Method of recycling polyethylene terephthalate (PET) consumed bottles by extrusion spinning

Abstract

The present invention relates to a method of mechanical recycling of Polyethylene Terephthalate (PET) in the form of post-consumer bottles by Extrusion spinning with extrusion temperature of 270°, residence time 5 minutes, extrusion velocity 4.3 mm / min, dimensions of the spinneret are diameter of the capillary 1 mm, diameter of spinneret 12 mm, length of the spinneret 4 mm, rotational winding velocity 100 rot / min, lateral winding velocity 4.1 mm / min and diameter of spool 80 mm.

Description

[0001] METHOD OF RECYCLING POLYETHYLENE TEREPHTHALATE (PET) CONSUMED BOTTLES BY EXTRUSION SPINNING

[0002] Technical Field

[0003] An engineering project that is specifically related to the field of “General Mechanics and Sciences of Fibres”

[0004] Recycling is the ideal solution for The Global Energy Crisis|along with the Fatal Earth Pollution and the Life-Threatening climate changes. Researches never stop to obtain the best specifications from the obtainedrecyded material.

[0005] In the present project previously used bottles made of Polyethylene Terephthalate (PET) were recycled to obtain textile filaments with unique specifications making them a perfect choice in the textile field.

[0006] In the recycling industry the empty PET packaging that is discarded after use and became a waste is referred to as “post-consumer PET”

[0007] The major problem in post-consumer PET recycling is the polymer degradation, which is translated in the form of a decrease in the mechanical and physical properties of the final recycled product, and this was the / real challenge throughout the practical work that we successfully were able to overcome.

[0008] Background Art

[0009] Recycling can be simply defined as processing the wastes that can be re-used or in other words can be recycledwith specific procedures or processes to re-obtain the raw material that is then used to produce new products.

[0010] The Plastics Production Industry has been growing globally. Plastics are polymers obtained from fossil fuel-based chemicals like petroleum or natural gas. Plastics are composed of chains of polymers, the building unit of a polymer is a monomer, and thus, the polymer consists of repeated units of monomers that are bonded together through a process known as polymerization.

[0011] Thethree common ways of polyethylene terephthalate recycling are:

[0012] 1) Chemical Recycling

[0013] The chemical recycling method used with polyethylene terephthalate wastes is depolymerisation. Depolymerisation is the breaking down of the polymers that the plastic waste is made from to obtain the raw material in the form of monomers. The polymer is treated with a chemical to break the bonds between the polymer chains and obtain the monomers that make up the polymer. The commonly used chemicals are Ethylene glycol and methanol. The monomers are then purified through a process called distillation. The output is the raw material that isthen polymerised and now is ready for the production of a new plastic product.

[0014] The disadvantages of this recycling method are the high costs, the long duration to obtain the final recycled polymer and also being very dangerous because of the toxic and explosive materials used in the depolymerisation and distillation processes.

[0015] 2) Energy Recycling

[0016] Through incineration of the plastic waste the heat power released is used to obtain thermal and electric energy. Energy recycling is very popular in many countries but it requires huge investments and causes fatal pollution because of the emissions produced such as carbon dioxide, carbon monoxide and other toxic gases.

[0017] 3) Mechanical Recycling

[0018] Polyethylene terephthalate granules are obtained through an extrusion process. The plastic bottles are first crushed with a plastic crusher. The bottles caps and the labels are made from polyvinyl chloride (PVC) and polypropylene (PP); therefore, the crushed polymers are separated from each other. The most commonly used method is flotation technique which is a density-based technique where the crushed plastic is immersed in water. Polyethylene terephthalate and polyvinyl chloride flow to the bottom while polypropylene floats. Polyethylene terephthalate and polyvinyl chloride chips are then separated by infrared or x-rays, finally, the polyethylene terephthalate crushed chips are used to obtain recycled granules via the extrusion process.

[0019] Disclosure of Invention

[0020] The objective of this study is to valorize the wastes of Polyethylene Terephthalate (PET) in the form of post-consumer bottles, by mechanical recycling, to obtain textile filaments to be used in the textile industry. The initial material used was chips of post-consumer PET botles. These chips are used to obtain the filaments through the extrusion spinning (melt spinning) technique. Melting of the chips was regularly needed throughout the experimental work but the presence of water traces or humidity during the melting process leads to polymer degradation. The range of the melting point of PET is between 245 to 265 °C so it was totally safe for a thermal treatment to get rid of any water traces or humidity. The first step before using the chips during the experimental work was a thermal treatment in an over at an isotherm of 100 °C for 12 hours to avoid any hydro-thermo degradation. After the treatment, the chips are preserved in a desiccator containing silica acting as a drying agent that is used to prevent any humidity.

[0021] Extrusion spinning of the Polyethylene Terephthalate chips

[0022] The spinning technique used in this study is the extrusion spinning, also known as the melt spinning. The PET chips are fed into the oven to melt then they are pressed through or extruded out of a spinneret. The spinneret is a die principally used in filaments production. The molten polymer is pulled out of the capillaries (extruded through the capillaries) of the spinneret by applying a force on the molten polymer using a piston and the resulting long continuous filaments are solidified in the ambient air. The receiving unit for the extruded filaments was a spool where the filaments were woundaround the spool via a rotating winder.

[0023] According to the parameters used during spinning the characteristics of the filaments obtained change. During this study we were able to produce extremely high-quality filaments to be used in the textile industry.

[0024] The parameters to be adjusted in the spinning machine are:

[0025] • The extrusion temperature which is the temperature thtrt the chips are exposed to in the oven.

[0026] • The residence time which is the time the PET chips remain in the oven to melt before being extruded.

[0027] • The extrusion velocity which is the speed of the piston(extruding the molten polymer out of the capillary of the spinneret.

[0028] • The dimensions of the spinneret:

[0029] The diameter of the capillary

[0030] The diameter of the spinneret

[0031] The length of the spinneret

[0032] • The diameter of the spool that the produced recycled filaments are wound around.

[0033] • The rotating velocity of the winder holding the spool.

[0034] • The lateral velocity of the winder.

[0035] During the study several tests were carried out to finally / obtain the best parameters for the spinning process of the post-consumer PET chips.

[0036] To help determine the spinning parameters a study of the rheological and thermal behavior of the PET chips was done using a melt flow indexer.

[0037] Viscosity is a measure of a fluid’s resistance to flow, it can be thought of as a measure of the fluid’s thickness. In fluids, the molecules are attached together by intermolecular forces, the stronger these interaction forces are the more viscous the fluid is. When exposing a fluid to heat the intermolecular forces decrease and so the viscosity decreases. The more the heating temperature increases the more the forces decrease and thus the fluid becomes less viscous.

[0038] To determine the best extrusion temperature for the spinning process numerous rheological tests were carried out. At high temperatures the viscosity was too low and the extruded polymer was in a liquid form and we were unable to obtain any kind of solidified continuous filaments, what made it harder was that no cooling system was used to reduce the production costs; instead the cooling was in the ambient room temperature. On the contrary, at low temperatures the

[0039] fluid viscosity increases and we were unable to obtain continuous filaments with uniform diameter.

[0040] Not only doesthe extrusion temperaturehave a major role but also the residence time of the PET chips in the oven before being extruded out ismore critical. A short residence time results in large solid particles of the polymer because of the poor melting of the chips and a long residence time the extruded polymer was full of burnt parts and the polymer was degraded.

[0041] Several tests were carried out using the melt flow indexer to determine the previously mentioned critical factors; the extrusion temperature and the residence time. The range of the melting point of PET is between 245 to 265 °C so the tests were done at 260 °C, 270 °C, 275 °C and 280GC, they were not low to ensure aconvenient melting of the polymer and at the same time not very high to avoid the polymer degradation or burning. With those four different temperatures several tests using the indexer were carried out changing the residence time of the PET chips in the oven of the indexer before being extruded. for each of the previously mentioned temperatures a residence time of 1, 2, 3 and 4 minutes the extruded polymer was in the form of solid parts and the melting time was not long enough.

[0042] The tests for a residence time 5 minutes showed the following results:

[0043] • At 260 °Cthe extruded polymer was of high viscosity and the obtained polymer was in the form of soft polymer particles.

[0044] • At 280 °C the extruded polymer was with a low viscosity in a liquid form having brown traces of burnt polymer.

[0045] • At 275 °C the extruded polymer was with a convenient viscpsity but brown traces were observed indicating the burning of the polymer.

[0046] • At 270 °C the extruded polymer flowed with a convenient velocity and viscosity steadily without any brown traces.

[0047] Finally we concluded that the best extrusion temperature was|270 °C and the best residence time is 5 minutes.

[0048] Now, we can move to the extrusion spinning tests done on the spinning machine FILATECH that is designed to produce and wind filaments: via extrusion- winding technique. It is composed of three parts, an extruder, ^Winder and the controller of the machine. The controller’s role is to manage thp parameters of the extruder choosing the extrusion velocity' which is the velocity of the moving piston pressing on the molten polymer in the oven of the extruder to be extruded through the capillaries of the spinneret and the parameters of the winder. The factors that affect the filament properties related to the winding process, that are also adjusted through the controller are the rotational winding velocity and the lateral velocity of the winder which the lateral movement (to the right and to the left) of the spool, it is important for the distribution of the filament all over the length of the spool. The higher the rotational winding velocity the thinner the filaments are obtained.

[0049] “Two Extrusion Spinning were done using the FTLATECH machine”

[0050] • First Trial

[0051] > Extrusion Temperature = 270°C

[0052] > Residence Time = 5 min

[0053] > Extrusion Velocity = 4.3 mm / min

[0054] > Dimensions of the spinneret

[0055] Diameter of the capillary = 3 mm

[0056] Diameter of the spinneret = 11 mm

[0057] Length of the spinneret = 8 mm

[0058] > Rotational winding velocity = 100 rot / min = 25 m / min

[0059] > Lateral winding velocity = 4.1 mm / min

[0060] > Diameter of the spool = 80 mm

[0061] The filaments obtained were of a very poor quality. They were thick with an obvious diameter variation along the filaments. The diameter of the filaments measured 170-290 pm. The filaments were very britle; they broke when they were delicately stretched. The reason for these poor quality filaments was the wrong choice of the spinneret. Due to the large capillary diameter the filaments diameter was not uniform and they were relatively thicker than the desired output. They were also brittle due to their thickness because they were not fully solidified from the inside of the filament.

[0062] • Second Trial

[0063] > Extrusion Temperature = 270°C

[0064] > Residence Time = 5 min

[0065] > Extrusion Velocity = 4.3 mm / min

[0066] > Dimensions of the spinneret Diameter of the capillary ~ 1 mm

[0067] Diameter of the spinneret = 12 mm

[0068] Length of the spinneret = 4 mm

[0069] > Rotational winding velocity = 100 rot / min = 25 m / min

[0070] > Lateral winding velocity = 4.1 mm / min

[0071] > Diameter of the spool = 80 mm

[0072] The filaments obtained after extrusion were convenient and thiis they were furthertested with more accurate and precise techniques. A final precious postspin process was the filaments drawing. The filaments were drhwn to further decrease the diameter and increase the strength.

[0073] The polymer degradation was tested with an infrared characterization that showed that there was no polymer degradation during the recycling process.

[0074] The filaments were carefully inspected using an optical microscope before and after the drawing process, where the diameter measure and variation were the most important. Using the optical microscope 10 samples were tested to measure the diameter of the filaments. The diameter was measured at 15 different sections for each sample. Before the drawing process of the filaments the diameter was 100 ± 1μm. After the drawing of the fi laments the diameter was 40 ± 1μm.

[0075] Finally, various mechanical tests were done, where the most important was the fatigue test because this is the most effective factor during weaving, being in the form of a mono-filament, a yarn or a tow.

Claims

Claims1- The objective of this study is to valorize the wastes of Polyethylene Terephthalate (PET) in the form of post-consumer botles, by mechanical recycling, to obtain textile filaments to be used in the textile industry. The initial material used was chips of post-consumer PET bottles. These chips are used to obtain the filaments through the extrusion spinning (melt spinning) technique. We were able to obtain filaments with outstanding characteristics and properties and the extrusion spinning parameters used were:> Extrusion Temperature = 270°C> Residence Time = 5 min> Extrusion Velocity = 4.3 mm / min> Dimensions of the spinneretDiameter of the capillary = 1 mmDiameter of the spinneret = 12 mmLength of the spinneret = 4 mm> Rotational winding velocity = 100 rot / min = 25 m / min> Lateral winding velocity = 4.1 mm / min> Diameter of the spool = 80 mtnThe filaments obtained were of a diameter 40 ± 1μm

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