Reasons for Deformation of Pesticide Plastic Packaging Bottles and Solutions

In the early 1990s, there was a boom in the Chinese pesticide industry to replace glass with plastic. In less than ten years, plastic bottles have occupied the dominant position of pesticide packaging due to their irreplaceable advantages. It can be said that, except for some low-grade pesticide products or small businesses still using glass bottles, people rarely use it to package pesticides. However, in addition to the advantages of light weight, beautiful appearance, easy processing, not easy to break, and competitive overall cost, plastic bottles also have the disadvantage of being easily deformed. This article intends to make an in-depth discussion on the causes of this problem and how to solve it, and plays a role in attracting ideas and brainstorming. The deformation of pesticide plastic packaging bottles mostly occurs in the packaging of emulsifiable concentrate pesticides, and the deformation can be divided into three categories according to their causes: 1. Deformation caused by hot filling In the peak season of pesticide sales or in some special cases, the pesticides poured into plastic bottles temperature will be much higher than the ambient temperature. In general, pesticides will be sealed immediately after filling. In order to avoid splashing or overflowing the bottle mouth when the pesticide is filled, the inner volume of the bottle is generally at least 10% more than the volume of the liquid that needs to be filled. That is to say, the temperature of more than 10% of the trapped air in the bottle after hot filling is the same as that of the pesticide. When the pesticide and the internal air drop to the ambient temperature after a period of time, negative pressure will be caused in the bottle due to thermal expansion and contraction and the liquefaction of the steam on the liquid. When the negative pressure exceeds the strength of the bottle wall, it will cause the plastic bottle wall to sink and deform. 2. Deformation due to mutual dissolution and weightlessness. This deformation originates from the principle of similarity in polarity of chemical substances. When the polarity of the plastic packaging bottle material is similar to the polarity of the organic solvent of the emulsifiable concentrate pesticide packaged, mutual solubility will occur. Over time, miscibility develops into osmosis. The organic solvent will permeate and escape from the molecular gap of the bottle body material. A 100ml bottle of pesticides will become 90ml, 80ml, or even less after some time. Therefore, when the lid of the pesticide bottle is sealed, the weight loss caused by this leakage will inevitably generate negative pressure, which will eventually deform the bottle. Generally, when high-density polyethylene bottles (PE) are used to package aliphatic, or esters and ketones, or aromatic solvents; when polyester bottles (PET) are used to package dimethylformamide (DMF); when more This phenomenon occurs when the inner layer of the co-extruded bottle is polyvinyl alcohol (EVOH) packaging aromatic or ester and ketone solvents. 3. Deformation caused by negative pressure caused by oxidation. The composition of pesticides is very complex. Some special solvents, or emulsifiers, or unknown impurities in the raw materials are often oxidized with the oxygen in the air left in the bottle, resulting in negative pressure. deformed. We have done many rapid aging tests to confirm this phenomenon. For example, we put the 1.8% Abamectin test pesticide into a plastic bottle, close the lid tightly and make a small hole in the lid to connect it to a U-shaped tube with some water. Then, we put this bottle of pesticide and the U-shaped tube connected to it into 50°±Heat storage in an oven at 2 °C for 5 days, while recording the change of the liquid level of the U-shaped tube every day. At the beginning of the temperature rise and for a period of time after that, due to the expansion of the liquid and air in the pesticide bottle, a positive pressure is generated in the bottle. The liquid level in the U-shaped tube communicated with the bottle is lower than the liquid level in communication with the outside atmosphere. However, with the passage of time, the liquid level difference gradually became smaller, and it was flush at 30 hours. Then, the liquid level communicating with the atmosphere began to be lower than the liquid level communicating with the bottle, which indicated that negative pressure had begun to appear in the bottle. When the test pesticide is taken out and returned to room temperature after five days, the measured liquid level difference is converted into negative pressure value of -12.9 kPa (Kpa). 21% dropped to 5%~7%. Several methods to solve the deformation In view of the deformation of plastic bottles is a common phenomenon, it is necessary for plastic bottle manufacturers to work together with pesticide manufacturers to discuss and work hard to solve this problem. 1. The method to overcome the deformation caused by hot filling. It's simple and straightforward, filling at room temperature as much as possible. In order to achieve this purpose, pesticide manufacturers should adopt or extend the circulating transmission pipeline or increase the cooling device to overcome the inability to reduce the temperature of the reactor. If none of these methods can be achieved, the pesticides should be filled into plastic bottles and then sealed and capped when they are cooled to room temperature. Second, the solution to the deformation caused by mutual dissolution and weightlessness. The main method is to select plastic bottles with different targeted barrier effect materials according to different solvents in EC pesticides, and confirm them by compatibility test before selection. Generally speaking, liquid pesticides and suspensions are less deformed, and ordinary plastic bottles are fully capable. Because of the corrosive nature of the solvents contained in EC pesticides, glass bottles, high-density polyethylene fluorinated bottles and high-density polyethylene fluoride bottles should be used in the 'Pesticide EC Packaging', which was recently promulgated in my country and has been implemented since March 1, 2001. Equivalent bottles (bags) of other materials are used for packaging.