Can Alcohol be Stored in PET Bottles?

During the COVID-19 epidemic, alcohol has become a must-have for every household. Whether it is 75% medical alcohol or higher concentration industrial alcohol, they all play an important role in the battlefield of disinfection and sterilization. However, in the process of using alcohol, a common scenario may raise questions: when the alcohol at home is used up and there happens to be an empty bottle of PET that has just finished drinking, can the newly opened alcohol be poured in for temporary storage? Alternatively, some people, for convenience, simply pack large barrels of alcohol into PET bottles and leave them in a corner of their home. This seemingly ordinary action hides a lot of scientific knowledge and safety hazards behind it. Perhaps you would say that you have done this many times without any problems. But is it really like this? Can alcohol and PET bottles coexist peacefully? Are the risks of short-term storage and long-term storage the same? These seemingly minor issues are related to our health and family safety. Today, let’s delve into this topic and see if it’s safe or not to store alcohol in PET bottles during cohabitation.

I. Basic Characteristics of Alcohol

Alcohol, chemically known as ethanol, is a common organic compound. In daily life, we come into contact with a wide variety of alcohol types, which can be divided into medical alcohol, industrial alcohol, and edible alcohol according to their uses.

Medical alcohol is the most familiar type, typically with a concentration of 75%, which has the best bactericidal effect. It can quickly penetrate the cell membrane of bacteria, causing protein coagulation and denaturation, thereby achieving the goal of killing bacteria. In addition to the 75% concentration, there is also 95% medical alcohol, which is generally used for disinfecting the surface of medical equipment or diluted in some cases before use.

The purity of industrial alcohol is usually high, reaching over 95%, but it may contain harmful substances such as methanol. Methanol is toxic and can cause serious harm to the human body, even endangering life, when consumed. Therefore, industrial alcohol should never be used for human disinfection or consumption.

Edible alcohol is used in the food processing and brewing industries, and its purity and hygiene standards are strictly regulated to ensure that it does not pose a threat to human health.

In terms of chemical properties, alcohol is a good organic solvent, which is an important characteristic of it. It can dissolve many organic substances, such as oils, resins, certain plastic components, etc. This characteristic is also the key to exploring whether alcohol can be stored in PET bottles, because as an organic solvent, alcohol may interact with the material of PET bottles.

In addition, alcohol also has the characteristics of high volatility and flammability. Alcohol has a low boiling point and is easily volatile into gas at room temperature. When the concentration of alcohol in the air reaches a certain range, it will ignite or even explode when exposed to an open flame. This is also an important reason why we need to pay special attention to safety when storing and using alcohol.

II. Unveiling the Material of PET Bottles

PET, The chemical name is polyethylene terephthalate, which is a common polymer material. It is made by the condensation reaction of terephthalic acid and ethylene glycol.

Structurally, PET molecular chains contain ester groups, which give PET many excellent properties. Firstly, PET has excellent mechanical properties, high strength, good toughness, and can withstand certain pressure and impact forces, which is also one of the reasons why it is widely used in the production of beverage bottles. Bottles made of PET are not easily broken, making them convenient for transportation and carrying.

Secondly, PET has good barrier properties and has a certain barrier effect on gases such as oxygen and carbon dioxide, which helps to maintain the freshness and taste of beverages. At the same time, it also has good water barrier properties, which can prevent liquid leakage inside the bottle.

In addition, PET has high transparency, making the bottles crystal clear and easy for consumers to observe the liquid inside, which is a great advantage in beverage packaging. Moreover, PET material is easy to process and shape, and can be used to produce bottles of various shapes and specifications through processes such as blow molding, meeting different packaging needs.

In addition to its widespread application in the field of beverage packaging, PET is also used in the production of food packaging, textiles, films, and more. In terms of food packaging, packaging materials made of PET can ensure the safety of food because they comply with relevant food contact material standards.

However, PET materials also have their limitations. Its heat resistance is relatively poor. Generally speaking, PET bottles may deform when the temperature exceeds 60 ℃. Moreover, under the action of certain chemicals, the structure of PET may be affected, leading to changes in its properties. We will elaborate on this point later when discussing the interaction between alcohol and PET bottles.

III. Chemical Reaction Between Alcohol and PET Bottles

1. Theoretical Compatibility Analysis

   From the perspective of chemical structure, there is a certain interaction between the ester groups in PET molecular chains and alcohol (ethanol) molecules. The ester group is a polar group, and ethanol molecules contain hydroxyl (- OH) groups, which are also polar groups. According to the principle of ‘similar solubility’, there may be some solubility between polar molecules.

   However, PET is a crystalline polymer material with a relatively regular arrangement of molecular chains and high crystallinity. This regular structure makes the interaction force between PET molecules strong, and the binding between molecular chains is relatively tight, which to some extent hinders the penetration and dissolution of ethanol molecules.

   In addition, the molecular volume of ethanol is relatively small, but the gaps between the molecular chains of PET are small, which makes it difficult for ethanol molecules to enter the internal structure of PET. Therefore, under normal conditions, such as room temperature, low concentration of alcohol, and short-term exposure, PET has a certain tolerance to ethanol, and the two are not prone to violent chemical reactions.

   From the perspective of chemical thermodynamics, the reaction between PET and ethanol requires a certain amount of energy to break the chemical bonds between PET molecular chains. In the absence of external energy input (such as high temperature, high pressure, etc.), the likelihood of this reaction occurring is low. So theoretically, under normal conditions, alcohol and PET bottles can temporarily coexist peacefully.

2. Performance in Actual Situations

   Although PET theoretically has a certain tolerance to alcohol, in practical situations, various factors can affect the interaction between the two, leading to some changes in PET bottles.

   Firstly, the impact of high concentration alcohol. Experiments have shown that when the alcohol concentration reaches over 95%, the surface of PET bottles may experience slight swelling when stored at room temperature for a long time. This is because high concentrations of alcohol have stronger solubility and can slowly penetrate between the molecular chains of PET, disrupting the forces between PET molecules and causing a certain degree of structural change in PET.

   Secondly, there is the influence of temperature. In high temperature environments, such as in cars or places with direct sunlight in summer, the temperature may exceed 60 ℃, and the problem of insufficient heat resistance of PET bottles will become apparent. At the same time, high temperature increases the speed of molecular motion, enhancing the activity of alcohol molecules and making it easier for them to interact with PET molecules. There was an experiment where PET bottles containing 95% alcohol were placed in an environment of 40 ℃. After one month, it was found that the hardness of the PET bottles decreased, the bottle walls showed slight thinning, and trace amounts of PET degradation products were detected in the alcohol.

   In addition, storage time is also an important factor. Even under normal temperature and low to medium concentration alcohol conditions, long-term storage may cause changes in the performance of PET bottles. Researchers have conducted an experiment where 75% medical alcohol was placed in PET bottles and left at room temperature for 6 months. As a result, it was found that the weight of PET bottles had decreased, indicating that some PET material had been dissolved by alcohol. At the same time, alcohol was tested and found to contain trace amounts of substances such as diethyl terephthalate, which are products of PET degradation.

   There are also some practical cases that can illustrate the problem. A user reported that after putting industrial alcohol (with a concentration of 99%) into PET beverage bottles and leaving them in the garage for a month, they found that the bottles had become slightly soft and the bottle mouth had leaked. After opening the bottle, you can still smell a faint odor, which is likely caused by the partial dissolution of PET in alcohol.

   In addition, the manufacturing process of PET bottles can also affect their interaction with alcohol. Some low-quality PET bottles have poor chemical corrosion resistance due to improper process control, irregular molecular chain structure, low crystallinity, and are more prone to problems when in contact with alcohol. For example, some recycled PET bottles may experience a decline in material properties after multiple processing steps, and may experience faster swelling, deformation, and other phenomena when storing alcohol.

IV. The Risks and Hazards of Storing Alcohol in PET Bottles

1. Health Risks

   When PET bottles swell and degrade under the action of alcohol, some components in the PET material may dissolve into the alcohol, posing health risks.

   During the synthesis process of PET, a small amount of monomers such as terephthalic acid and ethylene glycol may remain. If these monomers dissolve in alcohol and are exposed or ingested by the human body, they can pose a health hazard. Terephthalic acid has a certain degree of irritation to the respiratory tract and skin of the human body, and long-term exposure may cause symptoms such as respiratory inflammation and skin allergies. Ethylene glycol has a certain degree of toxicity. After ingestion, it will be metabolized in the body to produce oxalic acid, which will combine with calcium ions to form calcium oxalate stones, affecting kidney function.

   In addition, some additives such as plasticizers and stabilizers may be added to PET bottles during the production process. The main function of plasticizers is to increase the flexibility of PET, but some plasticizers (such as phthalates) have endocrine disrupting effects, and long-term exposure may affect the human endocrine system, especially the growth and development of children, which may have adverse effects. When PET bottles come into contact with alcohol, these additives may dissolve out and enter the alcohol.

   If we use alcohol containing these impurities for skin disinfection, the impurities may be absorbed into the human body through the skin; If used to wipe the surface of objects, especially tableware, toys, etc., these impurities may indirectly enter the human body. Although the intake may be relatively small in the short term, long-term accumulation can pose a potential threat to human health.

   Studies have shown that individuals who use alcohol stored in PET bottles for long-term hand disinfection have slightly higher levels of phthalates in their blood compared to the normal population. Although this research result cannot directly prove that it is caused by additives in PET bottles, it also sounds an alarm for us.

2. Safety Risks

   Alcohol is a flammable liquid with a low flash point, with 75% of medical grade alcohol having a flash point of approximately 22 ℃. It is highly susceptible to combustion when exposed to open flames, static electricity, and other conditions. The characteristics of PET bottles may increase the safety risks of alcohol storage.

   Firstly, the sealing of PET bottles may be affected by the action of alcohol. As mentioned earlier, alcohol may cause swelling and deformation of the PET bottle mouth, resulting in a decrease in the sealing performance of the bottle mouth. Alcohol has strong volatility, and poor sealing can cause alcohol to evaporate into the air, increasing the concentration of alcohol in the air. When the alcohol concentration in the air reaches 3% -19%, an explosion will occur when encountering a fire source, which undoubtedly poses a great risk to home safety.

   Secondly, PET bottles have poor heat resistance and are prone to deformation and softening in high-temperature environments. If PET bottles containing alcohol are placed near a fire source or exposed to direct sunlight for a long time, the temperature inside the bottle will increase, the evaporation rate of alcohol will accelerate, and the pressure inside the bottle will increase, which may cause the bottle to break and alcohol to leak out. Leaking alcohol can trigger a fire when exposed to an open flame.

   In addition, PET bottles are prone to breakage when subjected to impact or compression. If PET bottles containing alcohol accidentally fall off or are squeezed, the risk of fire can also increase if the alcohol flows out after the bottle ruptures. Especially in some public places such as laboratories, factories, etc., a large amount of alcohol packaged in PET bottles is stored. Once an accident occurs, the consequences can be unimaginable.

   Another easily overlooked safety risk is static electricity. In a dry environment, friction between PET bottles and alcohol may generate static electricity, and alcohol vapor is flammable. Sparks generated by static electricity may ignite alcohol vapor, causing combustion or explosion.

V. Suggestions for Selecting Containers for Storing Alcohol-Suitable Container for Storing Alcohol

1. Glass bottle: Glass bottles are one of the ideal choices for storing alcohol. The chemical stability of glass is very good, and its main component is silicon dioxide, which has stable chemical properties and is not easily reacted with alcohol. Whether it is high or low concentration alcohol, storing it in a glass bottle will not cause the components of the glass to dissolve into the alcohol, ensuring the purity of the alcohol.

   Moreover, the sealing of glass bottles can be done very well. Using glass bottles with rubber stoppers or screw caps can effectively prevent alcohol evaporation. Meanwhile, glass bottles have good heat resistance and can withstand high temperatures, making them less prone to deformation or breakage even in high-temperature environments during summer.

   However, glass bottles also have the disadvantage of being fragile. Extra caution is required during use and transportation to avoid collisions. But overall, for long-term storage of alcohol, glass bottles are the preferred choice.

2. Special plastic bottle: The special plastic bottle referred to here refers to a plastic container that meets the alcohol storage standards, usually made of polyethylene (PE) or polypropylene (PP) material.

   Polyethylene (PE) material has good chemical stability, strong resistance to organic solvents, and is not easily dissolved by alcohol. PE plastic bottles have a soft texture, good flexibility, strong impact resistance, and are not easily broken, making them suitable for packaging and carrying alcohol.

   Polypropylene (PP) material has better heat resistance than PE and can maintain stability at temperatures above 100 ℃. Meanwhile, PP material also has good chemical corrosion resistance and will not undergo significant chemical reactions when in contact with alcohol. PP plastic bottles have moderate hardness and good sealing, making them an excellent choice for storing alcohol.

   These specialized plastic bottles strictly follow the relevant packaging standards for food contact materials and chemical reagents during the production process to ensure their safety. When purchasing, we can choose specialized plastic bottles labeled with words such as ‘can store alcohol’ and ‘resistant to organic solvents’.

3. Metal containers: For large amounts of alcohol used in some industries, metal containers such as aluminum or stainless steel containers can be considered for storage.

   A dense oxide film will form on the surface of aluminum containers, which can prevent chemical reactions between aluminum and alcohol, thereby ensuring the stability of alcohol. Aluminum containers are lightweight, strong, and easy to transport and store.

   Stainless steel containers have better corrosion resistance and strength, can withstand higher pressures and temperatures, and are suitable for long-term storage of large amounts of alcohol. However, it should be noted that food grade or industrial grade stainless steel containers should be selected to avoid using inferior stainless steel containers to prevent metal ions from dissolving into alcohol.

VI. Reasons for not Recommending Long-Term Storage of PET Bottles

Based on the previous analysis, we can summarize several main reasons why it is not recommended to use PET bottles for long-term storage of alcohol.

Firstly, from the perspective of chemical stability, although PET bottles may not undergo significant reactions with alcohol in the short term, alcohol will slowly cause swelling and degradation of PET during long-term storage. Especially in high concentration alcohol and high temperature environments, this effect will be more pronounced, leading to a decrease in the performance of PET bottles, deformation, leakage and other problems.

Secondly, from the perspective of health risks, PET bottles may release harmful substances such as residual monomers and additives under the action of alcohol. These substances dissolve into alcohol and pose a potential threat to human health. Long term use of such alcohol for disinfection or skin contact may cause a range of health problems.

Again, in terms of safety risks, the sealing of PET bottles may decrease during long-term storage of alcohol, leading to alcohol evaporation and increasing the risk of fire and explosion. Moreover, PET bottles have poor heat resistance and impact resistance, and are prone to rupture when exposed to high temperatures, impacts, and other conditions, causing alcohol leakage and leading to safety accidents.

In addition, the original design intention of PET bottles is for storing low corrosive liquids such as beverages, not for storing organic solvents such as alcohol. The sealing structure of the bottle mouth and the strength of the bottle body cannot meet the requirements for long-term storage of alcohol.

So, in order to ensure the quality of alcohol, safety of use, and our health, it is not recommended to store alcohol in PET bottles for a long time. Even for short-term storage, attention should be paid to storage conditions, such as avoiding high temperatures, direct sunlight, and using up as soon as possible.

VII. Other Key Points for Storing Alcohol-Environmental Condition

1. Cool and ventilated: The environment where alcohol is stored must be kept cool and ventilated because alcohol has strong volatility. A cool environment can reduce the evaporation rate of alcohol and decrease the concentration of alcohol vapor in the air. Ventilation can timely discharge the evaporated alcohol vapor, avoiding its accumulation in local spaces and reducing the risk of fire and explosion.

   The ideal storage location can be a cool cabinet, basement, etc., where the temperature is relatively low and the air can circulate. Avoid storing alcohol in high temperature areas such as kitchens and boiler rooms, and do not place it in enclosed spaces such as wardrobes and drawers.

2. Keep away from sources of fire and high temperatures: Alcohol is a flammable substance and must be stored away from sources of fire such as lighters, gas stoves, candles, etc. At the same time, avoid contact with high-temperature objects such as heaters, electric heaters, ovens, etc.

   Experiments have shown that alcohol is highly prone to combustion and even explosion when exposed to open flames. The high temperature environment can accelerate the evaporation rate of alcohol, and may also cause the container storing alcohol to deform due to heat, increasing the risk of leakage. Therefore, the temperature of the place where alcohol is stored should not exceed 30 ℃.

3. Avoid direct sunlight: Direct sunlight can raise the temperature of the environment where alcohol is stored, and the ultraviolet rays in sunlight may have a certain impact on the alcohol and storage container. For glass containers, direct sunlight may cause an increase in temperature inside the bottle, while for plastic containers, ultraviolet radiation may accelerate their aging and reduce their performance.

   So, when storing alcohol, choose a place away from light or use opaque containers to prevent direct sunlight.

VIII. Daily Usage Precautions

1. Sealed storage: Regardless of which container is used to store alcohol, ensure good sealing. After each use, the lid should be tightly closed to prevent alcohol from evaporating. For glass bottles, check if the bottle stopper is tight; For plastic bottles, make sure the cap is tightened to avoid loosening. If there is a problem with the sealing of the container, it should be replaced in a timely manner to avoid waste and safety hazards caused by alcohol evaporation.

2. Avoid contact with children: Alcohol is toxic and flammable, and children have a strong curiosity. Once they come into contact with alcohol, they may accidentally drink it or cause danger while playing. Therefore, alcohol must be stored out of reach of children, such as high cabinets, lockable cabinets, etc. At the same time, safety education should be provided to children, informing them of the dangers of alcohol and advising them not to touch it casually.

3. Keep away from open flames during use: When using alcohol for disinfection and other operations, it is necessary to keep away from open flames. Do not use alcohol in places with fire sources such as the kitchen, and do not smoke while using alcohol. After using alcohol, wait for the alcohol to completely evaporate before carrying out operations with open flames. If disinfecting the surface of an object, use a clean cloth dipped in alcohol to wipe it, and do not directly spray alcohol near an open flame.

4. Reasonable packaging: If it is necessary to package large barrels of alcohol, suitable containers should be selected, such as the specialized plastic or glass bottles mentioned earlier. When packaging, be careful not to fill it too full. Generally, it should be filled to about 80% of the container to prevent alcohol from expanding and overflowing when the temperature changes. The packaged alcohol should be labeled with the alcohol concentration and storage date for easy management and use.

5. Regular inspection: For stored alcohol, regular inspections should be conducted to check whether the container is damaged or leaking