Wisdom For Polyethylene vol.30
30. Correct Material Analysis of Polyethylene Bags
2025-12-04
Visual inspection alone is insufficient for polyethylene identification
When examining a polyethylene bag requested for quotation, it may look like an ordinary bag, but its actual characteristics must be considered.
Simply assuming “transparent = LDPE or LLDPE, semi-transparent and crisp = HDPE” is not always reliable.
For daily-use or trash bags, rough identification may be sufficient. However, in chemical, pharmaceutical, or electronic device packaging, strict property requirements and performance standards necessitate detailed analysis. A bag that appears to be a single-layer film may in fact be multilayered.
Five analytical methods used for polyethylene materials
(1) Differential Scanning Calorimetry (DSC)
DSC is the first method performed for material estimation. The melting point differs depending on the material, allowing approximate identification.
For example, LDPE and HDPE each have characteristic melting point ranges. Multiple melting points may indicate a blended or multilayer film. DSC can also distinguish between low- and high-melting LDPE, providing information on heat resistance and heat-sealing properties.
DSC is the first method performed for material estimation. The melting point differs depending on the material, allowing approximate identification.
For example, LDPE and HDPE each have characteristic melting point ranges. Multiple melting points may indicate a blended or multilayer film. DSC can also distinguish between low- and high-melting LDPE, providing information on heat resistance and heat-sealing properties.
(2) Fourier-Transform Infrared Spectroscopy (FT-IR)
To improve identification accuracy, FT-IR analysis is conducted. Infrared light is irradiated onto the sample, and transmission/reflection characteristics are measured to identify molecular structure. Combining DSC and FT-IR results enables more precise material identification.
To improve identification accuracy, FT-IR analysis is conducted. Infrared light is irradiated onto the sample, and transmission/reflection characteristics are measured to identify molecular structure. Combining DSC and FT-IR results enables more precise material identification.
(3) Gas Chromatography (GC) for Organic Additives
Organic additives are analyzed using GC. Samples are vaporized at high temperature, components separated, and substances identified and quantified. By comparing additive peaks, types and concentrations of antioxidants (phosphite, phenolic) and lubricants can be determined.
Organic additives are analyzed using GC. Samples are vaporized at high temperature, components separated, and substances identified and quantified. By comparing additive peaks, types and concentrations of antioxidants (phosphite, phenolic) and lubricants can be determined.
(4) Ashing and ICP Analysis for Inorganic Additives
Inorganic additives (such as AB agents or silica) are analyzed via ashing. The sample is combusted at high temperature, and the remaining ash is analyzed for composition.
ICP (Inductively Coupled Plasma Spectroscopy) measures elemental content. In semiconductor-related applications, ion chromatography (IC) or ICP-MS is used to measure cations, anions, and trace metal impurities.
Inorganic additives (such as AB agents or silica) are analyzed via ashing. The sample is combusted at high temperature, and the remaining ash is analyzed for composition.
ICP (Inductively Coupled Plasma Spectroscopy) measures elemental content. In semiconductor-related applications, ion chromatography (IC) or ICP-MS is used to measure cations, anions, and trace metal impurities.
(5) Microscopic Analysis for Multilayer Structure
Cross-sectional microscopy is used to confirm whether the film is single- or multilayered. This allows measurement of layer thickness and detailed structural observation, enabling comprehensive evaluation of material properties.
Cross-sectional microscopy is used to confirm whether the film is single- or multilayered. This allows measurement of layer thickness and detailed structural observation, enabling comprehensive evaluation of material properties.
Conclusion
Even polyethylene that appears simple may have complex material characteristics. Accurate analysis according to application requirements is essential for proper material selection.
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