The analysis of the low-temperature resistance performance of acrylic solid surfaces should be carried out from three dimensions: material structure, mechanical response and environmental interaction, and a comprehensive assessment should be conducted in combination with laboratory tests and actual application scenarios. The following analysis is carried out from three aspects: key performance indicators, test methods and failure mechanisms:
First, changes in physical properties in low-temperature environments
The influence of glass transition temperature (Tg)
The Tg of acrylic resin is usually between 0℃ and 50℃. When the ambient temperature is lower than Tg, the coating changes from a highly elastic state to a glassy state, and the molecular chain movement ability decreases significantly. For example, a coating with a Tg of 10℃ may have its flexibility reduced by more than 50% in an environment of -10℃, resulting in a decline in impact resistance.
Low-temperature embrittlement phenomenon
Brittle fracture may occur in the coating within the range of -30℃ to -50℃. It can be observed through the notch impact test that the coating with ductile fracture at room temperature transforms into brittle fracture at low temperature, and the cross-section shows a mirror-like feature, indicating that the crack propagation energy is significantly reduced.
Accumulation of contraction stress
Low temperature causes the volume of the coating to shrink. If the thermal expansion coefficient does not match that of the substrate, it may trigger interfacial stress. For example, the shrinkage rate difference between the coating and the metal substrate may reach 0.5% at -20℃, resulting in a decrease in adhesion or coating cracking.
Second, the testing method for low-temperature performance
Low-temperature embrittlement temperature test
In accordance with the GB/T 5470-2008 standard, the coating samples were placed in the fixture cooled by liquid nitrogen and cooled at a rate of 2℃/min. The temperature at which the coating broke was recorded. The embrittlement temperature of typical acrylic coatings is between -40℃ and -60℃. Below this temperature, the coating is prone to catastrophic damage.
Low-temperature bending test
After keeping the coated sample at -20℃, -40℃ and -60℃ for 2 hours, immediately conduct a 180° bending test. Observe whether there are cracks or peeling on the surface of the coating. For example, when the bending radius is less than 5mm at -40℃, the coating may develop microcracks at the 0.1mm level.
Low-temperature adhesion test
After being maintained at the set temperature for 30 minutes, the adhesion was evaluated by the grid method. For example, a coating with adhesion grade 0 at room temperature may drop to grade 2 at -30℃, indicating that low temperature leads to the weakening of interfacial bonding force.
Low-temperature cycling test
To simulate the temperature difference between day and night, the coating sample was subjected to 100 cold and hot cycles within the range of -40℃ to 20℃, with each cycle lasting for 2 hours. Observe whether the coating shows powdering, bubbling or peeling, and evaluate its long-term weather resistance.
Third, failure mechanisms in low-temperature environments
Cracking caused by internal stress
Low-temperature shrinkage causes tensile stress within the coating. When the stress exceeds the tensile strength of the coating, it may trigger cracks perpendicular to the surface. For example, a coating with a thickness of 100μm may produce radial cracks 0.2mm wide at -50℃.
Interface debonding
If the adhesion between the coating and the substrate is insufficient, low-temperature shrinkage may cause interface peeling. It can be observed through SEM that the cross-section of the coating treated at -30℃ shows obvious interlayer separation, and the residue at the interface is reduced.
Microphase separation intensifies
At low temperatures, the compatibility between the soft and hard segments in acrylic resin decreases, which may lead to microphase separation. For instance, copolymers with significant differences in Tg may exhibit phase separation structures at the 5-10μm level at -20 ° C, which affects the uniformity of the coating.
Fourth, verification of actual application scenarios
The exterior walls of buildings in extremely cold regions
In an environment of -40℃, the coating’s resistance to freeze-thaw cycles needs to be verified. For example, soak the coated sample in water and freeze it at -40℃, then transfer it to 20℃ for melting. Repeat this 50 times and observe whether the coating peels off.
Cold chain transportation equipment
For cold storage environments ranging from -25℃ to -18℃, it is necessary to test the corrosion resistance of the coating under low-temperature and high-humidity conditions. For example, after the coating is maintained at -20℃ and 90%RH for 72 hours, whether white frost or rust appears on the surface.
Coating of polar equipment
Under extremely cold conditions of -60℃, the impact resistance of the coating needs to be evaluated. For example, a drop hammer impact test was adopted. The coating was impacted at -60℃ with an energy of 1J, and it was recorded whether visible cracks occurred.
Fifth, performance optimization direction
Molecular structure design
The introduction of flexible segments (such as butyl acrylate) can reduce Tg and improve low-temperature toughness. For instance, copolymerizing ethyl acrylate with butyl acrylate can reduce the Tg from 20℃ to -10℃, significantly improving the low-temperature performance.
Crosslinking density regulation
Moderate crosslinking can enhance the strength of the coating, but excessive crosslinking will reduce its flexibility. For instance, by adjusting the dosage of the crosslinking agent, the low-temperature embrittlement temperature can be reduced by 10℃ while maintaining hardness.
Filler modification
Adding nanoscale fillers (such as fumed silica) can inhibit crack propagation. For example, adding 5% nano-fillers can increase the elongation at break of the coating by 20% at -40℃.
