Low melting point polyester is a modified polyester with a lower melting point. By adding modifying components during the regular PET polymerization process, we change its molecular structure. This reduces the polymer’s crystallization ability, lowering its melting point. Low melting point polyester can partly replace traditional adhesives. It is a green and eco-friendly product. It is mainly used in non-woven fabrics, filters, garment linings, sofa fabrics, mattresses, automotive interiors, bonding threads, insulating wadding, and shoe uppers. In recent years, more products have been developed, and their applications have expanded.
1. Production of Low Melting Point Polyester Chips in HanLink Polyester
In China, low melting point polyester is mainly produced through copolymerization. Common modifying monomers include isophthalic acid (IPA), diethylene glycol (DEG), and polyethylene glycol (PET).
1.1 First Generation
HanLink Polyester developed the first-generation 110°C low melting point polyester. They added IPA and a fourth monomer (a dicarboxylic acid) during the regular PET synthesis. This achieved a 110°C melting point. However, this polyester had low glass transition and softening temperatures. It will cause sticking problems over time. These issues made production, transport, and use difficult.
1.2 Improvement to the Second Generation
HanLink polyester improved the formula to create a second-generation product. They added a fifth monomer, NPG, to reduce stickiness. Tests on the melting point, crystallization, rheology, and tensile strength ensured that the new formula met the technical requirements of spinning users.
2. Experiment
2.1 Materials
| Name | Specification | Source |
| PTA | Fiber grade | Sinopec |
| EG | Polymer grade | Sinopec |
| IPA | Industrial grade | Sinopec |
| Dicarboxylic acid | Industrial grade | Market |
| NPG | Industrial grade | Market |
| Antimony catalyst | Industrial grade | Market |
| Titanium catalyst | Industrial grade | Market |
2.2 Equipment and Instruments
- 10L stainless steel polycondensation reactor with electric heating, stirring, and automatic control systems.
- Labscan XE spectrophotometer (Hunterlab, USA).
- 848 automatic titrator (Metrohm, Switzerland).
- GC-14C gas chromatograph (Shimadzu, Japan).
- DSC821 differential scanning calorimeter (Mettler Toledo, Switzerland).
- RH7-2X capillary rheometer (Rosand, UK).
- XQ-1A fiber strength and elongation tester.
2.3 Analysis and Testing
We measured the viscosity of the polyester chips with an automatic viscometer, their color (b and L values) with a spectrophotometer, carboxyl end group content with an automatic titrator, DEG mass fraction with a gas chromatograph, and melting and crystallization properties with a differential scanning calorimeter. We tested the tensile strength and elongation of fibers according to GB/T14190-2008 standards.
We will also test whether its parameters meet the national standards of Chinese PET Chips.
2.4 Experimental Procedure
In the 10L apparatus, we used the original formula of low melting point polyester. In the esterification reactor, we added PTA, IPA, dicarboxylic acid, catalysts, and the fifth monomer NPG. We varied the NPG content at 5%, 8%, 15%, and 20%. We measured the melting point, intrinsic viscosity, carboxyl end group content, L value, b value, and DEG mass fraction of the different samples to ensure the chips met the required 110°C melting point and other quality standards.
We have written an article to introduce the parameter importance, kindly click here.
3. Results and Discussion
3.1 Effect of NPG on Melting Point
| Sample | Composition (%) | Melting Point (°C) | Intrinsic Viscosity (dL/g) |
| #1 | 100 PTA, 95 EG, 5 NPG | 202 | 0.74 |
| #2 | 100 PTA, 92 EG, 8 NPG | 180 | 0.76 |
| #3 | 100 PTA, 85 EG, 15 NPG | 150 | 0.77 |
| #4 | 100 PTA, 80 EG, 20 NPG | 110 | 0.79 |
As shown in the table, increasing the NPG content lowers the copolyester melting point. This occurs because NPG’s structure introduces two non-polar side methyl groups, increasing the distance between molecules and reducing intermolecular forces. Also, random copolymerization disrupts chain regularity, decreasing crystallization ability and completeness, thus lowering the melting point.
3.2 Analysis of 110°C Low Melting Point Polyester Chips Using DSC
We tested the 110°C low melting point polyester using differential scanning calorimetry (DSC). The test conditions were a temperature range from 30°C to 280°C and a heating rate of 20K/min. In the DSC test graph, we see a clear glass transition peak. However, the crystallization peak and melting peak are not clear.
3.3 Reasons for the Observations
During the polymerization process of the low melting point polyester, we added other chemical monomers. These additions disrupted the regular structure of the polyester molecules. This disruption reduced the crystallization ability. Under the same test conditions, the crystallization and melting processes became unclear. Thus, in the DSC spectrum of the 110°C low melting point polyester, we do not see clear crystallization and melting peaks.
4. Conclusion
As we increase the amount of each modifying component, the melting point of the copolyester decreases linearly. The addition of NPG, AA, and IPA disrupts the regularity of the polyester. This slows down the crystallization speed. Under experimental conditions, the crystallinity is very low and hard to distinguish in DSC analysis. However, samples treated with boiling water show clear crystallization.
This study shows that modifying agents can significantly affect the thermal properties of low melting point polyester. By understanding these effects, we can better control the properties of polyester for various applications.
