Claudia 29.06.2017 Retusat [303886]

PROIECT DE DIPLOMĂ

Absolvent: [anonimizat]:

Ingineria Designului de Produs

Conducător științific:

conf.dr. Cristina CAZAN

Brașov

2017

CLAUDIA CRISTEA

RECICLAREA MODULELOR PV SUB FORMA DE MATERIALE COMPOZITE CU APLICABILITATE IN DOMENIU CONSTRUCTIILOR

PROIECT DE DIPLOMĂ

Program studii:

Ingineria Designului de Produs (lb. eng.)

Brașov

2017

Abstract

Ever increasing amounts of plastics are being produced and used during the last decade and today. A [anonimizat] a wide range of applications. [anonimizat].

[anonimizat]. Polypropylene (PP), high density polyethylene (HDPE) and polystyrene (PS) were combined in different compositions and the composites were tested to discover if these materials have sufficient properties to be used in construction applications.

[anonimizat], is getting an ever growing problem in the world of today. [anonimizat]. It’s [anonimizat] a big role in the development and creation of new technologies. Decent and realistic solutions need to be found for the problem of the ever growing use of plastics. [anonimizat].

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However, [anonimizat] a material of resource. [anonimizat]. Nowadays a [anonimizat] a waste product. Due to difficulties to conserve the material’s [anonimizat]. For example the mechanical properties of a recycled material are different from those of the corresponding original material.

The goal of this paper and the research done is to find an optimum point where the properties of the recycled material are sufficient enough to be used again as construction materials and thus can be used as if they were original materials. This point was determined by experimentation on different combinations of recycled materials and by varying the ratio of the materials used in the blend.

Plastics

Signification of plastics

“Plastic” is a generic term for numerous materials that differ in structure, properties, and composition. The properties of plastics vary so widely that they are often used to replace conventional materials, such as wood or metal.

Definition of plastics:

Plastics are materials whose essential components consist of macromolecular organic compounds. These compounds are created synthetically or by convention of natural products.[1]

Composition of plastics

The basic substance for polymers are called “monomers” (mono=single, meros= part) (Fig.1). The term “macromolecule” is derived from the large size of these molecules (macro=large). These large molecules results from the combination of many thousands of monomer molecules. (Fig.2)

Fig. 1 Schematic monomer molecule [1]

Fig. 2 Macromolecule (chain elements) [1]

Macromolecules are formed from many identical monomers in the simple case; they consist of a sequence of identical chain elements. Each chain molecules has a continuous line of chain elements.

The basic materials for the monomers are primarily crude oil and natural gas. Because carbon is the only element essential for polymers, it is theoretically possible to create monomers from wood, coal. But these substances are not used because it is inexpensive to produce monomers from gas and oil.

Raw material for plastics

In the production of plastics are natural substances, such as cellulose, coal, petroleum, and natural gas. The molecules of the raw materials have in composition carbon (C) and hydrogen (H). Also in the composition of materials can be involved oxygen (O), nitrogen (N) and sulfur (S). But the most important material for plastics is petroleum. Fig.3

Fig. 3 Properties of the various products made from petroleum as percentages of total production

Properties of polymers

Plastics and natural materials such as rubber or cellulose are composed of very large molecules called polymers. Polymers are constructed from relatively small molecular fragments known as monomers that are joined together.

Wool, cotton, silk, wood and leather are examples of natural polymers that have been known and used since ancient times. This group includes biopolymers such as proteins and carbohydrates that are constituents of all living organisms.

Synthetic polymers, which include the large group known as plastics, came into prominence in the early twentieth century. Chemists' ability to engineer them to yield a desired set of properties (strength, stiffness, density, heat resistance, electrical conductivity) has greatly expanded the many roles they play in the modern industrial economy.

Let's begin by looking at an artificial polymer that is known to everyone in the form of flexible, transparent plastic bags: polyethylene. It is also the simplest polymer, consisting of random-length (but generally very long) chains made up of two-carbon units. Fig. 4

Fig.4 Structure of polyethylene [2]

You will notice some "fuzziness" in the way that the polyethylene structures are represented above, Fig.4. The squiggly lines at the ends of the long structure indicate that the same pattern extends indefinitely. The more compact notation on the right shows the minimal repeating unit enclosed in brackets overprinted with a dash; this means the same thing and is the preferred way of depicting polymer structures.

Classification of polymers

Polymers can be classified in ways that reflect their chemical makeup, or perhaps more importantly, their properties.

Chemistry:

Nature of the monomeric units

Average chain length and molecular weight

Homopolymers (one kind of monomeric unit) or copolymers;

Chain topology: how the monomeric units are connected

Presence or absence of cross-branching

Method of polymerization

Properties:

Density

Thermal properties — can they soften or melt when heated?

Electrical conductivity

Degree of crystallinity

Physical properties such as hardness, strength.

Solubility, permeability to gases

Mechanical properties of polymers

Polymers possess a wide range of mechanical behaviors and can be: strong, weak, fragile, ductile or combinations (fig.5)

Fig. 5 Examples of variation of tension curves – deformation of polymers [3]

The mechanical properties for the composition of a particular polymer strongly depend on the degree of crystallinity and the molecular weight (fig.6).

Fig. 6 Effect of molecular weight and degree of crystallinity in the mechanical behavior of polymers [3]

These properties affect, in particular, the rigidity of the pine chain breaking. The short chains present in the mass of the polymer can act as plasticizers for the molecular weight distribution and facilitate the movement of the chains. They interact with efficient packaging of long chain molecules.

Applications:

molded and formed objects ("plastics")

sheets and films

elastomers (i.e., elastic polymers such as rubber)

adhesives

coatings, paints, inks

fibre and yarns

Physical properties of polymers:

The physical properties of a polymer such as its strength and flexibility depend on:

chain length – in general, the longer the chains the stronger the polymer;

side groups – polar side groups (including those that lead to hydrogen bonding) give stronger attraction between polymer chains, making the polymer stronger;

branching – straight, unbranched chains can pack together more closely than highly branched chains, giving polymers that have higher density, are more crystalline and therefore stronger;

Cross-linking- if polymer chains are linked together extensively by covalent bonds, the polymer is harder and more difficult to melt.

Crystalline and amorphous polymers

In a polymer the molecules are chains containing potentially millions of formula units. There is, however a repeating unit in a polymer – the monomer from which it was made. This must be the basis of both long and short-range order in a polymeric material.

For example, a short section of linear polyethylene it’s represented in fig.7

Fig. 7 Section of linear polyethylene [4]

However, the conformation of the bonds around each carbon atom can be represented schematically as follows in fig.8

Fig. 8 Newman projections [5]

These diagrams are called Newman projections. The circle is a single C-H bond; and this diagram represents a projection along it. These two structures thus represent one half of the backbone continuing on either side of a C-C bond (trans), or both halves on the same side (gauche). Note that there are two possible gauche states, labelled gauche (-) and gauche (+).

Whilst the trans conformation has a lower energy (since it's easier to position the hydrogen atoms on the carbon backbone further apart), an all-trans conformation would be a considerably more ordered structure than a random one – that is, it has a much lower entropy.

Amorphous polymers are generally found in a random coil conformation and have a disordered chain structure fig.9. This is the most common structure of many polymers. Crystalline polymers are predominantly in the all-trans conformation, and the chains are arranged in lamellae, as below:

The polymer crystal is made up from one-dimensional chain-folded sequences, shown on the above left, where the repeat distance is given by the chain spacing. To the above right is shown a schematic arrangement of folded chains into a two-dimensional lamella.

An amorphous polymer has the maximum entropy conformation (given by the Boltzmann distribution), and the chains are arrayed randomly throughout the material, making atomic positions quasi-random as in any other glassy material.

As a result of the difference between the amorphous and crystalline arrangements of polymer chains, the X-ray diffraction patterns of the two phases are very different. The amorphous phase contains no long-range order, meaning that there are no regular crystalline planes to diffract X-rays. Thus the incident X-rays are scattered randomly and there are no sharp peaks in the diffraction pattern. In the crystalline phase, the repeating lamellar chains provide a regular structure, thus the diffraction pattern will contain sharp, prominent signature peaks, the position of which depends on the exact spacing between chains. As the degree of crystallinity of a polymer affects its properties, accurately determining it is important. X-ray diffraction can be used to determine the degree of crystallinity of a sample. Thermal analysis techniques such as differential scanning calorimetry (DSC) can also be used. The two determinations may not necessarily be in agreement, and the reasons for this are complex.[5]

Thermal Properties of Polymers

Thermoplastics:

Plastics consisting of macromolecules with linear or branched chains held together by intermolecular forces are called ‘thermoplastics”. The strength of the intermolecular forces depends on the type and number of branches or side chains, among other facts.

A thermoplastic polymer is a type of plastic that changes properties when heated and cooled. Thermoplastics become soft when heat is applied and have a smooth, hard finish when cooled. There are a wide range of available thermoplastic formulas that have been created for many different applications. To produce composite materials using thermoplastics, high pressures and temperatures are necessary.

Fig. 10 Structure of amorphous and semicrystalline thermoplastics [1]

Thermosets:

Thermosetting resins (in short: thermosets) do not melt on heating, but ultimately disintegrate. From a molecular point of view, most thermosets consist of relatively short chains ensuring the non-cured polymers to have very low viscosity. Curing is carried out by initiating a chemical reaction, in which the short chains form bonds and create a three-dimensional ‘cross-linked’ network. The temperature is often regulated during curing.

Glass transition temperature (Tg)

The glass transition temperature (Tg) is the temperature at which a resin passes from the 'glassy' state (rigid and brittle, i.e. little plastic deformation at fracture) to the 'rubbery' state (slack and tough). It is not recommended to use a composite in the vicinity of or above this temperature. The effect of exceeding the glass transition temperature is much stronger with thermoplastics than with thermosets, but is reduced for both by the reinforcing material. The glass transition temperature depends on the circumstances during curing (for thermosets). A higher glass transition temperature can be achieved by curing at higher temperatures and with longer periods of heating.

Thermal behavior of polymers:

Polymers are characterized by two important temperatures:

The melting temperature – at which the transition between the solid polymer and the liquid occurs.

The glass transition temperature – at which transition occurs between regions where the polymer is relatively rigid (under Tg) and those in which it is relatively similar to rubber / plasticized (over Tg).

This temperature is also affected by the molecular weight of the polymer mass fig.11

Fig. 11 Effect of molecular weight on melting and glass transition temperature [3]

Life cycle of a product

According to the World Commission on Environment and Development (WCED), sustainable development is: "development that meets the needs of the present without compromising the ability of future generations to meet their needs".

From the designer point of view, the significance of the concept of sustainable development is to design products using less resources Fig.12. Sustainable development has 3 components: economic, ecological and social.

Fig. 12 Consumption of renewable resources

A product system goes through a number of consecutive and interlinked stages potentially ecologically dangerous Fig.13. These stages are called "Life-cycle of a Product" because a product has a life that starts from "raw material acquisition or generation of natural resources, over manufacture, transport, and use to the final disposal

Fig. 13 Life cycle of a product

A product has a life that starts with the raw materials extraction, passes through the manufacturing process and assembly, the purchase of the complete product (including transportation, packaging, advertising etc.), the use or consumption and the end-of-life. Finally the product can be ‘reborn’ by reuse or recycling the materials and so the circle is closed forming the so called Life Cycle.

All the stages of the product Life-Cycle are potentially dangerous for the environment. LCA is the abbreviation for the Life-Cycle Assessment which represents the evaluation of the environmental impact during all stages of the Life Cycle of a product.

The materials used for eco-products:

Should come from renewable/sustainable sources;

Their environmental impact during extraction, transportation and processing should be reduced;

Must not be hazardous for humans and environment (both as a product or waste);

Must permit recycling.

A clean technology /process responds to human needs (connecting it with sustainable design):

Avoids waste (efficient use of materials);

Minimises emissions;

Ensures an efficient use of energy.

Recycling

Meaning of recycling:

Recycling means the process of converting waste materials into new materials and objects in order to save materials and help lower greenhouse gas emission. By recycling we can prevent the waste of potentially useful materials and reduce the consumption of fresh raw materials, thereby reducing the energy usage, air and water pollution.

WASTE MANAGEMENT

In Romania, the Ministry of Environment and Forests promoted public interest documents, such as eco-guide public official Eco-tourist guide and guide eco-citizen, containing recommendations on:

Energy consumption reduction and energy waste and waste material avoidance, applied to both institutions and citizens;

Separate collection of all types of waste, especially Waste Electrical and Electronic;

Limiting environmental pollution through voluntary actions for waste management, reducing resource consumption, using biodegradable materials, the practice of responsible eco-tourism activities as against nature;

Basic principles of environmental policy in Romania are set in accordance with European and international provisions, ensuring protection and nature conservation, biological diversity and sustainable use of its components.

Currently, the waste hierarchy shall apply as a priority order, in four steps to according Directive 2006/12/CEE, but by the end of 2010, following the transposition of the new waste directive 2008/98/CEE there will be applied the five-step waste hierarchy: prevention, preparation for reuse, recycling, other recovery and disposal operations.

According to the legislation in force, the waste producers have the responsibility management of waste including waste prevention, recycling, and disposal. In 2007, over 419,000 tones of hazardous waste were generated; representing a 0.15 % of total of generated waste Tab.1. Most of this hazardous waste was co-incineration or incineration in the producer own facilities or private operators’ facilities, or landfilled. [6]

In the Tab. 1, 2, 3 and the Fig.14, 15, 16 are represented the total waste management in Romania for a period of 5 years (2003-2007)

Table 1 Management of hazardous industrial waste, 2003-2007 [6]

Fig. 14 Management of hazardous industrial waste, 2003-2007 [6]

Table 2 Management of non-hazardous industrial waste, 2003-2007 [6]

Fig. 15 Management of non-hazardous industrial waste, 2003-2007 [6]

Table 3 Management of municipal waste, 2003-2007 [6]

Fig.16 Management of municipal waste, 2003-2007[6]

Recycling of materials

As mentioned before, plastics are normally not biodegradable, due to the nature of their chemical structure. Therefore it is very important for our environment to try to reduce the amount of plastic waste. One way of trying to reduce this waste stream is by recycling the used materials into useful products again. Not only for the environment impact, but also on a financial level, recycling is a very interesting and promising process. [4]

However, recycling of plastics is often a more challenging process than the recycling of lucrative materials such as metal, this due to their low density and low value. The main difficulty of recycling plastics is the problem of dissolving the long macromolecular chains. For plastics to be reused and mixed in new materials the recycled materials should be identical to allow efficient mixing. When different types of plastics are melted together, they tend to phase-separate and set in layers. At the boundaries of these phase separations the material will have its structural weakest point, and as a result the material will break at these points first. So these recycled materials are only useful in certain applications.

Another mayor difficulty regarding recycling plastics is the widespread use of dyes, fillers and different kind of additives blended in the plastic materials. In general polymers are too viscous to remove the fillers in an economical interesting way, and cheaper processes of removing the additives ore dyes tend to damage the polymer.

A third difficulty to overcome when recycling is the fact that many small plastic products or bags don’t have the universal sign displaying the material the product is made of. (An overview of the different kind of symbols used to categorise the different kind of plastics can be seen in Table 4.)

The resin number is contained in a triangle Fig.17.

Table 4 Resin identification code [2]

*society of the plastic industry

Fig. 17 Plastic symbols with resin identification cod [7]

The process of recycling begins with the separation of the different kind of plastics according to their resin type. The resin identification code (RIC) (as seen in the Figure above) was formerly used as a method of categorising the different types of polymers. This identification code was developed by the Society of the Plastics Industry in 1988. Nowadays most plastic recycling companies use an automatic system to sort out the different kinds of plastics, an example of a system like this is near infrared technology (NIR). Also the colour of the plastics plays a big role in the separation before recycling. [5]

After separation of the different plastic materials the plastics are shredded. The shredded particles then are filtered to remove impurities like paper labels. After this step, the fragments are melted and extruded into pellets which are then sold to producers of plastic products to manufacture a new product with the recycled material. In Figure 10 the relationship of the recycled amount of different materials can be seen. It can be noticed that PE is the most recycled polymer [13].

Fig. 18 Percentage of materials recycled

Recycling polyethylene and polypropylene

In the last decade, a rapid increase of the production and use of plastics can be notified clearly. When one compares the quantities of plastics produced in the world in the last 100 years, a significant increase can be seen.

In the 1930’s, approximately 100,000 tons of plastics, excluding rubber, were produced. This quantity reached around 25 million tons in 1976. Due to the development of new technology’s, the production of the plastics reached 90 million tons in 1990. Fifteen years later, in the year 2005, this number exceeded 500 million tons [6].

Every year, millions of tons of plastics are produced in the world, furthermore many different kinds of plastics are produced. When we observe all the different plastics that are manufactured in the world, we can see they exist in the following percentages: 31% polyethylene (PE), 17% polyvinyl chloride (PVC), 15% thermosets, 14% polypropylene (PP), and 9% polystyrene (PS). In addition, other kinds of plastics not mentioned here make up about 14% of the world production. Thermoplastics constitute 85% of consumed plastics [7].

Because of the reason that plastics are so massively used throughout the word, recycling these materials and using these recycled materials is becoming of ever increasing importance. Naturally it is clearly very important to produce and consume plastic materials in an environmentally friendly way.

Because of the fact that plastics are built completely out of organic compounds, it takes a very long time for the material to degrade. Making their process of decay their main disadvantage. Making use of waste plastics is an important element in the economy of all countries, doing this, the used material can re-enter the production chain as a resource and therefore regain again an economical value.

The main steps in recycling plastics from used material to a reusable source are as followed:

collecting plastics from solid wastes

compaction and concentration of the collected wastes

processing concentrated waste plastics according to categorisation

Separating the plastic materials from other solid waste in a healthy manner is the key to recycling them. The preferred method is categorising solid waste at their source, the point of collection, in that way it’s easier for each material to be treated accordingly to the best way for the material to be recycled.

The ratio of volume to weight of plastics is high. This creates important problems in separating, collecting, and evaluating these wastes effectively and economically. The plastics best suited for recycling are PE, PP, PVC, and polyethylene terephthalate (PET). The main objective of separating plastics from the collected solid waste is that the recycled plastics are as pure as possible. [8]

The costs associated with recycling PE and PP plastics in Europe are given in Table 1. As can be seen from these values, the cost of recycled plastic is low when compared with the cost of first production plastic (also called virgin plastic). Recycling and using recycled materials is of great importance to the economies and development of countries, because of this fact.

Table 5 Costs associated with recycling

Recycling can be performed throughout many different technologies. The critical point in recycling plastic materials is using a method which least effects the chemical structure of the plastics, so the properties of the plastic can remain the same after recycling.

The methods and their rates of recycling are different for every kind of plastic (see Table 2). It is expected that the annual consumption of the recycled plastics will increase almost 4% each year. In contrast, the annual consumption of virgin plastics in Europe is expected to increase 3% per year. This means that in the year 2005, almost 60% of the plastics in Europe were recycled. However, these recycled plastics have not yet proved themselves to be a continuous and reliable source of raw materials of quality. [8]

Table 6 Recycling ratio of plastics

It is impossible to achieve the same mechanical properties for a mixture of virgin material and recycled material, when compared to the mechanical properties of the virgin material. However, it is possible to find an optimum point. These optimum points can be determined by means of experiments.

In the research of C. Meran et al. the polyethylene and polypropylene with low and high-density were recycled and mixed with original materials in various proportions, and then their mechanical features were examined. The mixtures were prepared in samples of 5 kg, and then were made ready for injection. The test bars were prepared in moulds. Tensile experiments were carried out with these moulded bars. During the experiments, three of the test bars of each different mixture were broken and the average results were obtained. (See Table 7.)

Table 7 Technical properties of LDPE, HDPE and PP

The results of the tensile test samples, which were obtained for the various mixture proportions for LDPE, HDPE and PP, and the values of the elongation before rupture, are given in Figures 19 and 20. In these figures it can be seen easily that for these three types of plastics, the tensile strength values and the percent elongation values decrease linearly as the percentage of the recycled material mixed with the pure material increases.

Fig 19 Ultimate tensile strength values of LDPE, HDPE and PP

Fig 20 Percent elongation values of LDPE, HDPE and PP

The experiments done by C. Meran et al. demonstrate that the material which can be most successfully recycled and reused is polypropylene. Its tensile strength, even in bars pressed from the highly recycled polypropylene, decreased 15% compared with the virgin material. The polypropylene is followed by the high-density polyethylene with a 24% decrease and by the low-density polyethylene with a 36% decrease.

As can be seen in Figure 20, the elongation of bars pressed from recycled low-density polypropylene is decreased 28% when compared to the elongation of the pure material. The low-density polypropylene is followed by the polyethylene with a decrease of 35% and by the high-density polyethylene with a decrease of 40%. [8]

To conclude the research of C. Meran et al., it can be said that in the tensile experiments carried out on the high- and low-density polyethylene and the polypropylene, that the tensile strength values and the values for the percent elongation decreased linearly as the percentage of the recycled material mixed with the pure material increased. Hereby concluding that that the mechanical properties of the material also weaken.

Recycling of post-consumer HDPE

A. Boldizar et al. did research on the behaviour of high density polyethylene that was recycled after consumer use. The HDPE came from used plastic bottles. The goal of the research was to find out the effects of adding a commercial re-stabilizer to the recycled material, and to discover the changes it has on the mechanical and chemical properties of the recycled HDPE, and especially the resistance against ageing.

Recycling plastics materials is increasing since the last few decades, however, for the recycled material to be of practical use, it’s important that the mechanical properties of the material must be contained, so further use of the material is possible. So to discover the effects of adding different stabilizers to the material and figure out which additive contains sufficiently the properties of the material, A. Boldizar et al created a simulation procedure which re-enacts the process of multiple cycles of use and recycling.

The method of experimentation was based on conventional extrusion and accelerated thermos-oxidative ageing, whereby the cycle of production and recycling was preformed 10 times. The extruded film was 0.4mm thick, and it was thermo-oxidized to accelerate the ageing process. The ageing process took place for 48 hours at a temperature of 110°C, corresponding to a two to three years of indoor use.

After the extrusion of the material, the extruded film was cut into pieces and recycled, while adding a re-stabilizer to contain the properties of the material. The re-stabilizer used was Recyclostab 411, which consist of phenolic antioxidants, co-stabilizers and phosphite, after each extrusion cycle a 0.1 wt% of Recyclostab 411 was added.

At the end of the 10 cycles of extrusion and ageing, elongation at break, melt flow rate (MFR), were measured to discover the degradation of the mechanical properties. To discover the change in chemical properties, size exclusion chromatograph (SEC) was used.

During their research A. Boldizar et al. discovered that after the 10 cycles of extrusion and recycling, the investigated HDPE material did not show any significant sings of degradation.
All the results of the experiments done on the material stayed within the maximal range of errors for the measurements. (See Table 8.)

Table 8 Properties of HDPE

Because of the fact that HDPE has only a small amorphous fraction, the material was able to withstand the process of the thermo-oxidation for a long period of time. Which are promising results, because this means that the combination of HDPE together with the additive Recyclostab have good properties to be used for long term recycling. [9]

Influence of recycled material in HDPE injection moulding

As mentioned above, recycling used plastics is becoming increasingly more important, both for environmental and economic reasons. Especially in the field of injection moulding, due to the ever increasing amount of products produced in that manner. There are two subdivisions to make regarding recyclable plastic materials. The first group consists of plastic parts that are recycled after their lifecycle has ended. The other group consists of scrap parts that don’t make it as a final product to be sold on the market, e.g. leftovers, product waste, failed parts.

For recycling of the second group, mechanical recycling is used. This is the process whereby the scrap parts are ground into smaller pieces that can be reused in the injection moulding machine to make new parts. However due to the granulation process, the recycled materials are of inferior quality than the virgin ones. Inferior quality means that the material has lower mechanical and aesthetic properties, and that the recycled material can behave different during the injection moulding process. Because of this reason, larger companies only allow a certain maximal amount of recycled material combined with raw material. C. Javierre et al. analysed the influence of the percentage of recycled material in a mixture with raw material to obtain the highest fraction of recycled material possible, while still containing the proper rheological behaviour to ensure good injection moulding. (And in specific conserving the process parameters such as injection pressure and clamping force.)

HDPE was chosen to be used as the preferred material to do the experiments on. This because of the fact that HDPE is widely used for a large range of products, so a lot of recyclable material is generated. Also because of the fact that the volume of the products made out of this material is usually very high, so a lot of scrap parts are generated during the changing of the mould, changing of the colour, so a large recyclable fraction becomes available.

The influence of the percentage of the recycled material combined with the raw HDPE is investigated by means of the capillary rheometer. The different blends of recycled HDPE introduced to the raw HDPE are 20%, 40%, 60%, 80% and 100%. After the injection moulding the results are analysed paying special attention to filling pattern, maximum injection pressure and clamping force during filling.

Based on the capillary rheometer tests, C. Javierre et al. compared the viscosity values for three different temperatures (210°C, 230°C and 250°C) and shear rates varying from 80 to 3500 l/s. Due to the constant test temperatures and constant shear rate, viscosity values for the different percentages of recycled material can be evaluated. (See table 9-13.)

Table 9 Viscosity values for T = 210°C

Table 10 Viscosity values for T = 23°C

Table 11 Viscosity values for T = 250°C

Analysing this data, C. Javierre et al. concluded that the higher the fraction of recycled material in the mixture is, the higher the viscosity values are. This increase of viscosity is almost uniform according to the variation of the recycled material percentage.

Injection pressure and clamping force are the most important results of the research of C. Javierre et al., because these parameters are directly influenced by the viscosity of the used material. The size of the machine used and the technical viability of the process is also directly related by clamping force and injection pressure and are thus determined by the viscosity of the material used. Through simulation with the Finite Elements Method (FEM) these parameters are obtained for different values of viscosity. The results of the necessary injection pressure can be seen in Table 8. The results for the necessary clamping force can be seen in Table 9. Injection pressure and clamping forces were evaluated at 98% of filling, in order to avoid overpacking problems and extreme pressure values at the end of filling.

Table 12 Results for injection pressure

Table 13 Results for clamping force

Comparison between the injection pressure and clamping force can be easily established form both tables for the different percentages of recycled materials. Regarding injection pressure, the higher the percentage of recycled material introduced, the higher the increase of pressure is. For raw material the injection pressure needed is 110.6MPa and for 100% of recycled material the necessary pressure is 126.2 MPa, which is around 12.36% higher. This increase is interestedly enough a very similar value to the increase of the viscosity, which is around an increase of 10%. A similar trend reveals itself for the clamping force. Between the raw material and fully recycled material there is a difference of about 996 tons. So the clamping force increases about 12.77%, which is again very similar to the increase of 10% of the viscosity. An important remark to make is that clamping forces are not only affected by viscosity, but also by part geometry and pressure distribution. [10]

What can recycled material become:

HDPE: using raw resources we can save landfill space, energy, water, resources, and reduces pollution. Some of the products that can be made from recycling HDPE (Fig.18):

Crates

Film plastic and sheeting

Floor tiles

Gardening tools, flower pots, and hardscape materials

Non-food bottles – shampoo, conditioner, cleaning products, laundry cleaners, motor oil, antifreeze

Pipe

Plastic lumber – used for playgrounds, outdoor patios, picnic tables, etc.

Recycling bins[4]

Fig. 18 HDPE transformation after recycling [8]

PP: Some of the products that can be made from recycling PP plastic:

Auto parts – battery cases, signal lights, battery cables

Bike racks

Brooms and brushes

Film sheeting

Garden rakes

Ice scrapers

Plastic trays

Shipping containers and pallets

Storage bins

PS: Some of the products that can be made from recycling PS plastic:

Casings for electronics – cameras, video cassettes

Desk trays

Foodservice items – foamed egg cartons

License plate frames

Light switch plates

Packaging material – expandable polystyrene foam (EPS)

Plastic mouldings – architectural

Rulers

Thermal insulation

Thermometers

Vents

Properties of the chosen materials:

In this table will find further information about the chosen materials (HDPE, PP, PS) Tab.5.

Table 5 Properties of chosen materials

After recycling process this materials HDPE, PP, PS will be the main components for the composite materials.

Composite materials

3.1 Signification of composite materials:

A composite material is a combination of two or more materials of the same type or different from a physical and chemical point of view. The two materials work together to give the composite unique properties.

Composite materials have been designed to replace, in a growing proportion, traditional ferrous and non-ferrous materials.

Attempts to achieve new super-performance materials have led to the development of a class known as commodities called Composite Materials. By definition, the concept of "composite" is attributed to a complex system, made up of several materials of a different nature. In this category comes a very large class of products. This is due to the fact that the possibilities of changing the fundamental components, of the "assembly" and manufacturing techniques, the level of performance and cost are practically infinite.

From a technical point of view, the notion of composite materials refers to materials possessing the following properties:

Are artificially created by combining different components

Is a combination of at least two chemically distinct materials

Presents properties that no separate components can have

Advantages and disadvantages:

In addition, it is necessary to know both the advantages and disadvantages of a material. The table below resumes a number of these possible pros and cons. Tab.6

Table 6 Advantages and disadvantages of composite materials

In the above table are mentioned general advantages and disadvantages, but we have to make distinction in the design process because some characteristics are not applicable or they aren’t incompatible in some case. Changes could appear in the weight of the product. Furthermore, costs and sustainability of a design should always be considered throughout the life cycle. The costs of components or life-cycle phases can soar (e.g. investments in a mould) or materials may not be sustainable. [9]

The number of advantages and disadvantages don’t have a powerful impact on the perception of man, the biggest defining impact for the humans is given by the design of the object that can be a grate, success or not.

3.2 Structure of composite materials, classification:

A composite, in the present context, is a multiphase material that is artificially made, as opposed to one that occurs or forms naturally. In addition, the constituent phases must be chemically dissimilar and separated by a distinct interface. Thus, most metallic alloys and many ceramics do not fit this definition because their multiple phases are formed as a consequence of natural phenomena

The main advantages of composite materials are their high strength and stiffness, combined with low density, when compared with bulk materials. In the general case the constituents are reinforcement and a matrix.

One simple scheme for the classification of composite materials is shown in Fig.19, which consists of three main divisions: particle-reinforced, fiber-reinforced, and structural composites; also, at least two subdivisions exist for each.

Fig. 19 Classification of composite materials

3.3 properties of composite materials

The reinforcing phase provides the strength and stiffness. In most cases, the reinforcement is harder, stronger, and stiffer than the matrix. The reinforcement is usually:

Particulate: They may be spherical, platelets, or any other regular or irregular geometry. Particulate composites tend to be much weaker and less stiff than continuous fiber composites, but they are usually much less expensive. fig.20

Fiber: A fiber has a length that is much greater than its diameter. The length-to-diameter (l/d) ratio is known as the aspect ratio. As a general rule, the smaller the diameter of the fiber, the higher its strength, but often the cost increases as the diameter becomes smaller. Continuous-fiber composites are often made into laminates by stacking single sheets of continuous fibers in different orientations. Typical fibers include glass, aramid, and carbon, which may be continuous or discontinuous. fig. 20

Fig. 20 Typical types of fiber [9]

Matrix Phase: The continuous phase is the matrix, which is a polymer, metal, or ceramic. Polymers have low strength and stiffness, metals have intermediate strength and stiffness but high ductility, and ceramics have high strength and stiffness but are brittle.

In polymer and metal matrix composites that form a strong bond between the fiber and the matrix, the matrix transmits loads from the matrix to the fibers through shear loading at the interface. In ceramic matrix composites, the objective is often to increase the toughness rather than the strength and stiffness; therefore, a low interfacial strength bond is desirable.

Both the reinforcement type and the matrix affect processing. The major processing routes for polymer matrix composites are shown in Fig. 21

Two types of polymer matrices are shown: thermosets and thermoplastics.

A thermoset resin sets up and cures during processing, it cannot be reprocessed by reheating. By comparison, a thermoplastic can be reheated above its melting temperature for additional processing.

In general, because metal and ceramic matrix composites require very high temperatures and sometimes high pressures for processing, they are normally much more expensive than polymer matrix composites.

Laminates: When there is a single ply or a lay-up in which all of the layers or plies are stacked in the same orientation, the lay-up is called a lamina. When the plies are stacked at various angles, the lay-up is called a laminate. Unidirectional (0°) laminae are extremely strong and stiff in the 0° direction. However, they are very weak in the 90° direction because the load must be carried by the much weaker polymeric matrix. Plies in the 0°, +45°, –45°, and 90° degrees directions is called a quasi-isotropic laminate, because it carries equal loads in all four directions. Fig.21

Fig. 21 Structures of laminates composites [9]

Composites versus Metals:

The physical characteristics of composites and metals are significantly different.

Therefore, because the fatigue threshold of composites is a high percentage of their static or damaged residual strength, they are usually not fatigue critical. In metal structures, fatigue is typically a critical design consideration. Fig.22

Fig. 22 Stress – strain curves for Al and carbon/epoxy [9]

Process of obtaining composite materials:

Extrusion

Injection molding

Thermoforming

The chosen process for this study is injection molding.

3.4 Injection Molding

Injection molding is the most important process for the manufacturing of molded parts from plastic, about 60% of all plastics processing machines are injection molding types. Injection molding it’s one of the primary processing methods. With this machine we have the possibility to manufacture molded parts weighing from a few mg to 90 kg. The injection molding process it’s represented schematically below. Fig. 23

Fig. 23 Injection molding process [1]

Most plastics processed by injection molding are thermoplastics, but thermosets and elastomers can also be injection molded

Injection molding machine

Most injection machine (fig.24) are general purpose machines. The tasks they perform include the batch manufacture of molded parts

1 injection molding machine; 2 machine base; 3 clamping unit; 4 mold; 5 injection unit; 6 controller

Fig. 24 Components of an injection molding machine [10]

Clamping unit:

The clamping unit with mold mounting platens accommodates the mold.

Injection unit:

The injection unit consists of a feed hopper, cylinder, screw, nozzle, heater bands and servo-electric or hydraulic drives and serves the purpose of melting the molding compound and injecting it into the mold.

Machine base with hydraulic system:

The machine base supports the clamping and injection units.

Components of an injection molding machine

Clamping unit: The clamping unit (fig.25) contains the mold and carries out the following operations:

mold closing

clamping force build-up and locking of the clamping unit

absorption of the locking force

mold opening

part ejection

Clamping unit with direct hydraulic system

Here the clamping force is built up by elastic deformation of the clamping unit (including mold).

With hydraulic force-fit systems, the clamping force is applied directly by hydraulic force

Fig. 25 Clamping unit [10]

Clamping force:

The clamping force is the total of all forces acting on the tie-bars of the clamping unit under strain when the mold is closed (before injection).

The clamping force is also the force which presses the two mold halves together.

Locking force:

The locking force is the total of all forces acting on the tie-bars of the clamping unit when the part is being molded.

The locking force required during injection depends on:

The max. lifting force inside the mold (counter force inside the cavity as the melt flows inside)

The type of clamping system,

The rigidity of the clamping unit and mold.

Injection unit:

The injection unit plasticized the molding compound and injects it into the mold.

Generally speaking, injection units can be equipped with different sized plasticising cylinders, with different screw diameters (fig.26). The larger the cylinder the greater the attainable weight of the molded part, but the smaller the maximum injection pressure.

Screw (piston)-type injection unit

Fig. 26 Screw type injection unit [10]

During the injection process, the screw acts as a piston, which is pushed forward by the hydraulic pressure in the stroke cylinder and presses the material presently facing it through the Nozzle tip in the mold until it is filled volumetrically (injection phase) and the melt is compressed (compression phase).

In the plasticization process the material is supplied in granular form, filled into the feed hopper of the injection unit. From here it goes into the cylinder inside which a screw rotates. The rotating screw plasticizes the material with the aid of the active cylinder heater bands and in doing so, conveys it forwards to the space at the front of the screw. Fig.27

Fig. 27 Injection unit [10]

Applications of composite materials

Composite materials have a large domain of utilization:

Auto industry

Aircraft industry (fig.28)

Bridge structure

Doors and door frames (fig.29)

Medical industry (fig. 30)

Purpose and objectives of the paper

The theme of the paper “Green homes obtained based on „all waste composite” for mountain huts or shelters" is a research theme in the field of recycling of plastic wastes, this being the basis of the concept of sustainable development.

The subject of the paper is to obtain composite materials based on waste materials that will be used to obtain new products.

Objectives pursued within the project:

to carry out a study on plastics recycling

to carry out a study on composite materials, especially those based on recycled plastics

testing and analyzing these composites to observe the properties and behavior of the new material

to obtain the recycled plastics composites (PP, HDPE, PS) through the injection process

design and sizing of the final product and necessary assemblies

establishment of technological flow and installation scheme

Technological flow

A technological flow represents a succession of technological operations through which raw materials, materials, semi-products, subassemblies, etc. pass through in the process of manufacturing a product or executing a work.

Description of unit operations

The description of the unit operations shall be carried out in the order of the projected technological flow of plastics processing, the technological flow is organized according to a logical scheme of raw materials and auxiliary materials, from the collection of plastic bottles to obtaining the finished product.

Processing of plastics

Waste collection involves the collection, processing and transport of waste for recycling. Collecting can be:

Primary – collecting residues in small containers at the place of production;

Secondary – the collection of waste in containers (bins) located in the yard or on the streets

Proper – the collection of waste from secondary collection points and their transport to storage, or recycling platforms, depending on the situation and waste.

Separation:

can be done manually using mechanical techniques in dry (airflow, magnetic separation) or wet (flotation).At this stage on the conveyor belt the impurities such as labels, plugs are removed manually

Rough cutting:

This coarse cutting step is designed to reduce the size of plastic waste for the purpose of transporting or feeding the next steps.

Washing:

It is a washing operation using warm water and detergent. The warm water and the detergent are used to remove paper, paper glue from HDPE bottles. Washing is done in a vertical, cylindrical water bath with a paddle shaker.

Drying

After washing, 70% of the wash solution remains mechanically entrained on the surface of the washed material. Removing it can be done by free, mechanical or air drying.

The centrifugal drier consists of a truncated sieve, two blades fixed on the conical body inside it. Drying occurs due to the rotation movement of a site and a body inside it because the water is mechanically entrained on the surface of the material and thrown towards the wall of the site. Drying is accentuated by the hot air produced by the pallets mounted on the conical body.

Fine grinding

Milling is a mandatory step in the technological process of plastic waste processing and is the operation of diminishing the dimensions of solid materials. Grinding is carried out in mills with knives and a site with a holes diameter of 2-4 mm, thus obtaining granules of material of about 4 mm

Mixing

Mixing is a stage of preparation of the processing process, this ensures the uniform distribution of the ingredients. Mixing is a complex process influenced by the characteristics of the materials (nature, density, granulation, coefficient of friction), the characteristics of the equipment used to mix the materials and its operating parameters. This operation is performed with the mixer that calculates the required volume of a batch.

.

Injection

The injection of plastic materials is carried out by means of a horizontal injection machine which is characterized by the existence of two basic units: the injection unit of the feeder device, the thermoplastics equipment and the injection and closing system comprising the system Injection molding closing and opening of a mold, injection molding device and protective system.

The injection machine can operate with a manual, semi-automatic or automatic cycle. The manual is used to adjust the machine, the semiautomatic cycle is used when the working parameters have to be changed, and the automatic cycle works after a predetermined program.

Debugging

Debugging is the operation of removing the excess material from the finished product obtained by injection. This operation can be done manually on a conveyor belt or more modern, automatically with the deburring machine.

Packaging

Is the technology of enclosing or protecting products for distribution, storage, sale or use. Packaging can be described as a coordinated system of preparing goods for transport, warehousing, logistics, sale, and end use.

Scheme of the installation

The scheme of the installation it’s based on the technological flow process

Fig. 31 Scheme of the installation

Design and sizing

The 3D design of the house was made in the 3D modeling software called Catia V5R19.

The modeling software made possible to design a multiple variation of forms. All these forms can be used to obtain a modular house.

The main step is to obtain modules that make possible the construction of the house in an easy way.

It will be used modular elements, making possible an easier mounting process.

The future house will look like in figure below.

Fig. 32The 3D model made in the Catia program

The rooms will be placed in a cross shape, to make that possible the main room will have symmetrical octagonal shape.

The height of each room will be of 3 meters and the width of 3 meters. The roof of the room is a dome shaped one. (Figure. 32)

Fig. 33 The section view of the room wall

For each room takes three modules of 1-meter length showed in the following picture fig. 34.

Fig. 34 Module used for the walls.

The walls are made of two layers. First layer represents the interior of the house. (Fig.33)

Fig.35 The interior side of the first module

The firs layer has a thickness of 15 cm. In order to obtain a good isolation, between the two layers is a gap of 10 cm. (Fig.36)

Fig. 36 The gap between the two elements.

Second layer will have contact with the first one and with the exterior. Both modules have similar construction, on the first layer to make a gap between the two modules it is used spacers with a width of 10 cm. On the second layers’ same spacers can be found but in this case it will be used to hold the soul used to cover the house making this way eco-friendlier.

The main octagonal body will be made by using two types of modules.

The first type has the following shape showed in fig.37

Fig. 37 The 3D shape of the beam

It will be mounted into the ground and represents the corners of the house.

Fig. 38 The beam used to obtain the form of the house

Dimensions of the beam is represented in the following figure

Fig.39 The beam main dimensions

The total length of the module is 3.6 meters. The second module is a cross beam used to construct the walls. (fig.40)

Fig. 40 The beam used to construct the wall

Each module has a length of 4 meters and width of 40 cm. To make possible a stabile connection the bodies will have the form showed in fig. 41

Fig.41 The form of the beam

One side will have a groove to increase the stabile connection between the two elements.

The entrance will be mounted one of the sides, the other three will be used for rooms.

To reach more sunlight in the rooms, on each room side will be mounted semi lucid glass.

On the main body will be mounted one roof made from glass in order to increase the interior light. All these elements mounted together results the assembly showed in the figure below.Fig . Fig.42 The real 3D model

Experimental part

7.1 Working method

The specimens were obtained in the laboratory of the Transilvania University Research Institute, using the injection machine. These were made of granules of High-density Polyethylene Recycled, Polypropylene Recycled and Polystyrene Recycled.

For the experimental testing of the composite material, the percentage for the materials are HDPE-50%, PP-25% and PS-25%. After the manual mixing of the composition, the injection machine needs to be prepared. Fig 30

Fig. 43 The interface of the injection machine

In the plastification process the material is supplied in granular form, filled into the feed hopper of the injection unit. From here it goes into the cylinder inside which a screw rotates. The rotating screw plasticises the material with the aid of the active cylinder heater bands. After this step the specimens is automatically released from the mold.

After the injection molding process, by varying the working parameters (tab. 7) have resulted 11 specimens of type HDPE: PP: PS=50:25:25 %, with a quantity of 1.5 kg of granular recycled materials (750g HDPE, 375g PP, 375g PS).

Tab. 7 Parameters of the 11 specimens

In the Tab.7 are represented the variation of working parameters for the 11 specimens.

Signification of the arrows:

The red arrow represents the lower values for the different types of parameters

The yellow arrow represents the medium values for the different types of parameters

The green arrow represents the high values for the different types of parameters

The injection temperature of plastics (HDPE, PP and PS) is in the range between 200 – 270 degrees Celsius.

Specimen testing

The specimens were tested on the following machines:

Traction machine – compression (Z020, Zwich/Roell)

Impact test equipment

Traction machine – compression:

The specimens were subjected to mechanical tests on the traction and compression machine (Z020, Zwich / Roell).

The principle of the traction test method is to stretch the specimen along its main axis until it breaks or until the deformation reaches a predetermined value. The supported load (force) and elongation of the specimen are recorded.

The traction device is composed of two jaws, an actuator jaw and a clamping jaw, between the two jaws being attached to the specimen.

The shape and size of the specimen is determined by the nature of the material from which it is made. In the case of composite materials based on HDPE, PP and PS recycled, the dumbbell shape specimen is used, the elongation or rupture takes place in the center zone, the narrower zone.

The principle of the compression test method consists in compressing the specimen along its main axis to breakage or until tension or deformation (compression) reaches a predetermined value. Recorded load and compression of specimen are recorded.

Impact test equipment

The principle of this method consists in positioning the horizontal specimen on the two strings and subjected to a shock test by a single hit. The specimen is fixed at one end, the other being free, this free part will be hit by the pendulum hammer. This method determines the impact energy absorbed by the sample up to the moment of rupture.

The impact test is used to determine the behavior of materials at high deformation rates. With this appliance, it is possible to test plastic, ceramic and composite impact.

References:

[1] W. Michaeli, L. Walters, H. Greif, F.J. Vosseburger, Plastics Technology

[2] http://www.chem1.com/acad/webtext/states/index.html [18:22 / 10.01.2017]

[3] Donald R. Askeland – Pradeep P. Phulé. The Science and Engineering of Materials, 4th ed. Brooks/Cole. Ch.15 – Polymers. 2003

[4]https://www.bing.com/images/search?view=detailV2&ccid=qVgK1mlO&id=0B920BE1DC66F656E9D1485767D1A49A76C68EA5&thid=OIP.qVgK1mlOmVQj84qIto2AeQEsA8&q=short+section+of+linear+poly(ethylene)&simid=608030133567751889&selectedIndex=19&ajaxhist=0 [13:08 / 12.01.2017]

[5] https://www.doitpoms.ac.uk/ [19:58 / 12.01.2017]

[6] https://sustainabledevelopment.un.org/ [16:21 / 29.01.2017]

[7]https://www.bing.com/images/search?view=detailV2&ccid=2by5ZTJF&id=55CCC7583C876E0271643DCA8BB12E125B849570&thid=OIP.2by5ZTJF31lsMc1rPJr_jgEsCE&q=coduri+reciclare+plastic&simid=608051389343467103&selectedIndex=2&ajaxhist=0 [20:07 / 23.02.2017]

[8]https://www.bing.com/images/search?view=detailV2&ccid=0UBSAn53&id=F8D2D27E9234F80CE98B5359D07B38B22F7E38B3&thid=OIP.0UBSAn53qzAwDTL-WvSwdQEsC1&q=products+made+from+recycled+plastic+%232&simid=608005171259900762&selectedIndex=0

[9] R. P. L. Nijssen, Composite Materials. An Introduction

[10] https://www.arburg.com/en/

[11]http://www.nptel.ac.in/courses/Webcoursecontents/IIScBANG/Composite%20Materials/pdf/Lecture_Notes/LNm11.pdf