Low-melting polyesters are modified forms of polyesters with reduced melting points. It is achieved by incorporating modifying components during the traditional polyethylene terephthalate (PET) polymerization process.
So in simple, it can lower its melting point by changing its molecular structure. It is an environmentally friendly product. Used as a partial replacement for traditional adhesives. Its application fields include non-woven fabrics, filter materials, clothing adhesive linings, soundproof, mattresses, automotive interior materials, adhesive threads, insulation cotton, shoe materials, etc.
Over the years, the development of low-melting polyester has increased the product varieties. It also led to the expansion of application fields. In my country, low melting point polyester is mainly produced through copolymerization. The monomers involved include isophthalic acid (IPA), diethylene glycol (DEG), polyethylene glycol (PEG), etc.
Despite this, the China composite spinning market still relies on imports. So, it is important to accelerate the development of domestic industry. it can replace imported products and reduce production costs.
1）The Process of 110°C Low Melting Point Polyester
The process of creating 110°C low melting point polyester is primarily based on the synthesis of conventional PET, with the addition of third monomers like IPA, fourth monomers such as dicarboxylic acids, and fifth monomers, namely diols. This combination results in the production of 110°C low melting point polyester. Other components in the formulation include purified terephthalic acid (PTA), antimony-based catalysts, titanium-based catalysts, and cobalt acetate.
What is the suitable quantity of the fifth monomer, diols? As the quantity of diols gradually increases, the melting point decreases, and the color deteriorates. So, more diols do not necessarily yield better results. When both DEG and terminal carboxyl content are within standard units. That is, the mass fraction of DEG is <4% and COOH is <30mol/t. It is recommended to add 8%-12% glycol. Low melting point polyesters are modified forms of polyesters that have a reduced melting point. It is achieved by adding modifying ingredients during the traditional PET polymerization process.
2）Characteristics of low melting point polyester
1. The higher glass transition temperature
If we add IPA and dibasic acid into conventional low-melting point polyester, the melting point is lowered. But the glass transition temperature and softening point of polyester are significantly lowered. This effect is practicality. Lowering the melting point while increasing the softening point and glass transition temperature is a contradiction. The addition of modified monomer diols plays a crucial role in resolving this contradiction. The glycol structure contains two methyl groups. They increase the distance between the polymer chains in the polyester molecular structure. At the same time, they reduce intermolecular forces. So it increases the softening point and glass transition temperature. In this way, the conflict was successfully resolved.
2. Rheological Properties
Melts of low-melting polyesters (110°C) exhibit reduced shear thinning. This is a basic need for melt spinnability. The flow properties of 110°C low-melting polyester at 250°C are similar to those of conventional PET at 295°C. The viscosities of both types are comparable. So it is suitable for melt spinning.
3. Fiber Tensile Strength
The fiber tensile strength of 110°C low melting point polyester is 1.77 cN/dtex, with a breaking elongation of 94.97%. Due to the introduction of modified monomers, low melting point polyester reduces the regularity of molecular chains, leading to a decrease in fiber tensile strength. Notably, the breaking elongation of 110°C low melting point polyester significantly increases.
Data Sources: Partial information sourced from the Sinopec Shanghai Branch
3）Spinning Process of Low Melting Point Fibers
Low melting point polyester fiber, known as FDY (Fully Drawn Yarn), is a versatile material with various applications. Its production involves a series of steps. In this section, we will elaborate on the spinning process of FDY, which includes slicing, drying, melting, spinning, cooling, oiling, drawing, heat setting, re-oiling, and winding.
1. Slicing
The process begins with the creation of low-melting point polyester chips. These chips serve as the starting material for spinning FDY. They are typically obtained through the polymerization of PET. It is modified with specific monomers to achieve the desired low melting point.
2. Drying
Before further processing, it is essential to ensure that the chips are thoroughly dried. This step removes any moisture. It ensures a consistent quality of the material and prevents defects during the next stages.
3. Melting
The dried chips are then subjected to a melting process. During this stage, the chips are heated to their melting point, transitioning them from a solid to a molten state. This molten material will be the basis for creating the FDY.
4. Spinning
Once in a molten state, the material is ready for spinning. It is forced through spinnerets, which are essentially nozzles with tiny holes. As the material emerges from these openings, it solidifies into continuous filaments. These filaments are then wound onto bobbins.
5. Cooling
Immediate cooling is crucial to set the filaments in their current state. Cooling quenches the filaments. It preserves their physical properties and prevents them from sticking together.
6. Oiling
Oiling (First Pass): To enhance the handling and processing of the filaments, they are coated with a thin layer of lubricating oil. This coating reduces friction and static electricity, facilitating the subsequent processes.
7. Drawing
During the drawing process, the filament is elongated. It aligns the polymer chains and increases the tensile strength of the fiber. Other mechanical properties can also be improved. This stretching process significantly enhances the yarn’s performance.
8. Heat Setting
After drawing, the FDY is subjected to a heat-setting process. Heat setting involves heating the filament to a specific temperature. This allows any internal stress to be released. This step helps stabilize the fibers. and maintain their desired properties, including low melting point.
9. Oiling (Second Pass)
Following the heat setting, the FDY is once again coated with a layer of lubricating oil. This re-oiling ensures that the yarn remains smooth and pliable. It prevents any damage during winding and subsequent use of the material.
10. Winding
Finally, the FDY is wound onto spools or bobbins. These spools contain the finished low melting point polyester yarn. They are ready for distribution and utilization in various applications.
In summary, the spinning process of low-melting polyester FDY is a complex but well-structured sequence of steps. It starts with the fabrication of chips, through melting and spinning. It also includes critical stages such as stretching and heat setting. All this contributes to the production of versatile products. They are used in industries ranging from textiles, automotive applications, and to adaptable materials.
4）The Versatile Applications in Nonwoven Fabric
Low-melting-point PET fiber is a critical raw material in nonwoven fabric production. It accounts for 28% of nonwoven fiber applications (according to the European Nonwovens Association). Here explores the diverse applications and advantages of this material in various industries.
1. Characteristics of PET Nonwoven Fabric
1.1. Water-Repellent
PET nonwoven fabric is inherently water-repellent. Its resistance to water depends on its weight. Heavier fabrics exhibit superior water repellency, causing water droplets to roll off the surface.
1.2. High-Temperature Resistance
PET’s melting point is around 260°C, making it ideal for applications requiring temperature resistance. It maintains dimensional stability under high-temperature conditions. It is widely used in heat transfer printing, transmission oil filtration, and high-temperature-resistant composite materials.
1.3. Strength and Durability
PET nonwoven fabric is considered one of the best continuous filament nonwoven. It is second only to nylon filament nonwoven fabric. It offers excellent tensile strength, breathability, tear resistance, and aging resistance. It is suitable for various applications.
1.4. Gamma Radiation Resistance
PET nonwoven fabric possesses a unique characteristic – resistance to gamma radiation. This feature is especially valuable in medical applications. As it allows sterilization by gamma radiation. It does not affect the physical properties and dimensional stability of the fabric at the same time. This is a property that polypropylene (PP) nonwovens do not have.
2. Wide Range of PET Nonwoven Fabric Applications
The versatility characteristics of PET non-woven fabric are widely used. This can be seen through its wide range of applications in different fields:
2.1. Home Textiles
Used for anti-pilling linings, heat transfer printing, nonwoven calendars, office document bags, curtains, vacuum cleaner bags, and disposable garbage bags.
2.2. Packaging
Employed in cable wrap cloths, tote bags, container bags, flower packaging materials, desiccants, adsorbent packaging materials, and more.
2.3. Decoration
Used in wall decoration fabrics, floor leather base fabrics, plush base fabrics, and other decorative applications.
2.4. Agriculture
Applications include agricultural harvest fabrics, crop and plant protection materials, weed protection belts, and fruit-bearing bags.
2.5. Waterproof Materials
High-quality breathable (moisture-proof) waterproof materials are crafted from PET nonwoven fabric.
2.6. Industrial Applications
This material serves as a filtration material, insulation material, electrical material, and reinforcement material in various industrial contexts.
2.7. Others
Finds applications in protective gear, travel products, and more.
5）Packaging Details
Low-melting-point PET fibers are typically packaged inside woven polypropylene bags lined with polyethylene plastic bags. The standard packaging specifications are as follows:
Dimensions: ф1225 x 1240mm
Net Weight: 1000 ± 20 kg
6）Storage and Safety
It is essential to store PET fibers in well-ventilated, dry warehouses, separating them by batch and grade. The warehouse should be equipped with fire-fighting facilities.
Safety Precautions:
- When we store and transport, it is better to keep away from open flames and heat sources.
- Avoid mixing with chemical substances such as oil, acids, and alkalis.
- Take precautions during loading and unloading to prevent package damage and personal injury.
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