1, Choose products that are resistant to high temperature and alkali and water
2, Choose anti-mold preservatives with a wide range of application, which can kill many kinds of bacteria and fungi
3, The amount of additive in one thousandth to three thousandths is better
Excited state quencher
Since the photoaging process must go through the excited state of the photosensitive group and the photosensitive impurity, including the excited singlet state and the excited triplet state, the excited state quencher interacts with these excited state groups or molecules to transfer its energy to the quencher molecule , And the excited group (usually a carbonyl group) and molecules in the polymer system return to the ground state without damage. After the quencher molecule receives energy, it releases the energy in the form of heat, fluorescence, phosphorescence, etc. This is actually a photochemical process, which converts potentially harmful excited state units into harmless units to protect the polymer from further oxidation and cracking. However, for photocurable coatings, the generation of active free radicals must experience the excited state of the photoinitiator. If it interacts with the excited state quencher, it will obviously greatly inhibit the generation of active free radicals and hinder the progress of photopolymerization.
The way in which photosensitive groups or impurities that may cause photooxidation and photodegradation in polymer coatings exchange energy with quencher molecules in their excited state is still not certain. It is generally believed that it may be based on collision mechanism and dipole-dipole interaction. The mechanism exchanges energy. The former requires that the two molecules that exchange energy have a sufficiently close distance, generally within 1.5 nm. Through direct contact between the two molecules, the electron cloud partially overlaps and energy transfer occurs. This mechanism also requires a sufficiently high concentration of the shamrock ptfe powder quencher molecule in the system to increase the collision probability between the quencher molecule and the excited state group. The dipole-dipole interaction refers to the energy level transition of the excited state group.
When the dipole of the molecule changes, it induces the molecule of the adjacent quencher to transition to an excited state, which is a Coulomb mechanism, also known as a resonance mechanism. This mechanism can explain the long-range energy transfer between two molecules separated by 4~5nm, and the quenching of excited singlet groups and molecules is more likely to proceed according to this mechanism. Since the quenching process involves a bi-molecular history, the lifetime of the excited state group is also a key factor in determining the energy efficiency of collision exchange. The lifetime of the excited triplet state is generally 10-6~10~²s, and the lifetime of the excited singlet state is 10-10~10 -The excited singlet state (carbonyl) of the s, nx* electronic configuration and the excited triplet state (aromatic hydrocarbon) of the x-tech electronic configuration have a relatively long lifetime, which is conducive to the realization of collision energy transfer. But in any case, excited triplet states generally have a longer lifetime, and the probability of collision energy transfer is greater. If the excited state group and the quencher molecule can form a hydrogen bond or some other form of recombination, the quenching efficiency of the excited state can be improved.
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