P × (1 − v) = P + (f − P )v (kg/m3 )
=
mc = Ac × h × c
m/f (m/f ) + ((1 − m)/P )
and
mP = AP × h × P
The additional PP in mass PPm , in percentage terms, can be calculated as PPm =
(1)
The moisture level varies a great deal with wood-fibres. This is also true even with dried fibres. Determination of its accurate density value is therefore not an easy task. According to Bowis (Bowis, 1997), one can assume, f = 400 kg/m3 . Given the PP’s density P = 900 kg/m3 , the ratio of fibre in volume (v) can be calculated as Wood-fibre volume ratio : v =
density of the composite (c = 650 kg/m3 ) and that of PP (P = 900 kg/m3 ). Assuming h is the third dimension, e.g. height of the component, the required mass of the composite (mc ) and that of PP (mP ) can be expressed as
=
mP − mc AP × h × P − Ac × h × c %= % mc Ac × h × c AP × P − Ac × c % Ac × c
(5)
According to Eq. (4) PPm =
AP × P − (P /c )AP × c c × P − P × c %= % P × c (P /c )AP × c
(6)
The literature (van Houts et al., 1997) suggested that the tensile strength of wood-fibre-reinforced PP composite with 30% of fibre mass is around 30 MPa and that of PP, 23 MPa. The above formula can be expressed as
0.3/400 = 0.5 (0.3/400) + (0.7/900)
PPm =
c × P − P × c 30 × 900 − 23 × 650 % = 81% %= P × c 23 × 650
This means that for a composite of 30% fibre and 70% PP by mass, the volumes of fibre and PP are nearly the same. The density of the wood-fibre-reinforced PP composite with 30% of fibre mass can also be calculated as
This means that to withstand the same tensile load, 81% more of PP in mass is needed than if the composite is used.
c = P + (f − P )v = 900 + (400 − 900) × 0.5 = 650 (kg/m3 )
4.
3.4.7. “Material service density” for satisfying the strength requirement When both wood-fibre-reinforced PP composite and PP products are designed to suit a particular strength requirement, less wood-fibre-reinforced PP composite (in both volume and mass) is actually needed than PP. This is based on the fact that the former has lower density as well as superior tensile strength than those of the later. Assume c is the tensile strength for the composite material and P the tensile strength for PP, then c =
F Ac
(2)
P =
F AP
(3)
where F is the force applied and Ac and AP are the area of crosssection for the composite and PP component, respectively. Therefore, Ac =
P AP c
(4)
This means that to meet the same tensile strength requirement, one would need to use (1 − P / c )% more volume of PP than that of the composite if composite is used. When volume is translated into mass, such an increase is further “amplified” due to the difference between the
Conclusions
There has been little literature on life cycle assessment on natural fibre-reinforced composite although scientific research on this type of materials has been on a steady rise. This is perhaps attributed to the drive toward using environmentally friendly materials. However, the literature shows a non-conclusive environmental effect when only the production phase of such composites is studied. During the cultivation stage, the use of pesticides and other types of chemical products can give a negative impact on the environment. On the brighter side, the use and the disposal phase of such composites demonstrated a clear advantage from the environmental point of view. Natural fibre-reinforced composites are generally lighter, which helps save fuel during transportation. At the disposal phase, more energy can be claimed back through processes such as incineration. The life cycle assessment on the wood-fibrereinforced polypropylene composite, locally manufactured in New Zealand, with PP imported from Australia, revealed some results similar to those discussed above. Yet, some interesting discoveries were made. • Transportation of fibres and PP does not have a significant effect. • In the composite, the PP content is the dominant factor on environmental damages; use of wood-fibres in the composite (e.g. 30%) has rather a mild effect. • Environmental standing of the wood-fibre-reinforced polypropylene composite further improves in the following situations:
j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 1 9 8 ( 2 0 0 8 ) 168–177
◦ When a similar volume is required in making a particular product, the environmental standing of the composite further improves. This is due to the fact that the composite has lower density than PP. For a composite of 30% fibre and 70% PP, the density value is 650 kg/m3 as compared to that of PP being 900 kg/m3 . ◦ When both wood-fibre-reinforced PP composite and PP products are designed to suit a particular tensile strength requirement, the environmental standing of the composite also improves. This is because less composite (in both volume and mass terms) is actually needed than is PP. This is based on the fact that the former has superior tensile strength as well as lower density. To withstand the same tensile load, the same composite (30% fibre and 70% PP) only needs less than a quarter of PP in mass if PP was used. The study is based on the preform sheets, which is an “intermediate material” for further making final products. Therefore, this LCA was for a partial, but a major portion of, production phase. In a way, the study confirmed a hypothesis that if the production stage of the wood-fibre-reinforced PP composite exhibits a better environmental standing than that of PP, one can safely assume that the entire life cycle of the wood-fibre-reinforced PP composite possesses a better environmental standing than that of PP.
references
Alves, S.M., de Oliveira, J.F.G., 2006. Development of new cutting fluid for grinding process adjusting mechanical performance and environmental impact. J. Mater. Process. Technol. 179 (1–3), 185–189. Bos, H., 2004. The Potential of Flax Fibres as Reinforcement for Composite Materials. Eindhoven University of Technology. Thesis available on http://www.tue.nl/bib. Bowis, M.E., 1997. Mechanical Properties and Formability of HTMP Wood-Fibre Composite-Polypropylene Composite Sheets. PhD Thesis. Department of Mechanical Engineering, University of Auckland, New Zealand. Cinar, H., 2005. Eco-design and furniture: environmental impacts of wood-based panels, surface and edge finishes. For. Prod. J. 55 (11), 27–33. ` Corbiere-Nicollier, T., Gfeller, L.B., Lundquist, L., Leterrier, Y., Manson, J-A.E., Jolliet, O., 2001. Life cycle assessment of biofibres replacing glass fibres as reinforcement in plastics—resources. Conserv. Recycl. 33, 267–287. Dang, H., Cowie, P., 2006. New Zealand Energy in Brief March 2006, ISSN 1177-2824 (http://www.med.govt.nz/energy/info/). De Vegt, O.M., Haije, W.G., 1997. Comparative Environmental Life Cycle Assessment of Composite Materials—ECN-I-97-050. English, M., Castellucci, M., Mynors, D.J., 2006. Eco-efficiency of the cold roll formed product supply chain. J. Mater. Process. Technol. 177 (1–3). Proceedings of the 11th International Conference on Metal Forming, July 3, 2006, pp. 626–629. Hansen, A., Flake, M., Heilmann, J., Fleißner, T., Fischhaber, G., 2000. Life Cycle Studies of Renewable Raw Materials – Natural
177
Fibre Reinforced Component and a Varnish – Bio-Resource Hemp 2000, Wolfsburg, September 13–16, 2000. ´ J., Huppes, G., Lankreijer, R.M., Udo de Haes, Heijungs, R., Guinee, H.A., Wegener, S.A., Ansems, A.M.M., Eggels, P.G., van Duin, R., de Goede, H.P., 1992. Environmental Life Cycle Assessment of Products. Guide and Backgrounds. CML, Leiden University, Leiden, The Netherlands. ISO14040, 1997. Environmental Management – Life Cycle Assessment – Principles and Framework. ISO14041, 1998. Environmental Management – Life Cycle Assessment – Goal and Scope Definition and Inventory Analysis. ISO14042, 2000. Environmental Management – Life Cycle Assessment – Life Cycle Impact Assessment. Johansson, M., 2005. Life Cycle Assessment of Fossil and Bio Based Materials for 3D Shell Applications – Material Eco-Profiles and Example With a Blow Moulded Clear Rigid Packaging – Assignment, Stockholm. Jolliet, O., Farago, S., Cotting, K., Drexler, C., 1994. Life cycle analysis of biodegradable packing materials: the case of popcorn. Agric. Ecosyst. Environ. 49, 253–266. Jolly, M., Jayaraman, K., 2006. Manufacturing flax fibre-reinforced polyproplene composites by hot-pressing. Int. J. Mod. Phys. B 20–25 (26–27), 4601–4606. Ong, S.K., Koh, T.H., Nee, A.Y.C., 1999. Development of a semi-quantitative pre-LCA tool. J. Mater. Process. Technol. 89–90, 574–582. Ong, S.K., Koh, T.H., Nee, A.Y.C., 2001. Assessing the environmental impact of materials processing techniques using an analytical hierarchy process method. J. Mater. Process. Technol. 113 (1–3), 424–431. Pervaiz, M., Sain, M.M., 2002. Carbon storage potential in natural fiber composites. Res. Conserv. Recycl. 39, 325–340. Schmidt, W.P., Beyer, H.M., 1998. Life Cycle Study on A Natural Fiber Reinforced Component. SAE Technical Paper 982195. Segetin, M., Jayaraman, K., Xu, X., 2007. Harakeke reinforcement of soil-cement building materials: manufacturability and properties. Build. Environ. 42, 3066–3079. SimaPro, PRe´ Consultants bv, Plotterweg 12, 3821 BB Amersfoort, The Netherlands, 2006. Sokovic, M., Mijanovic, K., 2001. Ecological aspects of the cutting fluids and its influence on quantifiable parameters of the cutting processes. J. Mater. Process. Technol. 109 (1–2), 181–189. Tan, X.C., Liu, F., Cao, H.J., Zhang, H., 2002. A decision-making framework model of cutting fluid selection for green manufacturing and a case study. J. Mater. Process. Technol. 129 (1–3), 467–470. van Houts, J., Bhattacharyya, D., Jayaraman, K., 1997. Mechanical properties of natural fibre-reinforced thermoplastic components. In: Ferguson, W.G., Gao, W. (Eds.), Proceedings of an International Conference on Advanced Materials Development, Performance Evaluation and Applications. The University of Auckland, New Zealand, July 14–15, 1997, pp. 477–482. Wotzel, K., Wirth, R., Flake, R., 1997. Life cycle studies on hemp fibre reinforced components and ABS for automotive parts. Angew. Macromol. Chem. 272 (4673), 121–127. Yeo, S.H., Neo, K.G., 1998. Inclusion of environmental performance for decision making of welding processes. J. Mater. Process. Technol. 82 (1–3), 78–88.