How to Dissolve PET Bottles?

PET bottles are everywhere in our daily lives. In the morning, when you open a bottle of mineral water to nourish your thirsty throat; In the afternoon, open a bottle of carbonated beverage and enjoy the refreshing bubbling sensation; Or when organizing your home, you may come across plastic storage bottles filled with various items. These bottles are mostly made of polyethylene terephthalate (PET). PET bottles are widely used in various fields such as beverages, food, daily chemical products, pharmaceuticals, etc. due to their advantages of light weight, transparency, high strength, good airtightness, and low cost. According to statistics, billions of PET bottles are produced worldwide each year.

However, with the widespread use of PET bottles, the issue of disposing of waste PET bottles has become increasingly prominent. A large number of discarded PET bottles are piled up like mountains, not only occupying a large amount of land resources, but also their degradation process is extremely slow, taking hundreds of years to fully decompose in the natural environment, which puts great pressure on the environment. In order to achieve sustainable use of resources and environmental protection, it is urgent to recycle and reuse PET bottles. In the process of recycling and reusing, dissolving PET bottles is a key step that determines the efficiency of recycling and the quality of recycled products. Therefore, exploring how to effectively dissolve PET bottles has important practical significance.

I. In Depth Analysis of PET

1. Chemical Structure of PET

   PET， Polyethylene terephthalate, with a chemical structural formula of – [OC Ph-COOCH ₂ CH ₂ O -] – (Ph is the benzene ring), is obtained by esterification and condensation of terephthalic acid (PTA) and ethylene glycol (EG). From a molecular structure perspective, it is a linear polymer composed of rigid benzene rings, flexible ethylene segments, and ester groups. This structure endows PET with unique properties. The presence of benzene ring increases the rigidity of the molecular chain, making it have better strength and stability; The ethylene chain segment provides a certain degree of flexibility; The polarity of ester groups makes PET have a certain affinity for certain polar solvents, but at the same time, it also makes it prone to hydrolysis in high temperature and high humidity environments.

   The crystallinity of PET molecules is also one of its important characteristics. Under normal circumstances, PET molecular chains are in a straight chain configuration, with the benzene rings on the large molecular chains almost in the same plane. This regular conformation is conducive to tight stacking between molecules, thereby giving PET good crystallization ability. When the melt slowly cools, PET will form a milky white crystalline polymer with high crystallinity; When rapidly cooled, a transparent amorphous structure will be obtained. The degree of crystallinity has a significant impact on the performance of PET. PET with high crystallinity will improve its hardness, strength, heat resistance, and other properties, but its transparency and flexibility will decrease.

2. Physical Properties of PET

   In terms of physical properties, PET exhibits many characteristics. It has a high melting point, usually around 250-260 ℃, which makes PET have good thermal stability at room temperature and can maintain its solid state. Its glass transition temperature is about 67-81 ℃. Below the glass transition temperature, PET exhibits rigidity and brittleness similar to glass; Above the glass transition temperature, the activity of PET molecular chains increases, and the material gradually becomes softer and more malleable.

   The density of PET is about 1.38g/cm ³, which is relatively light, and this is also one of the reasons why it is widely used in the packaging field. It also has good mechanical properties, such as high tensile strength, bending strength, and modulus, which can withstand certain external forces without deformation or rupture. In addition, PET has high transparency and a visible light transmittance of about 87%. The bottles made from PET can clearly display the internal products and attract consumers’ attention.

   However, these physical properties of PET also determine that it is difficult to dissolve at room temperature. The interaction force between its molecular chains is strong, and the presence of crystalline regions makes it difficult for solvent molecules to penetrate into the interior of the molecules, disrupting the intermolecular interactions. Moreover, PET has high chemical stability, and it is difficult for general solvents to undergo chemical reactions with it at room temperature, thus achieving dissolution.

II. Searching for the Key to Dissolve PET Bottles

1. Attempt at Common Organic Solvents

   In the process of exploring PET bottle dissolution methods, we first think of common organic solvents. Organic solvents such as ethanol, acetone, and toluene are widely used in fields such as organic synthesis and cleaning, and their molecular structures and properties vary. Ethanol molecules contain hydroxyl groups and have a certain polarity, which can form hydrogen bonds with water molecules, making them excellent in dissolving some polar substances; Acetone has a relatively simple molecular structure, strong volatility, and solubility, and is commonly used to dissolve some organic resins; Toluene is a typical aromatic hydrocarbon organic solvent with strong non-polar properties and good solubility for some non-polar organic compounds.

   However, when we try to dissolve PET bottles with these common organic solvents, it is often difficult to achieve the desired effect. From the perspective of intermolecular forces, PET molecular chains exhibit strong van der Waals forces and hydrogen bonding interactions, and the regular structure of their crystalline regions also increases the strength of intermolecular interactions. However, the interaction force between molecules of common organic solvents and PET molecules is weak, which cannot effectively disrupt the interaction between PET molecular chains and disperse PET molecules into the solvent. For example, although ethanol has polarity, its polarity does not match well with the polarity of ester groups in PET molecules, making it difficult to overcome the intermolecular forces between PET molecules; Although acetone has strong volatility, its solubility in PET is limited. Even under heating conditions, it can only cause slight swelling of PET and cannot achieve complete dissolution; The non-polar structure of toluene does not match the partially polar structure of PET molecules, and the interaction between the two is weak, making it almost impossible to dissolve PET.

2. Special Solvents Appear

   Since common organic solvents are unable to handle the task of dissolving PET bottles, special solvents are needed to ‘come on stage’. Among numerous special solvents, hexafluoroisopropanol (HFIP) and phenol/tetrachloroethylene mixed solvents stand out as the ‘capable assistants’ for dissolving PET.

   Hexafluoroisopropanol is a fluorinated organic solvent with multiple fluorine atoms in its molecular structure, which endows it with unique physical and chemical properties. From the perspective of dissolution principle, the fluorine atoms in hexafluoroisopropanol molecules have strong electronegativity, making the molecules highly polar. At the same time, their molecular structure has a large steric hindrance, which can effectively disrupt the interactions between PET molecular chains. When PET bottles come into contact with hexafluoroisopropanol, hexafluoroisopropanol molecules can quickly penetrate between PET molecular chains, forming strong intermolecular forces with PET molecules, such as hydrogen bonds, dipole dipole interactions, etc., gradually breaking down the interactions between PET molecular chains and dispersing PET molecules into hexafluoroisopropanol, thereby achieving dissolution. Experiments have shown that at room temperature, by adding PET fragments to hexafluoroisopropanol and stirring for a period of time, PET can gradually dissolve and form a uniform solution.

   Phenol/tetrachloroethylene mixed solvent is also a commonly used system for dissolving PET. Phenol molecules contain hydroxyl groups and have a certain polarity, which can form hydrogen bonds with ester groups in PET molecules; Tetrachloroethane is a highly non-polar organic solvent that can interact with the benzene ring in PET molecules through van der Waals forces. The synergistic effect of polar and non-polar solvents enables the phenol/tetrachloroethylene mixed solvent to effectively disrupt the intermolecular interactions of PET molecules and achieve the dissolution of PET. Generally speaking, phenol and tetrachloroethylene are mixed in a certain ratio (such as 1:1), heated to a certain temperature (80-100 ℃), and then PET bottle fragments are added. Under stirring conditions, PET will gradually dissolve.

   There are many conditions and precautions to pay attention to when using these special solvents to dissolve PET bottles. Firstly, there is the temperature condition. Although hexafluoroisopropanol can dissolve PET at room temperature, increasing the temperature appropriately (40-60 ℃) can accelerate the dissolution rate and improve the dissolution efficiency. For phenol/tetrachloroethylene mixed solvents, it is necessary to heat them to a higher temperature (80-100 ℃) to achieve good dissolution effect, but attention should be paid to controlling the temperature not too high, otherwise it may cause problems such as rapid solvent evaporation and PET molecule degradation.

   Secondly, there is a safety issue. Hexafluoroisopropanol has certain toxicity and corrosiveness, and must be used in a well ventilated environment. Personal protective equipment such as protective gloves and goggles should be worn to avoid skin contact and inhalation of vapors. Phenol is corrosive and toxic, and has a strong irritant effect on the skin and mucous membranes. Extra caution should be taken during use; Tetrachloroethane is also a toxic organic solvent and flammable. It should be kept away from sources of fire and heat to prevent fire and explosion accidents.

   Furthermore, the recovery and recycling of solvents are also factors that need to be considered. These special solvents are often expensive. In order to reduce costs and minimize environmental impact, after dissolving PET, the solvents should be recycled and reused as much as possible. Distillation, extraction, and other methods can be used to separate the solvent from the dissolved PET. The recovered solvent can be purified and reused for PET dissolution.

III. Complete Record of Dissolution Experiment

1. Preparation Phase

   Adequate and thorough preparation is crucial before conducting PET bottle dissolution experiments. Firstly, for material preparation, we need to collect a certain number of PET bottles. In order to ensure the accuracy and reproducibility of the experimental results, it is best to choose PET bottles of the same brand and specification, such as the common 500ml mineral water bottle. Thoroughly clean the collected PET bottles to remove surface dirt, labels, and other impurities. You can first rinse the PET bottle with clean water, then soak it in an appropriate amount of detergent for a period of time, carefully brush it with a brush, and finally rinse it thoroughly with a large amount of clean water to ensure that there are no residual impurities on the surface of the bottle. Afterwards, cut the cleaned PET bottle into evenly sized fragments for easy subsequent dissolution operations. The size of the fragments is generally controlled at around 1-2 square centimeters.

   The choice of solvent is also crucial. In this experiment, we used a mixture of hexafluoroisopropanol and phenol/tetrachloroethylene solvent (phenol and tetrachloroethylene mixed in a 1:1 volume ratio). Due to the toxicity and corrosiveness of both solvents, it is necessary to accurately measure and store them in a sealed glass container according to the required amount for the experiment to avoid solvent evaporation and leakage. At the same time, it is necessary to ensure that the purity of the solvent meets the experimental requirements to avoid impurities affecting the dissolution effect.

   In terms of experimental equipment, it is necessary to prepare a reaction vessel with heating and stirring functions. The material of the reaction vessel should be corrosion-resistant and able to withstand the erosion of solvents. Its volume depends on the scale of the experiment, and generally 2-5 liter reaction vessels are suitable for medium-sized experiments. High precision thermometers should also be equipped to accurately measure the temperature during the reaction process, covering the temperature range required for the experiment with an accuracy of ± 1 ℃. In order to accurately measure solvents and record experimental data, instruments such as measuring cylinders, pipettes, electronic balances, stopwatches, etc. need to be prepared.

   Safety protection preparation cannot be ignored. Throughout the entire experiment, protective gloves must be worn, and the glove material should be able to effectively resist the corrosion of hexafluoroisopropanol and phenol/tetrachloroethylene, such as nitrile rubber gloves. Goggles are also essential as they can protect the eyes from solvent splashes. In addition, the experiment should be conducted in a fume hood to ensure good ventilation and timely discharge of volatile toxic solvent vapors to prevent operators from inhaling poisoning. The ventilation volume of the fume hood should meet the experimental requirements, and the operation status of the ventilation system should be regularly checked to ensure its normal operation.

2. Operating Steps

   When all the preparations are ready, the dissolution experiment can begin. Firstly, place the reaction kettle on a stable experimental platform, connect the heating and stirring devices, and ensure that each device can operate normally. Then, accurately measure an appropriate amount of hexafluoroisopropanol or phenol/tetrachloroethylene mixed solvent using a pipette and add it to the reaction vessel. If hexafluoroisopropanol is used, the solvent is generally added in a ratio of 1:10-1:15 by mass of PET fragments to hexafluoroisopropanol; If phenol/tetrachloroethylene mixed solvent is used, due to its relatively weak solubility, the mass ratio of PET fragments to the mixed solvent can be controlled at 1:15-1:20.

   Turn on the stirring device and set the stirring speed to 100-200 revolutions per minute to create a uniform flow of solvent in the reaction vessel, creating favorable mass transfer conditions for the subsequent dissolution process after adding PET fragments. While stirring, slowly add the cut PET bottle fragments into the reaction vessel, paying attention to evenly dispersing them to avoid local accumulation of PET fragments that may affect the dissolution effect. The process of adding PET fragments should continue until the predetermined amount is reached.

   If hexafluoroisopropanol is used as the solvent, the dissolution reaction can be carried out at room temperature. However, to accelerate the dissolution rate, the temperature of the reaction vessel can be slowly increased to 40-60 ℃. The heating process should be carried out slowly, and the heating rate is generally controlled at 1-2 ℃ per minute to avoid adverse effects of rapid temperature changes on the dissolution process. When the temperature reaches the set value, maintain constant temperature stirring and continuously observe the dissolution of PET fragments.

   If phenol/tetrachloroethylene mixed solvent is used, the reaction kettle needs to be heated to 80-100 ℃. Similarly, the heating process should be slow. After reaching the set temperature, maintain the stirring state and closely monitor the dissolution process of PET fragments in the mixed solvent. During the entire dissolution process, key data such as reaction time, temperature, and changes in solution state should be recorded regularly for subsequent analysis of experimental results. Generally, data is recorded every 10-15 minutes, while observing the degree of dissolution of PET fragments, such as changes in fragment size and solution transparency.

   When the PET fragments are completely dissolved and the solution becomes uniform and transparent, stop stirring and heating, and let the reaction vessel cool naturally to room temperature. During the cooling process, the solution may exhibit slight turbidity due to a decrease in temperature causing partially dissolved PET molecules to re aggregate, but this does not affect subsequent analysis and processing.

3. Analysis of Experimental Phenomena and Results

   In the experiment of dissolving PET bottles with hexafluoroisopropanol, when PET fragments were first added, due to the incomplete establishment of the interaction between hexafluoroisopropanol molecules and PET molecules, the PET fragments floated on the surface of the solvent without significant changes. As the stirring progresses, hexafluoroisopropanol molecules gradually penetrate between the PET molecular chains. After about 5-10 minutes, PET fragments begin to swell, with their volume gradually increasing and their edges becoming blurred. As time goes by, the swollen PET fragments are gradually dispersed into hexafluoroisopropanol, and the transparency of the solution gradually decreases, presenting a milky white turbid state. At a temperature of 40-60 ℃, after about 30-60 minutes, the PET fragments completely dissolve and the solution becomes a uniform and transparent light yellow liquid.

   In the experiment of using phenol/tetrachloroethylene mixed solvent to dissolve PET bottles, the dissolution process of PET fragments was relatively slow under heating and stirring conditions of 80-100 ℃. At the beginning, PET fragments also float on the surface of the mixed solvent. As the temperature increases and stirring continues, about 15-20 minutes later, the PET fragments begin to swell and the surface becomes rough. Due to the relatively weak solubility of phenol/tetrachloroethylene mixed solvents in PET, it takes longer to disrupt the intermolecular interactions of PET molecules. It takes about 60-90 minutes for PET fragments to fully dissolve, and the solution appears in a light brown transparent state.

   Through the analysis of experimental phenomena and results, we can find that temperature has a significant impact on the dissolution process of PET. Both hexafluoroisopropanol and phenol/tetrachloroethylene mixed solvents can accelerate the dissolution rate of PET by increasing the temperature. This is because as the temperature increases, the thermal motion of molecules intensifies, and the interaction between solvent molecules and PET molecules increases, which can more quickly disrupt the interaction between PET molecular chains and disperse PET molecules into the solvent more quickly.

   In addition, the type and proportion of solvents are also important factors affecting the dissolution effect of PET. Hexafluoroisopropanol has strong solubility and can quickly dissolve PET at relatively low temperatures; Although phenol/tetrachloroethylene mixed solvents can also dissolve PET, the dissolution rate is slower and requires higher temperatures and longer time. This is due to the different interaction modes and strengths between them and PET molecules. The fluorine atoms in hexafluoroisopropanol molecules endow them with strong polarity and special spatial structure, enabling them to better interact with PET molecules.The crystallinity and impurity content of PET bottles can also affect the dissolution process. PET bottles with higher crystallinity have more regular molecular chain arrangement, stronger intermolecular interactions, and relatively greater difficulty in dissolution, requiring longer time and higher temperature to fully dissolve; PET bottles containing more impurities may hinder the contact between solvent molecules and PET molecules, reducing the dissolution rate and effectiveness.

IV. Key Factors Affecting Dissolution Efficiency

1. The Wonderful Effect of Temperature

   Temperature plays a crucial role in the dissolution process of PET bottles, as it significantly affects the dissolution rate and effectiveness. At the molecular level, as the temperature increases, the thermal motion of molecules intensifies. For PET molecules and solvent molecules, higher temperatures increase their kinetic energy, leading to more frequent and intense collisions between molecules. This enables solvent molecules to penetrate more quickly between PET molecular chains, effectively disrupting the interactions between PET molecular chains, such as van der Waals forces and hydrogen bonds, thereby accelerating the dissolution rate of PET.

   When using hexafluoroisopropanol to dissolve PET bottles, although dissolution can also be achieved at room temperature, increasing the temperature to 40-60 ℃ will significantly accelerate the dissolution rate. Relevant experimental data shows that at room temperature, complete dissolution of PET may take several hours, while at temperatures of 40-60 ℃, it can be completely dissolved in about 30-60 minutes. When using a phenol/tetrachloroethylene mixed solvent, the effect of temperature is more significant. The mixed solvent can only dissolve PET well at a temperature of 80-100 ℃. If the temperature is below 80 ℃, the dissolution rate will be extremely slow, and it may not even dissolve completely; When the temperature exceeds 100 ℃, although the dissolution rate may further accelerate, it also increases the risk of solvent evaporation and PET molecule degradation.

   However, higher temperatures are not necessarily better. When the temperature is too high, PET molecules may undergo degradation reactions. The ester bonds in PET molecules are prone to breakage at high temperatures, resulting in shorter molecular chains and reduced molecular weight, thereby affecting the performance of regenerated PET. For example, when the temperature exceeds 200 ℃, the degradation rate of PET molecules significantly accelerates, and the strength, toughness, and other properties of recycled PET will significantly decrease, which cannot meet the requirements of subsequent processing and application. Moreover, excessively high temperatures can accelerate the evaporation rate of solvents, resulting in not only waste of solvents but also potential safety issues. For example, when using flammable solvents, the vapor formed by solvent evaporation at high temperatures may mix with air and explode when exposed to open flames.

   Therefore, when dissolving PET bottles, it is necessary to strictly control the temperature within an appropriate range according to the type of solvent used. For hexafluoroisopropanol, 40-60 ℃ is a suitable temperature range; For phenol/tetrachloroethylene mixed solvents, 80-100 ℃ is an ideal temperature range. In practical operation, high-precision temperature control equipment, such as heating devices with PID control function, can be used to precisely control the reaction temperature, ensuring the smooth progress of the dissolution process and the stability of the dissolution effect.

2. The Cumulative Effect of Time

   The dissolution time is another important factor affecting the degree of PET dissolution, and there is a close relationship between it and the degree of dissolution. In the initial stage of dissolution, as time goes on, solvent molecules continuously interact with PET molecules, gradually disrupting the interactions between PET molecular chains. PET molecules gradually disperse into the solvent, and the degree of dissolution continues to increase.

   Taking the dissolution of PET with hexafluoroisopropanol as an example, within the first 10-15 minutes, PET mainly undergoes swelling, gradually increasing in volume, and the degree of dissolution is relatively low; As time goes on, after about 30-60 minutes, the PET fragments completely dissolve and the solution becomes uniform and transparent, reaching a high degree of dissolution. When using phenol/tetrachloroethylene mixed solvents, due to their relatively weak solubility, the dissolution time needs to be longer. It takes about 60-90 minutes for PET to fully dissolve under conditions of 80-100 ℃.

   If the dissolution time is too short, PET molecules cannot fully interact with solvent molecules, and complete dissolution cannot be achieved. Unsolved PET will exist in the solution in the form of particles or blocks, which not only affects the uniformity and stability of the solution, but also has adverse effects on subsequent processing and applications. For example, when using dissolved PET solution to prepare regenerated fibers, undissolved PET particles may cause quality problems such as fiber breakage and uneven thickness.

   On the contrary, prolonged dissolution time is not a good thing. Excessive dissolution time can lead to reduced production efficiency and increased production costs. Moreover, prolonged exposure to high temperatures and solvent environments may cause degradation reactions of PET molecules, leading to chain breakage and a decrease in molecular weight, thereby reducing the performance of regenerated PET. Research has shown that when the dissolution time exceeds a certain limit, the tensile strength, elongation at break, and other performance indicators of recycled PET will significantly decrease.

   Therefore, in practical operation, it is necessary to control the dissolution time reasonably based on factors such as solvent type, temperature, and the characteristics of PET. Generally speaking, while ensuring complete dissolution of PET, the dissolution time should be shortened as much as possible to improve production efficiency and ensure the quality of recycled PET. The optimal dissolution time under different conditions can be predetermined through experiments and strictly followed during the production process.

3. Subtle Balance of Solvent Ratio

   The solvent ratio plays a crucial role in the dissolution process of PET bottles, as it directly affects the dissolution effect. Different solvent ratios can cause changes in the interaction mode and strength between solvents and PET molecules, resulting in different dissolution situations.

   Taking phenol/tetrachloroethylene mixed solvent as an example, when the ratio of phenol to tetrachloroethylene is 1:1, PET can be dissolved well. This is because the hydroxyl groups in phenol molecules have a certain polarity and can form hydrogen bonds with the ester groups in PET molecules; Tetrachloroethane is a highly non-polar organic solvent that can interact with the benzene ring in PET molecules through van der Waals forces. The synergistic effect of polar and non-polar solvents enables a 1:1 ratio mixed solvent to effectively disrupt the interactions between PET molecular chains and achieve the dissolution of PET.

   However, when the solvent ratio changes, the dissolution effect will be significantly affected. If the proportion of phenol is too high, the polarity of the mixed solvent will increase. Although the interaction with the ester group in PET molecules may be enhanced, the interaction with the benzene ring will be relatively weakened, resulting in a decrease in the overall solubility. On the contrary, if the proportion of tetrachloroethylene is too high, the non-polar nature of the mixed solvent will be enhanced, and the interaction with the benzene ring in PET molecules will be strengthened, but the interaction with the ester group will be weakened, which will also affect the dissolution effect.

   When using hexafluoroisopropanol to dissolve PET, although it is a single solvent, the mass ratio of PET to hexafluoroisopropanol can also affect the dissolution. Generally speaking, when the mass ratio of PET fragments to hexafluoroisopropanol is 1:10-1:15, a better dissolution effect can be achieved. If the proportion of PET is too high, exceeding the solubility range of hexafluoroisopropanol, it will cause some PET to be unable to dissolve; If the proportion of hexafluoroisopropanol is too high, although it can ensure complete dissolution of PET, it will cause waste of solvent and increase costs.

   In addition, the solvent ratio can also affect the properties of the solution after dissolution. Different solvent ratios may cause changes in the viscosity, stability, and other properties of the solution. For example, when the solvent ratio is not appropriate, the dissolved solution may have a high viscosity, which is not conducive to subsequent filtration, transportation, and other operations; Or the stability of the solution may be poor, leading to phenomena such as stratification and precipitation.

   Therefore, when dissolving PET bottles, it is necessary to strictly control the solvent ratio. Based on the characteristics of the solvent and the properties of PET, the optimal solvent ratio should be determined through experiments to ensure good dissolution effect and subsequent processing performance. In actual production, high-precision measuring equipment can be used to accurately measure solvents and ensure the accuracy of solvent ratios.

V. Safety and Environmental Protection Cannot be Ignored

1. Safety Protection for Solvent Use

   In the process of dissolving PET bottles, both hexafluoroisopropanol and phenol/tetrachloroethylene mixed solvents have certain toxicity and corrosiveness, so safety precautions are crucial. When using these solvents, operators must wear comprehensive protective equipment. Protective gloves should be made of nitrile rubber gloves with good chemical corrosion resistance, which can effectively block the contact of solvents with the skin, prevent the skin from being corroded and absorbing toxic substances. Goggles should have splash proof function, which can fully protect the eyes and prevent solvents from splashing into the eyes, causing serious injuries such as eye burns. At the same time, in order to prevent inhalation of toxic solvent vapors, one should wear a gas mask and choose a suitable canister to ensure effective filtration of harmful gases in the air.

   The operation process must be carried out in a well ventilated environment, and a fume hood is an essential equipment. A fume hood can promptly discharge volatile solvent vapors outdoors, reduce the concentration of harmful gases indoors, and ensure the respiratory safety of operators. The ventilation rate of the fume hood should be adjusted reasonably according to the experimental scale and solvent evaporation. Generally, the wind speed inside the fume hood is required to reach 0.5-1.0 meters per second to ensure effective discharge of solvent vapor. Before using a fume hood, check if its ventilation system is functioning properly and if the ventilation ducts are unobstructed to avoid the accumulation of harmful gases due to ventilation failures.

   In addition, first aid equipment and medication should be provided at the operation site, such as physiological saline for eye flushing and ointment for treating skin burns. Once unexpected situations such as solvent contact with skin or eyes occur, emergency treatment can be carried out in a timely manner to reduce the degree of injury. At the same time, operators should receive relevant safety training, familiarize themselves with the properties of solvents, safety operating procedures, and emergency response methods, and improve their safety awareness and emergency response capabilities.

2. Environmentally Friendly Treatment of Dissolved Products

   The products generated after dissolving PET bottles, including the dissolved PET solution and residual solvents, need to be properly treated for environmental protection to reduce pollution to the environment. For the dissolved PET solution, if it needs to be recycled, it needs to be separated and purified first. Impurities in the solution can be removed by filtration, centrifugation, and other methods, and then the solvent can be separated from PET through distillation, extraction, and other techniques. The recovered solvent can be purified and reused for PET dissolution, achieving solvent recycling, reducing costs, and minimizing solvent emissions.

   For PET products that cannot be reused, pyrolysis or incineration treatment can be considered, but attention should be paid to controlling the conditions during the treatment process to reduce the generation of harmful gases. Pyrolysis is the process of heating and decomposing PET into small molecule compounds under anaerobic or hypoxic conditions, which can be further utilized as chemical raw materials. Incineration treatment involves burning PET at high temperatures, releasing heat energy, but the combustion process may produce harmful gases such as carbon dioxide, carbon monoxide, nitrogen oxides, dioxins, etc. In order to reduce the emissions of these harmful gases, advanced incineration technology and tail gas treatment equipment are needed, such as efficient desulfurization, denitrification, dust removal devices, and dioxin removal devices, to ensure that the tail gas emissions meet the standards.

   Residual solvents should not be discharged arbitrarily and should be treated according to their properties. For recyclable solvents, they should be recycled and reused; For solvents that are difficult to recycle, appropriate methods should be used for harmless treatment, such as chemical oxidation, biodegradation, etc. Chemical oxidation method is the use of strong oxidants to oxidize and decompose solvents into harmless substances; The law of biodegradation is to use the metabolic process of microorganisms to decompose solvents into harmless products such as carbon dioxide and water.

   Throughout the entire dissolution and treatment process, relevant environmental regulations and standards should be followed, a sound environmental management system should be established, and environmental monitoring of the production process should be strengthened to ensure that the emissions of various pollutants meet national and local environmental requirements. At the same time, we should actively explore more environmentally friendly and efficient PET dissolution and processing technologies to promote the sustainable development of the PET recycling and reuse industry.

VI. Application Expansion and Prospect Outlook

1. Potential Value in the Field of Scientific Research

   Dissolved PET bottles have significant potential value in the field of scientific research, providing strong support for in-depth research and innovative development in materials science. In terms of material performance research, by dissolving PET and preparing it into different forms such as films, fibers, etc., the relationship between the microstructure and macroscopic properties of PET can be further explored. For example, the dissolved PET solution is prepared into a thin film by casting method, and its mechanical and optical properties are studied under different stretching ratios. Due to the dissolution process, PET molecules can be fully dispersed, resulting in a more uniform structure of the prepared film. This allows for a more accurate study of the effects of molecular orientation, crystallinity, and other factors on performance.

   In terms of new product development, dissolving PET has opened up new avenues for the research and development of new composite materials. Researchers can composite the dissolved PET with other functional materials such as nanoparticles, bioactive molecules, etc. to endow the material with new properties. For example, adding nano silver particles to a dissolved PET solution can prepare PET composite materials with antibacterial properties, which have potential application value in fields such as medical packaging and food preservation. For example, by combining dissolved PET with biodegradable biopolymers, a new material with both good mechanical properties of PET and biodegradability can be developed, which is expected to alleviate the pressure of plastic waste on the environment.

   In addition, dissolved PET can also be used to prepare materials with special structures and properties. By controlling the dissolution and solidification processes, PET materials with porous structures can be prepared, which have a high specific surface area and potential applications in adsorption, separation, catalysis, and other fields. For example, using the template method, dissolved PET solution is filled into a porous template, and then the template is removed to obtain a porous PET material with specific pore size and pore structure, which can be used for gas adsorption and separation.

2. New Thoughts on PET Recycling and Utilization

   The emergence of dissolution technology has brought a new direction for PET recycling, which has profound significance for PET recycling and also points out a new development direction for future recycling. The traditional PET recycling method is mainly mechanical recycling, which involves reprocessing waste PET into plastic products through steps such as crushing, cleaning, and melting. However, this method has many limitations. Mechanical recycling is difficult to remove impurities and additives from PET, resulting in a decrease in the quality and performance of recycled PET, and can only be used in some fields with lower performance requirements, such as the production of fillers, carpet fibers, etc. Moreover, mechanical recycling is not effective in handling complex mixed plastic waste and cannot achieve high-purity recycling.

   In contrast, dissolution technology can effectively overcome these problems. It uses selective solvents to separate PET from other impurities and polymers, achieving high-purity recovery. The dissolved PET solution can be purified to remove most impurities and obtain nearly pure PET material, which has similar properties to native PET and can meet the requirements of high-purity applications such as food grade packaging. For example, when dealing with mixed plastic waste, by adjusting the solvent formula, PET can be selectively dissolved while other plastics remain insoluble, thereby achieving effective separation of PET from other plastics and improving recycling efficiency and quality.

   From the perspective of future development direction, the integration of dissolution technology with other recycling technologies will be an important trend. On the one hand, dissolution technology can be combined with chemical recovery methods such as pyrolysis and depolymerization. Firstly, the main pollutants are removed through dissolution technology, and recyclable PET is purified. Then, chemical recycling technology is used to further degrade PET into basic chemical monomers or oligomers, achieving deep resource recovery and recycling. On the other hand, dissolution technology can also serve as a pretreatment step for mechanical recycling. For plastic waste that is difficult to separate mechanically, dissolution technology can be used to remove impurities that are difficult to remove by mechanical separation, which can significantly improve the purity and efficiency of the final recycled material.

   With the continuous advancement of technology, more environmentally friendly and efficient dissolution technologies and solvent systems may be developed in the future. For example, developing green solvents to reduce environmental impact; Explore new dissolution processes to reduce energy consumption and costs. At the same time, advanced technologies such as artificial intelligence and big data may also be applied in the field of PET recycling. Through intelligent monitoring and optimization of the recycling process, the efficiency and quality of recycling can be further improved, promoting the development of the PET recycling industry towards a more sustainable and efficient direction.

VII. Conclusion: Exploration Never Stops

The seemingly simple task of dissolving PET bottles actually contains rich scientific knowledge and practical value. We have gained a deep understanding of the chemical structure and physical properties of PET, understood the mysteries of its intermolecular interactions, and explored the possibility of dissolving it in various solvents. From the futile use of common organic solvents to the remarkable use of special solvents, we continue to explore and gradually find the key to unlocking the door to PET dissolution.

In the dissolution experiment, we rigorously carry out every step, from material preparation to precise control of experimental conditions, and every detail is crucial to the success or failure of the experiment. Through careful observation and analysis of experimental phenomena and results, we have come to a profound understanding of the critical impact of factors such as temperature, time, and solvent ratio on dissolution efficiency. These valuable experiences will provide a solid foundation for subsequent research and applications.

At the same time, we cannot ignore the importance of safety and environmental protection. Strict safety measures are the barrier to protect our health when using toxic and harmful solvents; The environmentally friendly treatment of dissolved products is our responsibility towards our home planet. Only under the premise of safety and environmental protection can PET dissolution technology achieve sustainable development.

Looking ahead, the technology of dissolving PET bottles has broad prospects in both scientific research and recycling industries. In the field of scientific research, it will inject new vitality into the innovative development of materials science, helping us develop more high-performance and multifunctional materials; In terms of recycling, it is expected to drive the PET recycling industry towards a more efficient and environmentally friendly direction, contributing to solving the problem of plastic waste pollution.

However, we are also aware that current dissolution technologies still have some shortcomings, such as solvent toxicity and high costs. This requires us, as researchers and practitioners in related industries, to continue to work hard and explore new solvent systems and dissolution methods, in order to improve dissolution efficiency and effectiveness while reducing environmental impact and costs. I hope more people can join this exploration team, let’s work together and write a more brilliant chapter for the development of PET dissolution technology.