Evaluating The Quality of Thermal Barrier Strips Through DSC Melting Peak Temperature

  The energy efficiency and structural safety of thermally broken aluminum windows and doors depend critically on the quality of the PA66 thermal barrier strip base material. The market is flooded with products of varying quality, including those made from recycled or blended materials that cannot be distinguished by appearance or dimensions alone. The melting peak temperature in DSC (Differential Scanning Calorimetry) testing is widely recognized as a reliable, tamper-proof indicator for accurately assessing the purity of the base material and the stability of the formulation in thermal barrier strips. This article provides an in-depth overview of DSC melting peak temperature from the perspectives of testing principles, peak shape and temperature interpretation, characteristic spectral patterns of inferior products, and practical application significance, serving as a reference for product selection and quality control in the industry.

  

 1、What is the Detection of DSC Melting Peak Temperature for Insulation Strips

  Polyamide polymer materials have fixed melting and crystallization characteristics. There are significant differences in the melting temperatures of different grades, types, virgin materials, and recycled materials. DSC detection precisely controls the temperature and records the heat flow changes of the insulation strip sample during heating, generating a unique melting curve. The temperature corresponding to the highest point of the curve is the melting peak temperature.

  This detection method requires no complex sample preparation, has a short testing cycle, and offers high repeatability. Moreover, the peak temperature characteristics cannot be artificially manipulated through additives, coloring, or modification. It is currently the most reliable technical method for window profile manufacturers, testing institutions, and engineering parties to identify the material of insulation strips. A qualified PA66 insulation strip has a unique and fixed melting fingerprint, while blended or recycled materials show clearly identifiable abnormal patterns.

2、DSC Melt Peak Temperature and Peak Shape Characteristics of Compliant PA66 Insulation Strips

 Compliant building-grade PA66GF25 insulation strips exhibit two typical DSC features:

（1）A stable melt peak temperature within 260–265 °C, with minimal fluctuation and strong consistency within and across batches.

（2）A sharp, single, independent peak without shoulders or splitting, a flat baseline, and a narrow melting range, indicating a single resin component, regular molecular structure, and uniform crystallinity.

 This standard thermogram reflects the use of virgin polymerized PA66 resin, uniform glass fiber dispersion, no impurities or recycled materials, and a stable formulation system. The resulting thermal stability, mechanical properties, and weatherability fully meet national standards and the requirements for use in system windows and doors.

3、Typical Abnormalities in DSC Melt Peak Temperature of Substandard Insulation Strips

（1）Overall low melt peak temperature

Peak temperature below 260 °C, mostly due to the addition of PA6, recycled polyamides, or crushed waste plastics. The material experiences a lowered heat resistance threshold, making it prone to softening, creep, and shrinkage under high-temperature conditions. This leads to increased clearance between the insulation strip and aluminum profile, resulting in air/water leakage, reduced thermal performance of windows and doors, and long-term deformation or cracking.

（2）Double or multiple melt peaks

The presence of two or more distinct melt peaks in the DSC curve indicates mixing of different plastics with varying melting points, commonly seen in blends of PA66 with PA6, general-purpose plastics, or multiple types of recycled materials. Poor compatibility between components and inconsistent thermal expansion/contraction coefficients generate sustained internal stress under seasonal temperature variations, significantly accelerating aging and brittle fracture.

（3）Broadened or flattened melt peak with no sharp maximum

Typically caused by multiple high-temperature processing cycles of recycled materials, leading to molecular chain scission and disrupted crystallinity. The material undergoes substantial degradation in overall rigidity, heat resistance, and fatigue performance. Although it may appear similar to compliant products, the intrinsic properties no longer meet standards.

（4）Baseline drift and disordered melting range

Often attributed to excessive additives, fillers of varying types, or high levels of impurities in the raw material. These result in an uneven internal structure and extremely poor stability, making the product unsuitable for use in engineering applications or high-rise building windows and doors.

4、Key Factors Affecting the Stability of DSC Melt Peak Temperature in Insulation Strips

 Raw Material Purity: Virgin PA66 exhibits a constant melt peak temperature. Once recycled materials or other grades of polyamide are introduced, the peak temperature shifts immediately.

 Extrusion Processing Conditions: Excessive processing temperatures or high screw shear can cause thermal degradation of PA66, resulting in a slight decrease in peak temperature and broadening of the peak shape.

 Formulation System: Improper addition of glass fiber content, compatibilizers, antioxidants, or other additives can interfere with crystallization behavior, leading to distortion of the melt peak shape.

 Storage and Aging: Insulation strips exposed to prolonged sunlight, moisture, or aging undergo oxidative degradation of the molecular structure, which may also cause a minor shift in the peak temperature.

5、Significance of Promoting DSC Melt Peak Temperature Testing in the Industry

 First, it overcomes the misconception of appearance-based fraud. Substandard insulation strips can closely mimic the color, surface finish, and cross-sectional dimensions of virgin material products, but they cannot falsify DSC melt peak temperature characteristics—effectively eliminating the possibility of passing off inferior products as compliant ones through technical means.

 Second, it establishes a unified quality assessment criterion. Adopting DSC melt peak temperature as a mandatory inspection indicator for incoming goods, warehouse acceptance, and project submissions enables standardized determination of product compliance and simplifies the quality control process.

 Third, it enhances the safety level of window systems. Using genuine PA66 insulation strips with qualified melt peak temperatures ensures superior resistance to high temperatures, deformation, and aging for the entire window assembly, making it suitable for demanding applications such as high-rise buildings, coastal areas, and environments with large temperature fluctuations.

 Fourth, it guides healthy competition in the industry. By setting thermal performance indicators as a benchmark, manufacturers are incentivized to adhere to virgin material formulations and abandon the low-price competition driven by recycled content, thereby promoting the standardization and high-quality development of the insulation strip industry.