What environmental conditions should be considered during the storage of recycled polyester staple fibers to prevent deterioration? ​

Recycled polyester staple fiberDue to the characteristics of residual raw materials (such as trace impurities and high end group activity) and wide molecular weight distribution, the storage process is more sensitive to environmental conditions. If the environment is not properly controlled, it is easy to cause deterioration problems such as moisture absorption, clumping, yellowing aging, strength reduction, and mold growth. It is necessary to focus on controlling the following 6 types of environmental conditions and combine protective measures to ensure product quality:

1、 Temperature and humidity control: core anti moisture absorption and thermal aging

Although the moisture absorption of recycled polyester staple fibers is lower than that of natural fibers, the molecular chain end groups (such as carboxyl and hydroxyl groups) have higher activity and may contain trace hydrophilic impurities (such as detergent residues and dye additives) in the recycled raw materials, which can easily adsorb moisture from the air, leading to fiber clumping, "breakage" and "flying flowers" during subsequent processing, and even the growth of microorganisms. Meanwhile, high temperature accelerates the thermal degradation of molecular chains and reduces fiber strength.

Temperature requirement: The storage environment temperature should be stably controlled at 15-25 ℃, and the temperature difference between day and night should not exceed 5 ℃. Avoid getting close to heat sources such as heating pipes, boilers, and ventilation openings. If the ambient temperature exceeds 30 ℃, molecular chains are prone to thermal oxidation degradation, leading to yellowing of fibers and a decrease in fracture strength (experimental data shows that for every 10 ℃ increase in temperature, the thermal aging rate increases by 1-2 times).

Humidity requirement: The relative humidity should be maintained between 40% and 60%. If the humidity is greater than 65%, the moisture absorption of fibers will significantly increase (the moisture absorption rate of recycled polyester can reach 0.5% -0.8%, higher than that of native polyester by 0.4%), which is prone to "clumping and agglomeration", and water will accelerate the hydrolysis reaction of end groups; If the humidity is less than 35%, the fibers are prone to static electricity, adsorbing dust and impurities, which affects the quality of subsequent spinning.

Protective measures: Equipped with temperature and humidity sensors for real-time monitoring. Dehumidifiers should be placed in the warehouse in humid areas (such as the southern rainy season), and humidifiers can be used appropriately in dry areas; The warehouse walls and floors should be treated with moisture-proof measures (such as laying waterproof rolls and applying moisture-proof coatings to the walls) to prevent the bottom fibers from absorbing moisture due to moisture regain on the floor.

2、 Light protection: prevent aging and deterioration caused by ultraviolet rays

Recycled polyester staple fiberTrace amounts of unsaturated groups (such as aldehyde and ketone groups) may remain in the molecular chains of the recycled materials, and the dyes and additives in the recovered raw materials may have "photosensitivity", which can easily lead to photooxidation degradation under ultraviolet irradiation: molecular chain breakage, generation of chromophore groups, resulting in yellowing and brittleness of the fibers, and a significant decrease in strength (long-term exposure to sunlight may cause a 10% -15% decrease in breaking strength within one month).

Lighting requirements: The storage warehouse should avoid direct natural light, especially for south facing windows with strong ultraviolet rays. Light blocking curtains (such as thick canvas and sunscreen film) should be installed; If artificial lighting is used, it is necessary to choose LED lamps or incandescent lamps without ultraviolet rays, and avoid using mercury lamps and fluorescent lamps (including ultraviolet bands).

Additional protection: Fibers need to be sealed with * * opaque packaging materials * * (such as kraft paper bags lined with PE film or black plastic woven bags) to avoid direct contact with light caused by individual packaging damage; If there are gaps on the top and walls of the warehouse, they should be repaired in a timely manner to prevent rainwater leakage from being accompanied by direct sunlight.

3、 Space environment: prevention of impurity pollution and gas corrosion

The surface adsorption of recycled polyester staple fibers is strong (due to uneven molecular chains, the surface is prone to forming "uneven charge areas"). If there is dust, oil stains, or harmful gases in the storage environment, they can easily adhere to the fiber surface or penetrate into the packaging, causing pollution and deterioration; Meanwhile, certain gases may undergo chemical reactions with fibers, disrupting their molecular structure.

Impurity control: The warehouse should be kept clean and dust-free, and the floor should be regularly cleaned with a vacuum cleaner or wet mop (to avoid dust generated by dry sweeping). It is prohibited to stack other debris (such as engine oil, chemicals, food) in the warehouse to prevent oil leakage or insect and rodent attraction; Before storing fibers, the integrity of the packaging needs to be checked. If the packaging is damaged, it needs to be replaced with a new one before storage to avoid impurities from adhering during transportation.

Gas protection: Warehouses should be kept away from areas such as chemical plants, printing and dyeing factories that may emit harmful gases (such as sulfur dioxide, chlorine gas, acidic vapors). These gases can react with carboxyl and hydroxyl groups at the fiber end groups, leading to acidic degradation of the fibers; The warehouse needs to maintain good ventilation, but the ventilation openings need to be equipped with filters (such as 50 mesh dust-proof nets) to prevent external dust and pollutants from entering with the airflow. The recommended ventilation frequency is 1-2 times a day for 30 minutes each time (reduce ventilation in humid weather).

4、 Stacking method: anti extrusion deformation and local moisture

Recycled polyester staple fibers are usually stored in "bags" (25kg/bag or 50kg/bag). Improper stacking can cause the bottom fibers to be compressed for a long time, resulting in deformation and clumping, and excessive stacking can hinder air circulation, leading to local temperature and humidity rise, and causing mold or aging.

Stacking height: According to the packaging strength, the stacking height should be controlled between 4-6 layers (taking 25kg/bag as an example, not exceeding 6 layers); 50kg/bag with no more than 4 layers), to avoid bottom packaging breakage or fiber compression. If using pallets for stacking, it is necessary to choose plastic pallets with a load-bearing capacity of ≥ 500kg (to avoid moisture, mold, and fiber contamination of wooden pallets), with a reserved spacing of 20-30cm between pallets for air circulation.

Stacking spacing: The distance between the fiber pile and the warehouse walls and columns should be ≥ 50cm, and the distance from the ground should be ≥ 15cm (moisture-proof pallets or wooden frames can be placed), to prevent the wall from returning moisture and the ground from directly contacting the fibers; Recycled polyester staple fibers of different batches and specifications should be stacked in different zones with clear markings (such as production batch and purpose) to avoid confusion in subsequent use caused by mixing, and also reduce the risk of cross contamination.

Taboo stacking: It is prohibited to stack fibers at the entrance of the warehouse, under windows (easily affected by rainwater and light), or near fire-fighting equipment or power switches (to avoid accidental collisions that may cause packaging damage).

5、 Pest and microbial control: prevention of decay and mold

Recycled polyester staple fibers are not easily susceptible to insect infestation, but if the recycled raw materials contain natural fiber impurities (such as cotton and wool residues in blended fabrics), or if the storage environment is humid and there are food residues, it is easy to attract pests (such as moths and mites); At the same time, in high humidity environments, impurities on the surface of fibers (such as starch additives) can breed fungi (such as Aspergillus and Penicillium), causing the fibers to develop mold spots, odors, and even leading to molecular chain degradation.

Pest control: The warehouse conducts regular (once a month) pest inspections, with a focus on identifying hidden areas such as corners, pallet bottoms, and stacking gaps; Non toxic insect repellents (such as camphor balls and diatomaceous earth insect repellent powder) can be placed in the corners of the warehouse, but they need to be wrapped in breathable cloth bags to avoid direct contact with fibers (to prevent insect repellent components from penetrating and contaminating); Prohibit eating in the warehouse, clean up garbage in a timely manner, and cut off the source of food for pests.

Mold prevention and control: In addition to controlling humidity, desiccants (such as silica gel desiccants, calcium chloride desiccants, with 100g desiccants per 50kg of fibers) can be placed in the fiber pile. The desiccants need to be replaced regularly (their color darkens after being damp); If slight mold spots are found on local fibers, the batch of products should be immediately isolated and transferred to a well ventilated and dry place to air dry (avoid direct sunlight, cool ventilation can be used), and the surrounding fibers should be checked for contamination. Severely moldy fibers should be directly scrapped to prevent the spread of mold.

6、 Storage cycle and regular inspection: prevent long-term aging

Recycled polyester staple fiberThe storage period should not be too long, as even if the environment is controllable, the molecular chains will slowly undergo "thermal oxidative aging" during long-term storage, leading to a gradual decline in performance.

Storage period: It is recommended that the period from production completion to use should not exceed 6 months. If long-term storage (exceeding 6 months) is required, a monthly inspection should be conducted, focusing on checking the fiber color (whether it turns yellow), hand feel (whether it becomes brittle), and packaging integrity (whether it is damaged or hygroscopic);

Inspection method: Randomly select fiber samples from different stacking positions and test their fracture strength (compared with the initial data, if the decrease exceeds 8%, it should be used quickly) and moisture content (tested by drying method, if the moisture content exceeds 1%, dehumidification should be strengthened) to ensure that the product has not deteriorated.

Summary: Core Protection Logic

The storage and protection of recycled polyester staple fibers should revolve around two core principles: "inhibiting molecular chain degradation" and "preventing external pollution": slowing down end group hydrolysis and photo oxidation through temperature, humidity, and light control; Prevent impurities and insect contamination through space management and stacking methods; Timely detect signs of deterioration through regular inspections. Compared to native polyester staple fibers, recycled polyester is more sensitive to the environment due to residual raw materials and molecular structure characteristics, requiring more refined storage control to ensure performance stability during subsequent processing and use.