Experiment § Shrinkage of thermosetting resin
The picture on the left shows the volume change of the thermosetting resin during curing. From unreacted liquid (point A) to curing into solid (point E). VA represents the initial volume at temperature T1; when the temperature is increased to T2, the volume expands to VB. It cures into solid at temperature T2 and shrinks to VC in volume. At this time, the resin is very soft, showing a rubbery state during the cooling process, and shrinks with a relatively large expansion coefficient α2. When the temperature drops to the Tg point (point D), the cured product turns into glass state and shrinks with a relatively small expansion coefficient α1. To organize the above discussion: S1: A→B, the liquid expands when heated; S2: B→C, liquid curing shrinkage; S3: C→E, solid cooling shrinkage; S4: B→E, the maximum shrinkage in the entire process; S5: A→E, total shrinkage. The shrinkage rate mentioned in the technical data usually refers to S5, that is, the volume change from liquid to solid; For many customers, they see the traces of liquid expansion at point B, so they feel that the resin shrinks significantly (S4). From the point of view of stress, we are more concerned about the resin characteristics of D→E: Because the material has greater rigidity in the glass state, shrinkage stress will occur at this position. Different needs have different concern. Which point should you focus on in your case?
─Author: Ming-Hsu, Li
Activity § Passionate July
The products made by Yunlin disadvantaged groups are the first choice for company gifts. Therefore, before Dragon Boat Festival, our company bought the meat dumplings made by Douliu GSWF for everyone. The proceeds from their charity sale will help vegetative and disadvantaged families. In July, we bought dumplings made by McMillan Social Welfare Foundation, which has the purpose of helping the disabled find employment. Plus, this dumpling workshop passed ISO22000 and HACCP certification, which shows their intentions. In addition to public welfare activities, summer interns are waiting for us to bring them a different experience. Because safety is very important, the factory has installed flammable gas detectors and regularly conducts fire drills for poisonous disasters. Everyone says that July this year is different from last year. As the weather gets hotter, we become more enthusiastic.
Knowledge § Difference between tin catalyst and non-tin catalyst
Due to stricter global regulations, tin catalysts (e.g. dibutyltin dilaurate) commonly used in moisture curing products tend to be converted to non-tin catalysts (e.g. Ti, Zn, Bi, Zr). From the perspective of catalysts, whether tin catalysts or non-tin catalysts, they all accelerate the overall reaction rate through the hydrolysis reaction and then the organic metal reaction with the resin. The difference between the two is that the basic properties of the different center metals are different, such as the radius, the degree of electronegativity, etc, which cause different reactivity. In the process of converting tin catalysts into non-tin catalysts, many difficulties will be encountered, such as insufficient reactivity, re-design of the formula, bad adhesion, large changes in colloidal viscosity, color changes, and so on. It's not as simple as switching directly.
Living § Trip in Africa (1)
Last year, the school arranged my family to entertain a 15-year-old teenager from Kenya. When he was about to leave Taiwan, I told him, "One day, I will definitely visit you in Africa." In June of this year, my daughter and I signed up for international volunteers and rushed to the mysterious country — Africa. Before we set off for Africa, we had to go to the hospital to administer Yellow Fever Vaccine and get malaria medicine. There are many aboriginal tribes in Africa so far, maintaining a primitive way of life, and the Maasai tribe is one of them. On the steppes of East Africa, Maasai, who live as nomads, sell handicrafts to increase their income. To this day, the tribes still do not use electricity, they use wood to make fire. They reject modern Western culture and adhere to the traditional way of living. They have polygamy and live in houses made of cow dung concrete. The house is 5~6 pings large but needs to accommodate 6~7 people. The Maasai welcome visitors with lively singing and dancing, accompanied by the "war dance" with a higher bounce ratio. This is a competitive game. If you jump higher, you can not only attract the favor of the opposite sex, but also gain respect. Before leaving, I saw the driver holding a box of leftover food to the Maasai. A swarm of adults and children rushed to get food. At this moment, I remembered the news that there was a report that the food leftover in western society was enough to feed and feed Africans. It's hard to imagine if you don't witness it with your own eyes, so we should cherish it.
─Author: Miao-Ling, Lin
