Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics Duarte Almeida Integrated Master in Mechanical Engineering Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal [email protected] Abstract The use of biodegradable and compostable plastics based on renewable raw materials (R-BDP) has a rising interest derived from its particular characteristics. Currently, various R-BDPs are combined to improve some technical requirement of the final products, to open up new applications or to reduce costs. The specific use of renewable raw materials such as maize, potato, wheat and other carbohydrate sources as feed stocks for the production of R-BDPs is claimed to give the final products certain advantages in terms of reduced environmental impact. To assess the overall impact of the use of such materials, the economical, environmental and functional performance must be analysed on a life cycle approach. In this study a Life Cycle Engineering (LCE) model is developed to compare the economical, environmental and technical dimensions of performance for 4 different blends of R-BDPs when processed through injection moulding technology, following a material cradle-to-grave approach. Moreover, to understand the claimed advantages of these particular plastics, they are compared to a well-known common plastic, in the case, Polypropylene (PP). The proposed LCE model allows full comparison of the R-BDPs, supporting informed material selection decisions in a product design context. The aggregation of the 3 performance dimensions into a ternary decision space supports materials comparison and the identification of their „„best alternative domains‟‟. Keywords: Life Cycle Engineering, Life Cycle Cost, Life Cycle Assessment, Functional Assessment, Biodegradable Plastics, Injection Moulding.

1. Introduction The increasing environmental awareness of today‟s society has affected most of industrial processes and products. Plastic, which is one of the most versatile materials in the modern age, is widely used in many products throughout the world. However, its dramatic production increasing has focused public attention on a potentially huge environmental pollution problem that could persist for centuries, because of their extremely low degradability, to the expectable scarcity of landfill sites and to the growing levels of water and land pollution [1] [2]. Furthermore, as the great majority of plastics are still derived from fossil fuel resources, their rapid increase will put further pressure on the already limited non-renewable resources on earth. This new context of an environmentally conscious society has fostered the development of new solutions for plastics, with allegedly lower environmental impacts [3]. In fact, plastics derived from renewable raw materials (RRM) and in particular, biodegradable and compostable plastics derived from RRM (R-BDP) may serve as a promising solution to the overloaded landfills by diverting part of the volume of plastics to other means of waste management and, in most of the cases, by preserving nonrenewable resources [4]. These materials have been strongly developed driven by increasing concern in sustainable development, in the desire to reduce dependence upon finite resources and in changing policies and attitudes in waste management. However, it‟s crucial to understand the implications of the transition to these “greener” materials.

This study aims to compare several types of plastics made from RRM applied to products manufacturing by the injection moulding process. Moreover, to realize their level of performance they are compared to a well-known fossil origin plastic (FoP) and commonly used in that technological process; in the case, Polypropylene (PP). This performance evaluation assesses not only the environmental aspects, but also the economic and functional aspects, following a cradle-to-grave approach. Starch (STA) has been seen as a possible substitute for FoPs as it is both renewable and biodegradable. However, due to its water sensitivity and low mechanical properties, it‟s not suitable for many plastic products. One solution developed to overcome these limitations was to combine plasticized starch with another R-BDP, such as Polylactic Acid (PLA) [5]. PLA is currently one of the most promising R-BDPs, as some studies have found that PLA has comparable mechanical and physical properties to that of Polytethyleneterephtalate (PET) and Polystyrene (PS) [6], therefore being able to fulfil very different commercial applications [5]. Following this research area, this study aims to compare four different types of R-BDPs with different amounts of STA and PLA, considering a final product produced by injection moulding. The comparison, unlike most studies in the area regarding only environmental impacts, comprises also a comprehensive economical and functional performance analyses, within a Life Cycle Engineering (LCE) scope. Hence, it allows having an integrated view of the advantages and disadvantages of using these new materials regarding several dimensions of analysis. Being LCE a general methodology connecting several areas, it is necessary to 1

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics use different methods to evaluate the dimensions of analysis. As the aim is to analyse different materials of a generic product produced by injection moulding, it was considered the life cycle of the product comprising the stages from material production till the product end-of-life. The life cycle stages were analysed both in terms of economical performance, through Life Cycle Cost (LCC) method, and in terms of environmental evaluation, using Life Cycle Assessment (LCA). LCC objective is to cover the assessments of costs in all steps of the product‟s life cycle, including the costs that are not normally expressed in the product market price [7], such as costs incurred during the usage and disposal. LCC is essentially an evaluation tool in the sense that it gets on important metrics for choosing the most cost-effective solution from a series of alternatives [8]. Regarding LCA, it is a structured method to quantify potential environmental impacts of products or services over their full life cycle [9] [10], being therefore a valuable tool to provide designers with information on inputs, outputs and associated environmental impacts of a defined system [11]. Regarding the functional dimension of analysis, the proposed materials are compared taking into consideration its intrinsic characteristics and its correlations with the most important characteristics of a plastic part. Finally, instead of following the traditional approach of analysing the dimensions separately, the three dimensions of analysis were aggregated in a single analysis framework. The result is a more comprehensive view of the possible choices. The framework is a ternary diagram, in which the dimensions of analysis are represented in each axis. With this approach, the difficult task related to the materialization of the relative importance of the three dimensions into a set of weights is overcome. The use of ternary diagrams to support decisions has already been applied in other industrial frameworks [12]. Results from the global evaluation depend on assumptions taken during the study. Hence, a few sensibility analyses were made in order to assess the relevance of those assumptions in the global evaluation. These sensibility analyses were possible to do because of the flexibility of the developed models which permit varying input parameters and rapidly visualize its implications on the outputs, or final results. Therefore LCE may be an effective tool to compare RBDPs, since integrates different dimensions of performance throughout all life cycle stages. Data concerning the injection moulding process of the plastics in comparison, such as material properties, injection equipment characteristics, injection parameters and, parts‟ geometry and properties, was kindly provided by Eng. Pedro Teixeira, who made the injection and mechanical tests in the scope of his PhD thesis. All other kind of information used to make the analyses (like waste management practices or waste treatment options costs), because of the lack of sources availability, required exhausting efforts of research and continuous contacting with enterprises and entities in the business, to gather it. So, some values necessary to proceed with the analysis were assumed based in few, yet reliable, sources. After this introduction, it´s presented in Chapter 2 the study‟s Research Framework, such as the followed work plan, the

materials‟ characterization applied. In Chapter 3, the analyse the performance injection moulding process conclusions are presented.

and the life cycle models LCE approach it‟s applied to of R-BDPs in the plastics and finally on Chapter 4 the

2. Research Framework 2.1 Work methodology The first task was to investigate about R-BDPs insights as, characteristics, manufacturing technologies or typical applications. Also the study on LCE philosophy and in particular its application to material selection was made. Secondly, characterization of the work previously made was performed. Here, it was important to gather and understand all the information about the materials and their properties, about the plastic part into which these materials were transformed (samples) and about the injection moulding process. Then, and in order to compare the materials in a life cycle perspective, it became necessary to identify the life cycle stages for plastic material parts and in particular for R-BDP parts. In particular for the End of Life (EOL) stage, several possible EOL scenarios were defined based on literature research and experts knowledge. The fourth step was to collect all the necessary data to introduce in the developing life cycle models for costs and environmental impacts evaluation. Information regarding to the industrial environment, such as labour, equipment and facilities was collected in FAPIL, S.A. Data concerning the EOL stage, such as waste treatment processes‟ costs, was collected from companies in the business. Along and in continuous feedback with data collection, the development of the process based parametric models for cost and environmental analysis was done. The next step was to make the functional assessment analysis and integrate it with the economic and environmental dimensions, thus completing the LCE approach.

Fig. 1: Applied methodology

One of the advantages of using process based parametric models is their possibility to vary the inputs, making it possible to understand their sensitivity to different variables. Therefore and after the initial analysis 2

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics different considerations of production volume, EOL scenario and part‟s geometry, to evaluate how the costs and impacts would behave were tested. Finally, the results are presented and discussed.

2.2 Experimental data In this case study 4 R-BDP commercial materials were analysed. They are all based on Starch (STA) blended with Polylactic Acid (PLA) with different proportions (Tab. 1). The FoP chosen to compare with the R-BDPs was the Polypropylene (PP). The purpose of this research is to compare the different blends of R-BDPs applied to plastic parts obtained by injection moulding, so the focus is the material and not the product. However, the comparison of the materials following a life cycle perspective, demands to transform the materials into plastic parts, and according to its geometry and dimensions (Fig. 2 and Fig. 3), the injected samples into which the blends where injected, may very well be equivalent to a part made in R-BDP. Material

Manufacturer

10/90

Cabopol

40/60

Rodenburg Biopolymers

80/20

Cabopol

90/10 PP

Biotec Total Petrochemicals

Trade name Biomind C004 Solanyl 35F Biomind R006 Bioplast GS 2189

Melting point [⁰C]

MFI [g/10min]

1200

90

15-30

1280

140-145

13

80%PLA+20%STA

1250

130

20-40

90%PLA+10%STA

1300

130

20-40

-

905

165

25

Composition

Density 3 [kg/m ]

10%PLA+90%STA 40%PLA+60%STA

PPH 9020

Tab. 1: Injection materials properties [Source: manufactures]

Fig. 2: Sample for tensile tests (185x21x4 mm)

content of STA have bigger differences between injection and ejection temperatures , which demand longer time to cool down the part to a safe temperature of extraction, in order to avoid defective parts, in particular, burned parts. Therefore these materials need longer injection cycles than ones having smaller gaps between injection and ejection temperatures. Material

Inj. Press [bar]

Hold. Press [bar]

Inj. Temp [⁰C]

Warming time [sec]

Cycle time [sec]

Part mass [g]

Wastes [g/cycle]

Mat. input [g]

10/90

59.50

39.00

100

521.74

48

27.00

0.32

27.32

40/60

59.75

38.75

140

730.43

46

28.80

0.35

29.15

80/20

60.00

37.71

140

730.43

41

28.13

0.34

28.46

90/10

59.50

39.00

140

730.43

41

29.25

0.35

29.60

PP

30.92

19.92

230

1200.00

29

20.36

0.24

20.61

Tab. 2: Injection variables

2.3 LCE model The first stage of the LCE model proposed in this study (Fig. 4) is to define the boundaries of the problem under analysis and to collect specific data for material application and product life cycle. The next step is to evaluate individually the product from an economic, environmental and functional point of view. These evaluations use distinctive methods. Economical and environmental evaluations are performed from a life cycle perspective, using LCC and LCA respectively. Functional evaluation is performed using a Multiple Attributes Decision- Making (MADM) method and the Simple Additive Weighting (SAW) method, which allow a logical approach to fuzzy problems [13]. For each material and for each dimension of evaluation (functional, economic, and environmental) a single indicator is obtained, allowing the direct incorporation of the functional, economical and environmental performances into a multi-criteria decision problem.

Fig. 3: Sample for impact/flexion tests (132x13x6.5 mm)

Typically R-BDPs‟ parts have small dimensions and simple geometries, like a fork, a knife or even a toothbrush and thereby similar to those of the samples. Therefore and further on, the samples will be considered as parts representing a general product made in R-BDP material and with identical dimensions to the samples. In the scope of Eng. Pedro Teixeira‟s research, tensile, flexion and impact mechanical tests were made to the materials, which implied having samples with different geometries. Those mechanical tests are out of this research‟s scope. However, the same two samples were considered for this work, as if the two geometries were two components for a final product. Several tests varying the conditions of injection were made in order to establish the best injection parameters that assured acceptable quality of the injected samples. Among the injection parameters that permitted to obtain sound parts, it was chosen the ones that minimize the injection cycle time. The cycle time obtained as well as other injection variables are presented in Tab. 2. R-BDPs demand longer injection cycles compared to PP and in particular the R-BDPs with higher

Fig. 4: Overview of the LCE model

The final result is a global evaluation, presented in a ternary diagram, clearly showing the possible choices 3

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics according to the importance given to the three dimensions of analysis. This ternary materials selection diagram illustrates the „„best materials‟‟ for different criteria weights. In fact the ternary diagrams identify not only the best materials according to a set of weights attributed to functional, economic, and environmental dimensions, but also the range of weights of each „„best material‟‟.

perform the manufacturing process.

3. Application of the LCE approach to analyse the performance of R-BDPs in injection moulding process In this section the LCC and LCA life cycle models are applied to the selected plastic materials to obtain the economic and environmental analyses of these materials in a life cycle perspective. The aim of these analyses is to understand costs and environmental integrated impacts resulting from the choice of a particular plastic. Fig. 5: Plastic parts life cycle

3.1 Plastic parts life cycle stages Before applying the life cycle models it‟s necessary to define the plastics‟ life cycle with all the relevant data and key processes of each life cycle stage to use on the life cycle models. Fig. 5 represents the main stages of the plastic parts, from raw material acquisition to end of life. Bearing in mind the type of products on which the analyses are based on (disposable and of brief usage), the use stage will not be analysed since costs and environmental impacts caused by it can be neglected. Raw material acquisition is related to the corn growing and harvesting for the case of the R-BDPs and with the extraction of oil or natural gas for PP. Plastics processing stage concerns to the addition of additives to improve materials‟ properties. In the case, PLA is added to improve STA‟s water sensitivity and low mechanical properties and consequently enriching R-BDP blends. In the Plastic parts manufacturing stage it is considered an input flow of energy to manufacture the plastic parts. This energetic consumption promotes an outflow of emissions. There‟s also a mass stream input which has its origin in the previous stage of Plastics Processing. There may be also another mass stream input that comes from the process of plastics recycling, but only in the case of PP parts, as only PP parts may undergo a plastic recycling process. All the parts are manufactured by injection moulding process. Apart from the differences on the amounts of energy and mass necessary to produce each one, the process is the same, as well as the mould used to Scenarios Ideal (S1) st

1 interm. (S2) 2

nd

interm. (S3)

Worst (S4)

There are different waste treatment methods available for plastics at End of Life, being composting the preferred method for R-BDPs and mechanical recycling for PP, as they seem to be the best alternative, regarding the climate change potential, depletion of natural resources and energy demand [14]. Landfill appears as the worst disposal method for all plastics [4] [15]. In this study 4 different scenarios of disposal (Tab. 4) were assumed in order to assess the impacts on costs and on environment that a final disposal option has on the material life cycle. Some assumptions taken to perform the analyses are summarized in Tab. 3. Production volume Batch Inj. Mach. Energetic efficiency Injection process wastes Mould‟s setup time End of Life Scenario

200,000 units 25,000 units 80% 1.2% 30 min S1

Tab. 3: Assumptions taken to perform the analyses

3.2 Life Cycle Cost The global approach of the LCC model to each material‟s life cycle stage is illustrated in Fig. 6. At each one of the life cycle stages, the LCC model uses the parameters to perform a simplified life cycle inventory, considering only the relevant streams, crosses this information with costs databases and retrieves a total

Plastics

Collection

Process

Products

R-BDPs as BUW

Selective

Composting

Compost

PP as recyclabe

Selective (ecopoints)

Recycling

Recycled PP

R-BDPs as SUW

Undifferentiatted

Landfill

-

PP as recyclabe

Selective (ecopoints)

Recycling

Recycled PP

R-BDPs as BUW

Selective

Composting

Compost

PP as recyclable

Undifferentiatted

Landfill

-

All as SUW

Undifferentiatted

Landfill

-

Tab. 4: Final disposal options (BUW – Biodegradable Urban Waste; SUW – Solid Urban Waste)

4

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics stage cost. Gathering all stages it‟s possible to obtain the entire life cycle cost.

Fig. 6: LCC Model

The cost assessment of the Plastic parts manufacturing stage (Injection moulding) revealed that 10/90 is the most expensive material to produce, while in opposition, 80/20 and 90/10 present the lower production costs among the R-BDPs (Fig. 7). It also revealed PP presents a much lower production cost than R-BDPs. Despite of varying with the injection material, the injection moulding costs are pretty much equally distributed (Setup – 0%, Labour – 52%, Energy – 1%, Equipment – 47%) for every material, being the cost related with labour and equipment the most important and setup and energetic costs practically negligible. The reduction on every cost category, exception for energy is evident with the increase on PLA. The reduction on every cost category is evident with the increase of PLA composition in the R-BDP blends, since R-BDPs blends with higher composition of PLA have shorter injection cycle times, and for that require less labour and equipment time of utilization.

Fig. 7: Injection stage costs distribution

Fig. 8: Injection cycle time Vs. Injection and Raw material costs for 200,000 units

Equipment costs are directly related with its time of utilization and of course with its investment cost, but once

it was used the same machine on the injection of all materials, becomes of interest to analyse the machine‟s time with the injection costs. Fig. 8 shows that the injection cost is largely influenced by the injection cycle time, since materials with longer cycle times, present higher costs for this production volume. 10/90 has the longer injection cycle time and because of that is the one with higher production cost. Moreover, it‟s clear that greater concentrations of STA demand longer injection cycle times, so the more expensive parts to produce are the ones made of R-BDP materials with higher amount of STA, although being the less expensive R-BDPs to acquire. The total life cycle cost assessment will help to understand how these differences will contribute for the final cost of each material (Fig. 9).

Fig. 9: LCC results and costs distribution for 200,000 units

Results show that PP costs less than R-BDPs at all life cycle stages. In materials acquisition stage, 40/60 is the most economical material to acquire among the R-BDPs. Although it doesn‟t presenting the less consumption of material, it has the lowest cost per unit of mass. In the parts manufacturing stage – injection moulding – 80/20 and 90/10 have approximately the same production cost and are the most economical R-BDPs to produce, mainly due to its shorter injection cycle time that is reflected on the equipment and labour costs. When it comes to final disposal, R-BDPs present very similar costs, being 10/90 the most economical, once it requires less amount of material to deliver the 200,000 parts, nevertheless being these stage‟s costs practically insignificant. Mould production stage also takes only a minimal part of the final cost, for this annual production volume. At this point it is now possible to prove that the contribution of the injection moulding stage is the most relevant on the total life cycle cost, representing between 66% and 82% of the costs for all candidate plastics. The spending on raw material has proven to be the second most important cost category, representing between 19% and 28% for R-BDPs and 11% for PP. This difference may be explained by the initial lower cost of raw PP and by the recovering of material by means of process wastes recycling. In conclusion, the combination of a short cycle time of injection with an average material acquisition cost points out to 80/20 as the most economical R-BDP and 10/90 the least. The final costs also reveal that PP is around 40% more economical than the average of the R-BDPs.

5

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics

3.3 Life Cycle Assessment At this stage, a cradle to grave approach to assess the environmental impacts of the several candidate plastics is performed, using all data previously collected for the injected parts and considering an annual average production of 200,000 parts. The LCA Model (Fig. 10) is composed by two main stages: the account of the emissions produced and of the resources consumed during the product‟s life cycle (LCI), and the impact assessment of these emissions and consumptions (LCIA).

EOL waste management practices play an important role in the plastics‟ environmental performance. In a global analysis and for the chosen EOL scenario (S1), PP has smaller overall environmental impacts, mainly because of the avoided material that the recycling process permits [14], but also because of the increasing impacts on materials production caused by the growing presence of PLA on the R-BDPs composition. The very low presence of PLA on the 10/90 R-BDP turns it as the only R-BDP able to compete with PP in environmental impacts generated during the part‟s life cycle.

Fig. 11: LCA final results for 200,000 units (EOL S1) Fig. 10: LCA Model

The Emissions Data base indicated in Fig. 10 refers to the emissions produced in two separate ways: emissions generated on the production of raw materials and emissions generated on the production of each unit of energy consumed during each process. With all the emissions and resources consumptions aggregated into the impact categories, these are then weighted following a hierarchic/average (H/A) perspective, which is a moderate perspective generally accepted by the scientific community, attributing 40–40–20% of weight to the three considered impact areas, HH–EQ–R, respectively [16]. Afterwards, the scores are weighted into a single value (EI‟99). The results of the application of the LCA Model, presented on Fig. 11, show that the life cycle of the FoP, PP, has lower impact on the environment than the RBDPs. Despite of registering relatively high impacts on the materials production stage (reflected on Fig.11 at injection materials), bigger than 10/90 and 40/60, the main reason for the PP to have such smaller environmental impacts has to do with the avoided new material that the recycling of the products in end of life permits and with the smaller energy consumption during the injection process. Among the R-BDPs, 10/90 is the one that registers smaller impacts and 90/10 the most environmentally damaging. The arising impacts from mould production and mould material processing stages are practically negligible on the overall impacts, while the injection moulding stage presents moderate impacts. As expected, plastics processing and injection moulding stages have the strongest environmental impacts, accounting 53% and 42% respectively, of the 10/90 life cycle impacts, being this one the R-BDP where this fraction is smaller. LCA analysis clearly shows the influence that the plastics processing stage has on the final results. Also the

3.4 Functional Assessment In this section the Functional Assessment of the plastics in comparison is presented. The followed methodology of analysis (Fig. 12), considers the most important functions that must be performed by plastics and also its relative importance.

Fig. 12: Functional Assessment methodology

This analysis stands out from the economic and environmental analysis since this analysis is dedicated to the use stage of the plastics‟ life cycle. Hence, for this analysis is required to define a specific group of typical applications for R-BDPs manufactured by injection moulding process. Typical applications for R-BDPs made by injection moulding are usually disposable products for domestic environment utilization. Among several possibilities of that kind of products, it was chosen a group of 4 different products – including 2 packaging products (a food package and a liquid container), 1 catering product (cutlery) and, 1 hygiene product (disposable tooth brush) – from which were identified and selected (on discussion with users and fellow researchers and complemented with 6

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics research) the functions (Tab. 5) that must be performed by the plastics in comparison, enabling to perform the Functional Assessment. Such functions have different levels of importance for the functional performance of the products and this effect was modelled through the attribution of an importance weight. This attribution might not be an easy task, especially if the functions are so unlike. In this case that task relied on the users‟ expectations of performance for the selected products, which was assessed by means of a public survey made directly to users. In this survey, based on pairwise comparisons of functions, the respondents were asked to

Lightness

related to the products‟ weight which will have effect on transportation and handling

Strength

related with the products‟ capacity to resist to impacts and handling and to do not degrade easily

Ecofriendliness

Regarding to the ability to cause less environmental impacts but also as a marketing asset to appeal to buyers

Appearance

related to the visual aspect of the product, which is always important when it comes to choose between similar products

Tab. 5: Selected functions for the FA analysis

Product Functions

Weight [%]

Lightness Strength Eco-friendliness Appearance Sum Weighting (%)

9% 43% 36% 12% 100% -

Maximum Strength [Mpa] 4 10

give a score of importance (0 - as important; 1 – weakly more important; 2 – moderately more important; 3 – strongly more important) to the more important function between a set of two functions, repeating the process to all the 4 selected products. To correlate each function to one or more properties of the candidate materials, a total of 15 points were distributed among the material properties to each function, considering their relevance to the function. Based on the functions‟ weights and on the properties scores, each material property represents its importance to the plastics Functional Assessment. The analysis of Tab. 6 identifies Maximum Strength and Biodegradability as the most important properties for the plastic products performance. Hence, the ability of the R-BDPs to be biodegradable it‟s expected to have a major contribution to the overall functional performance. To complete all the required information to compare the functional performance of the plastics in comparison is only missing to collect the values of each property. The values for Maximum Strength and Young´s Modulus were collected from the flexural tests made to a series of samples. Since the chosen material properties have different units, they had to be adimensionalized in order to be compared. The adimensionalization is done attributing scores in a 10 point scale (1 for the worst material and 10 for the best) to each plastic property value. The evaluation of Biodegradability is based on the plastics‟ content in PLA and STA. From the time biodegradability tests it‟s known that R-BDPs with

Young's Modulus [Mpa] 4 5

Density [kg/m3]

Biodegradability

Appearance

7 15

4.7 31.1%

2.5 16.7%

0.6 4.1%

15 1.8 12.0%

5.4 36.3%

Tab. 6: Weights applied to the material properties

Material properties

Weight [%]

10/90

40/60

80/20

90/10

PP

Maximum Strength

31.1%

Value [Mpa] Adimensional Score

6.17 1 0.3

19.77 5 1.6

34.30 10 3.1

32.21 9 2.8

24.84 7 2.2

Young's Modulus

16.7%

Value [Mpa] Adimensional Score

409.02 1 0.2

1558.81 5 0.8

2559.98 10 1.7

2491.95 9 1.5

1605.54 6 1.0

Density

4.1%

Value [kg/m3] Adimensional Score

1200 5 0.2

1280 2 0.1

1250 4 0.2

1300 1 0.0

905 10 0.4

Biodegradability

36.3%

Value Adimensional Score

10 3.6

7 2.5

4 1.5

4 1.5

1 0.4

Appearance

12.0%

Value Adimensional Score

1 0.1

4 0.5

7 0.8

9 1.1

10 1.2

4.4

5.5

7.2

6.9

5.2

TOTAL SCORE

Tab. 7: Functional Assessment

7

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics higher presence of STA tend to degrade faster, independently of the environment conditions. So the values were attributed according to this variable and are already adimensionalized. As for Appearance, it was evaluated by visual inspection of the injected samples. Finally the adimensionalized value of each material property was multiplied by its importance weight and then the overall result to each plastic was obtained by adding all the properties score. Results from Tab. 7 reveal that the very good mechanical properties and Appearance of the R-BDPs 80/20 and 90/10 significantly contributes to its high scores, being 80/20 the plastic with the highest score. In opposition, despite of 10/90 presenting the best score for Biodegradability, its poorer mechanical properties related functions left it with the lowest final score. Concluding, it can be said that R-BDPs with higher content in PLA have better functional performance and that globally R-BDPs perform better than PP for the functions required to disposable products, exception made for 10/90.

3.5 Global evaluation With the results obtained from the economic, environmental and functional performance dimensions, an integrated and global evaluation can be performed. Once the outcome values from the individual dimensions have different units, they were adimensionalized into a 10 point scale to allow the attribution of importance weights (dimension weights). The adimensional values of each alternative material in Cost, 1, Environment, 2, and Functional, 3, dimensions were calculated by Eq. 1 and Eq. 2 from Tab. 8. The absolute and adimensional values of each alternative material in the three dimensions of analysis are shown in Tab. 9 and to illustrate the existing possibilities regarding each dimension weights, a ternary diagram was used. Each point on the diagram was determined according to Eq. 3 from Tab. 8. The diagram illustrates not only the „„best material‟‟ for a particular set of importance weights but also the domain of weights for each „„best material‟‟. Different combinations of weights might result in a different „„best material for the application‟‟ and a slight modification of such weights might deeply modify this „„best material‟‟. For example, if the strategic goal is the economical aspect, then the scenario required can be represented by point A, where a high weight is given to the economic dimension (90%), a low weight is given to the functional dimension (10%) and a null importance is given to the environmental dimension. For this scenario, the “best material” is PP. On the other hand, if the strategy follows a more balanced

LCC LCA FA

Value [€] Adimens. Value [EI‟99 points] Adimens. Value [points] Adimens.

(

)

Eq. 1

(

Eq. 2

)

(∑

)

Eq. 3

Tab. 8: Formulas for the final results adimensionalization (i – analysis dimension; j – alternative material; aij – adimensional value; Aij – absolute value; wi – dimension weigh with ; P – point coordinate)

concern between economical and environmental aspects, then a good scenario could be characterized by point B, where 40% of importance is given to economic, 50% to environment and 10% to functional performance. This scenario is still under PP‟s domain of “best choice”. Point C illustrates a more extreme strategy oriented towards the functional aspect, with 80% of importance given to functional dimension and the remaining 20% distributed equally between economic and environmental dimensions. For this scenario, the “best material” is now 80/20.

Fig. 13: Global evaluation of the plastics life cycle performance based on cost, environmental and functional criteria. Weight criteria: A – 90% Econ. Perf., 0% Envir. Perf., 10% Func. Perf.; B – 40% Econ. Perf., 50% Envir. Perf., 10% Func. Perf.; C – 10% Econ. Perf., 10% Envir. Perf., 80% Func. Perf.

In this case study and according to the analysis, 80/20 and PP are the only two plastics appearing in the ternary diagram. Therefore, whatever the set of weights chosen those are the materials to consider for the application. The

10/90

40/60

80/20

90/10

PP

76,528 5.6 905.3 8.6 4.4 6.1

73,120 5.9 1350.3 5.8 5.5 7.6

71,407 6.0 1841.6 4.2 7.2 10.0

74,381 5.8 2045.5 3.8 6.9 9.5

42,797 10.0 782.7 10.0 5.2 7.1

Tab. 9: Absolute and adimensional values of the candidate plastics in the dimensions of analysis

8

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics R-BDP 80/20 points out to a strategy associated to the functional performance of the material, while PP points out to a strategy more concerned with economic and environmental costs over the life cycle. As for the other RBDPs analysed goes, they revealed a worst performance than the others regarding the assumptions made in this study, since none of them obtained overall results relatively good enough to exceed 80/20 and PP, whereby they do not “show up” as alternatives in the final decision diagram.

that in the decision domain appears now 2 R-BDPs as “best options". Moreover, R-BDPs have also gained domain space over PP, as PP‟s domain is now much smaller than it was in the initial diagram (Fig. 13) resulting from the main analysis, on which was considered the ideal EOL scenario (S1).

3.5.1 Sensitivity Analysis Since in the initial analysis it was considered the most optimistic EOL scenario (S1) regarding consumers behaviour, the opposite scenario is now considered, the worst case scenario (S4), in which all R-BDPs and PP end up at landfill. The results (Fig. 14), attest the importance of final disposal practices.

Fig. 15: Global evaluation of the plastics life cycle performance considering the EOL scenario of landfill R-BDPs and PP

4. Conclusions Fig. 14:LCA results for EOL scenario of Landfill (S4)

Comparing these with the previous results (Fig. 11) it is possible to see that PP appears now much more environmentally damaging than most of R-BDPs, due to its worse behaviour in landfill. In fact landfilling PP produces almost 3 times more environmental impacts than recycling. As for the R-BDPs goes, the hierarchy on impacts remains the same, though landfilling generating more environmental impacts than composting. Again and as expectable there is a trend of damage increasing with the presence of PLA in the R-BDPs‟ blends. The global evaluation considering, the sensitivity analysis performed, led to some changes (Fig. 15). When changing the final disposal to landfill, 10/90 appears now as an option for moderate economic costs and medium to high environmental concerns. 80/20 is still the best choice whenever the requirements are about high functional performance and the concerns with environmental impacts are reduced. PP remains as the best option when the aim is all about reducing costs. Regarding today‟s society practices in waste management, this EOL scenario option (S4) is more realistic than the EOL scenario chosen for the main analysis (S1), on which it was assumed the best practices of final disposal leading to the preferred EOL waste treatment processes to each plastics‟ type (composting to R-BDPs and recycling to FoPs). However, this EOL scenario option (S4) results in a better global performance of R-BDPs, favouring R-BDPs in the comparison to PP, as the ternary diagram shows (Fig. 15)

This research focused on comparing the performance in plastic injection moulding of Biodegradable and Compostable Plastics based on Renewable Raw Materials (R-BDPs) with different compositions regarding the amount of Starch (STA) and Polylactic acid (PLA). Most studies analyse these materials in terms of environmental impacts, as R-BDP‟s are seen as possible Fossil Origin based Plastics (FoPs) substitutes. However, nowadays decisions are multi-attribute, based also on economical and technical performances. Additionally, a decision based only on price or environmental differential between materials is not enough. In an industrial context, materials are used to manufacture a part or a product and different materials mean different operating conditions or even different processes during production. Moreover, materials may even imply changes in design in order to meet technical requirements. In fact, this study enhances the need to go beyond material properties and to analyse the whole product life cycle. In this thesis four different R-BDP‟s are analysed, differing in the amount of PLA and STA. Whilst STA means lower environmental impacts to produce, PLA performs better during injection moulding, leading to lower cycle time and consequently, higher productivity. The four R-BDPs are also compared to a common FoP, in the case Polypropylene (PP), to evaluate the positioning of these materials relatively to the conventional plastics. Overall results shown that PP outcomes R-BDPs not only in the economic dimension but also in the environmental dimension, in which dimension the R-BDPs were expected to perform better. . In fact, R-BDPs with higher content of 9

Life Cycle Engineering approach to analyse the performance of biodegradable injection moulding plastics STA, blend with 10% PLA and 90% STA (10/90) and blend with 40% PLA and 60% STA (40/60), proved to produce lower impacts than PP on their material processing stage, but the final disposal option of recycling PP, in opposition to composting R-BDPs, and consequently the avoided production of new material that recycling permits, favoured the FoP. Therefore, the importance of life cycle analyses was verified. Nevertheless, the R-BDP material blend with 80% PLA and 20% STA, (80/20), “shows up” in the decision diagram as the best choice when the selection is done concerning functional/technical aspects. Notice that when changing the End of Life (EOL) scenario to the more realistic option of landfill R-BDPs and PP, R-BDPs revealed to be better choices than PP regarding the environmental aspects, as the R-BDP blend with 10% PLA and 90% STA, (10/90), appeared then as the “best material”. The material composed of 80% PLA and 20% STA, (80/20), remained as a good choice in terms of functional requirements and as expected PP maintained the better scores regarding economical strategies; contributing for that, its lower acquisition costs. Finally, the main conclusion is the importance of analysing the whole life cycle of a product. As results show that the substantially higher economical costs of R-BDPs do not always compensate the environmental advantages that they promote, being these directly correlated to waste management practices and ultimately with consumers environmental consciousness.

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