Mechanical Grinding
Mechanical reduction process utilizes liquid nitrogen to pulverize heat-sensitive textile fibres into a fine powder for chemical analysis. Lowering the temperature below the glass transition point of the polymer prevents the material from melting or deforming during the grinding stage. Implementing cryo-milling ensures that the resulting sample maintains its original chemical composition without thermal degradation.
High-purity nitrogen provides the necessary cooling for processing elastic fibres that would otherwise resist mechanical shearing.
Thermal Mechanism
Cooling occurs within a closed chamber where the textile sample is submerged or sprayed with liquid nitrogen. During cryo-milling, the impact of a high-speed hammer or ball mill shatters the brittle material into uniform particles. Constant monitoring of the nitrogen levels prevents the sample from warming up and becoming gummy.
Sample Preparation
Processing duration and impact frequency are adjusted based on the denier and toughness of the yarn. Because cryo-milling produces a very high surface area, the subsequent solvent extraction becomes considerably more efficient. This method is preferred for difficult materials like aramid or high-tenacity nylon.
Physical Threshold
Particle size distribution depends on the duration of the mechanical impact and the initial size of the fabric swatch. If cryo-milling continues for too long, the energy from the impact may eventually overcome the cooling capacity. Fine powders obtained through this process allow for the detection of trace contaminants at parts per billion levels.
