From post consumer packaging waste PET

Terephthalate (PET) consumption has continued to grow in recent years and the forecasts remain optimistic in this regard. As regards the recycled amount thereof, the trend is also bullish, though the State does not reach even European levels of recovery. On the other hand, applications that appears higher percentage of recycled material (fiber and strap) are still considered destinations in second in which the added value of the product is scarce, wasting a superb technical properties that characterize the material.

The results obtained during the implementation of a research project whose main objective is to enhance one of the main waste obtained from selective collection, mainly from bottles and packaging PET points are discussed in this article. The valorization of this product has been carried out through the development of a manufacturing process simple and economically profitable, based on conventional techniques of compounding, that allows to obtain compounds of engineering plastics suitable for demanding applications, such as parts of automobile, in which the mechanical properties, resistance to temperature and dimensional stability are essential.

The recovery of bottles of PET in Europe is growing continuously, hoping that this upward trend will continue in the coming years. Recovery forecasts are optimistic especially in countries such as Italy, Austria, Belgium, France and Switzerland in which recovery figures grow year after year. However, Spain is far still achieve their recovery rates. According to data from the European Association of recyclers of PET (Petcore), currently recovers, classifies and recycles approximately 25 per cent of the total number of bottles of PET in the European market.

In the figure above you can clearly see the trend on the rise of the recovery. This growth is happening exponentially, so it was to be hoped that the source of recycled PET (RPET) is increasing.

Following these trends the Gaiker technological centre has carried out a project whose goal is the revaluation of RPET, waste mainly comes from packaging and bottles, and turn it into a material with a performance similar to the reinforced Virgin PET of engineering. The project has received the grant of the Ministry of the environment.

Figura1. Recovery of bottles of PET in thousands of tonnes until 2003. (Source: PETCORE)

Engineering resins based on terephthalate (PET) are made from a polymer viscosity media which is chemically equivalent to those used in fibers, films and packaging. These ordinarily reinforced and filled with fiberglass, resins can be molded to produce structural parts with high impact resistance in domestic appliances and automotive. They also have many applications in other sectors such as construction, furniture, electrical and electronic, etc.

The PET can be considered a raw material for low-cost for the production of engineering compounds when compared with other polymers. The reason is that it is a readily available resource through the recycling of bottles of mineral water, and that in the future it will be even more due to the development and proliferation of the recycling of plastics in the world.

However, this polymer has a number of disadvantages compared to other thermoplastics engineering when the used transformation technique is the moulding by injection. The PET has a low crystallization speed, giving it a tendency to weaken, feature that has kept away this resin of the injection process. Other disadvantages which presents are its high sensitivity to moisture and low glass transition temperature. However, has a high mechanical module, high resistance to temperature and surface brightness, if present a suitable crystallization.

A correct formulation of the compound's PET can avoid the problems previously mentioned, through the use of additives and loads. For example, the incorporation of glass fibre increases the glass transition temperature and other polymer alloy improves the resistance to impact drastically.

Gaiker be developing composite injection PET and high performance from RPET from selective collection. Developed compounds can be used as resins of engineering in many demanding applications, proving that the use of PET packaging recycled feedstock provides a high quality and with high molecular weight polymer. In addition allows recycled RPET fractions with very high color or other disadvantages that prevent a direct recycling in transparent containers but which are not an issue in applications dull as that normally goes to find the PET as engineering resin compound.

In the early stages of the project or previously to the stages of compounding, made a selection of materials and a comparison between different additives and compounds likely to be employed in the development of formulations. Listed below are the components that have been used in the course of the project and its influence on various properties

Table1. Mechanical properties of the RPET and RPET with glass fibre

The capacity of an inorganic fiber reinforcement depends above all on their relationship aspect (length/diameter) and the stress of shear in the refuerzo-polímero interface. The fiberglass improves the module flexion, resistance to traction and temperature resistance. Thanks largely to the increase in its properties the PET combined with glass fibre can be considered an engineering plastic.

The properties of the RPET and a compound made with RPET and fiberglass to 30 per cent can be compared in the following table. The used fiber has been Vetrotex 952 4.5 millimeters long of Saint Gobain.

One of the major constraints of the PET is its low velocity of crystallization. Like other polymers with this feature, the polybut-1 for example, the PET accurate long cycle times to get the enough crystallinity. This fact makes it little suitable for use in injection. In addition, in the case of the PET generated crystal structure presents a size of large Crystal, which tends to generate certain mechanical fragility in the moulding. The amorphous PET softens to a temperature of only 80. The crystallinity provides improvement in thermal and mechanical, necessary resistance for the majority of the uses that may have an engineering polymer (1). The PBT, another polyester that has a fast crystallization speed, more commonly used in injection for this reason.

Alkaline salts of carboxylic acids of high molecular weight are very effective as nucleators for PET. These salts can be distributed very homogeneously and at low concentrations throughout the polymer, which makes them more effective.

The polieteréster also act as nucleating and promoters of crystallization. These are plasticizers fluids that reduce Intermolecular forces between polymer chains, and allowing a greater shift between these, and can then sort is the most favourable for the formation of the Crystal.

Table2. Mechanical properties of RPET and RPET with impact modifiers

The impact resistance can be improved by introducing a material elastomeric able to absorb the shock wave produced by an impact energy and dissipate this energy without causing fractures in the polymer matrix. An effective way to improve the impact resistance is through the dispersion of a rubber in heterogeneous phase within the matrix of PET. The effect of the particles of rubber is to induce a mechanism of general deformation in the material, rather than a localized effect, thus increasing the amount of energy dissipated in the fracture. The effectiveness of the modifier depends on:

• The nature of the elastomer.

• Amount of elastomer.

• Dispersion of rubber particle size.

• Distance interpartícula.

There are modifiers to impact reactive and non reactive. The first are best because they form a dispersed phase stable because they are anchored to the matrix of PET. Non-reactive modifiers can disperse efficiently through an intensive processing, but tend to coalescer later. The selected switches have been:

• Paraloid EXL 5136.

• Paraloid EXL 2314.

The first is a non reactive modifier, but is a MBS with very good behaviour because it leads to particles with a blessedly core of butadiene-styrene, coated with a rigid shell of methacrylate-styrene. The result is a good impact behavior without changing the mechanical and thermal properties of PET greatly. The second is a reactive modifier acrylic. The combination of the two is important since the second provides an anchor of the elastomer matrix of the PET, which allows a better spread of tensions to everything.

Below is the improvement caused by these additives in impact and the effect thereof in formulations based on RPET. In addition to the increase in the impact resistance observed in tensile behavior changes confirm the flexibility provided by this kind of additives.

These agents are used to increase molecular weight that can be diminished through hydrolysis in reprocessing. Coupling agents have at least two functional groups able to cause reactions in addition to the groups terminal of the polymeric resin: hydroxyl (OH) and carboxyl (COOH) selected coupling agents are the Bisphenol in diepoxido (2), the dianhidrido piromelitico (3) and (4) trifenilfosfito

Below is the influence of these agents on the properties of the material.

Identified additives have been developed different formulations using the double available in the Center technological Gaiker screw extruder. Later test tubes for the execution of the tests of characterization, whose results are reflected in the tables above have been injected. In this way been able to define the properties of these compounds and determining the influence of each of the additives. Once selected additives that best properties provide the RPET, the proportion in which every one should be added to form the new compound has been specified.

Tabla3. Mechanical properties of RPET and RPET with coupling agents

Table 4. Variation in properties with regard to the commercial material.

With the results obtained in the previous tasks developed in Gaiker a formulation contratipo of commercial material. To determine the improvement or loss of properties of the new product have been compared their mechanical properties with which presented the commercial material and a mixture of RPET exclusively reinforced with glass fibre. In this way is intended to separate the influence that might have the fiberglass of the features provided by the various incorporated additives.

Thus, in the double screw extruder formulations in the form of pellets, both the compound and a mixture of RPET have been obtained and fibreglass-free of additives. With these formulations as well as the commercial material (530 Rynite DuPont) test tubes have been injecting that characterized once they have served to compare with other materials.

The following table as they vary the properties of the test tubes injected with the created compound and RPET fibre by reference to the properties of the test tubes injected with commercial PET can be.

As you can see the mix of RPET and fiberglass presents a loss of important features to the commercial PET. However, the addition of additives in the compound substantially improves the properties so that the loss of traction characteristics is not as important. Even the compound exceeds considerably the impact of the commercial PET properties. Thus one can conclude that the additives added clearly improve the properties of the recycled PET.

Once proven improvement in test tubes at a pilot scale is selected a piece to inject it with different materials: the compound created in the Center technological Gaiker, the RPET exclusively reinforced with glass fibre and the commercial PET Rynite. The injected parts are cylinder, open on one side while the other is closed by a grid. Aesthetically, the parts injected with different materials differ between them by color. As you can see in the figure below, the piece injected with commercial material acquires a crude colour, while the injected with the compound offers a grayish color and the injected with RPET more green fiberglass.

These pieces have been characterized by compression and ball-impact tests and have been subjected to trials of chemical resistance, heat resistance and ageing. After the trials have been characterized and has been observed behavior that offer parts with different treatments

The results of the tests carried out corroborate the greater flexibility of the compound developed in Gaiker versus the commercial product. Thus, parts injected with the compound improves the properties of impact on the commercial material (38,46%), while decreases its resistance to compression (25,05%) However, it should be noted that the parts of the compound formed by RPET and fiberglass offer some features similar to those offered by the parts injected with material commercial.

The compound, despite offering a lower resistance to compression is able to withstand higher impact strength, while parts of RPET and fiberglass resists compression in a similar way that the commercial parts and only increases their ability to impact resistance.

As mentioned previously have undergone to the parts to different treatments:

• Aging: 80 ° C for 1 week

• Heat resistance: 150 ° C for 24 hours

• Chemical resistance: immersion during 1 week in different media: oil and gas

Figure 2. Injected parts. From left to right: commercial PET, compound and RPET + fv

Figure 3. Test of compression.

Figure 8. Breakage in compression. From left to right: compound, RPET + fv and commercial PET.

The effect of high temperatures and chemical compounds exert on the resistance to compression of the pieces can be seen in the next table.

The developed compound seems less sensitive to employed treatments. Notable variations occur with heat resistance test, i.e. high temperatures (150ºc) affect the properties of the pieces: in the case of the commercial PET and glass fibre RPET resistance to compression decreases by 10 percent while the case of the compound resistance increases at a 13 per cent.

Table 5. Variation of resistance to compression with the pieces once treated.

Figure 4. Comparison of the properties of the pieces made with the compounding and Pet + fv with the properties of the pieces made with Virgin Pet trade

Figure 7. Comparison of the behavior of the material by compression

• The created compound has a greater impact than the commercial PET resistance, which means that our material is more ductile.

This feature is also reflected in lower resistance to compression that presents the compound which, instead of reaching out to break as the commercial PET, is deformed with a more flexible behavior. This behavior can be seen in the following chart of compression and the image of the figure 8 outlining the different behaviors of the pieces

• High temperatures (150ºc) have an impact on the resistance to compression of the pieces.

In the case of the commercial PET and glass fibre RPET resistance decreases, whereas in the case of the compound the resistance increases. Compound pieces become more fragile and, despite increasing its resistance to traction, his behavior to compression is much more affected than the behavior of the rest of pieces.

• The compound features acceptable properties for the current market in the automotive sector as in other sectors.

This material enhances some of the properties of the Virgin PET trade, this represents added value, the RPET is an easy and inexpensive material for and the process for the manufacture of this material is simple and cost-effective.

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