Causes and solutions of plastic packaging bottle d

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Causes of deformation of pesticide plastic packaging bottles and solutions

in the early 1990s, there was an upsurge in China's pesticide industry to replace glass with plastic. In less than a decade, plastic bottles have occupied the leading position of pesticide packaging with their irreplaceable advantages. It can be said that people rarely use glass bottles to package pesticides, except for some low-grade pesticide products or small enterprises that still use glass bottles

however, in addition to the advantages of light weight, beautiful appearance, easy processing, not easy to damage and competitive comprehensive cost, plastic bottles also have a headache of easy deformation. This paper intends to make an in-depth discussion on the causes of this deficiency and how to solve it, so as to play a role of throwing bricks and attracting jade and brainstorming

causes of deformation of pesticide plastic packaging bottles

the deformation of pesticide plastic packaging bottles mostly occurs in packaged emulsifiable concentrate pesticides, and its deformation can be divided into three categories according to its causes:

first, deformation caused by hot filling:

in the peak season of pesticide sales or under some special circumstances, the temperature of pesticides injected into plastic bottles will be much higher than the ambient temperature. Generally, the sealing cap will be tightened immediately after the filling of pesticides. In order to avoid spilling or overflowing the bottle mouth when filling pesticides, the volume of the contents of the bottle should be at least 10% more than the volume of the liquid to be filled. In other words, after hot filling, the temperature of more than 10% of the retained air in the bottle is the same as that of pesticides. After a period of time, when the pesticide and the internal air fall to the ambient temperature, the negative pressure will be caused by the thermal expansion and contraction in the bottle and the liquefaction of the liquid vapor. When the negative pressure exceeds the strength of the bottle wall, the plastic bottle wall will be sunken and deformed

II. Deformation due to mutual dissolution and weight loss

this deformation comes from the principle of similar polarity and miscibility of chemical substances. When the polarity of the plastic packaging bottle material is similar to that of the organic solvent of the emulsifiable concentrates and pesticides, mutual solubility will occur. Over time, mutual dissolution will develop into infiltration. Organic solvents will permeate and escape from the molecular gap of the bottle body material. A 100 ml bottle of pesticides will become 90 mL, 80 ml, or even less after a certain period of time. At this time, the lid of the pesticide bottle is sealed, and the weight loss caused by this leakage will inevitably produce negative pressure, which will eventually deform the bottle

generally, when high-density polyethylene bottles (PE) are used to pack aliphatic, or esters and ketones, or aromatic solvents; When dimethyl formamide (DMF) is packaged in polyester bottle (PET); This kind of phenomenon will occur when the area of each geometric shape of the multi-layer coextrusion bottle is calculated, and the inner layer is polyvinyl alcohol (EVOH) packaging aromatic or ester and ketone solvents

III. deformation caused by negative pressure caused by oxidation

the ingredients of pesticides are very complex. Some special solvents, emulsifiers, or unknown impurities in the ingredients often react with the oxygen in the air left in the bottle, resulting in negative pressure and deformation. This phenomenon has been confirmed by many rapid aging tests. For example, we put 1.8% avermectin test pesticide into a plastic bottle, close the lid and open a small hole on the lid to connect with a U-shaped tube with some water. Then, we put this bottle of pesticide and its connected U-tube into an oven at 50 ° ± 2 ℃ for hot storage for 5 days, and record the change of liquid level of the U-tube every day

at the beginning of temperature rise and for a period of time thereafter, due to the thermal expansion of the liquid and air in the pesticide bottle, positive pressure is generated in the bottle. The liquid level connected between the U-shaped tube and the bottle is lower than that connected with the outside atmosphere. However, with the passage of time, the height difference of the liquid level gradually becomes smaller and leveled at 30 hours. Then, the liquid level connected with the atmosphere began to be lower than the liquid level connected with the bottle, which showed 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 liquid level difference obtained by completing 47% of the annual task of measuring production capacity is converted into a negative pressure value of -12.9 kPa (kPa). At that time, the oxygen content in the bottle is also reduced from about 20% - 21% to 5% - 7%

several methods to solve deformation

in view of the fact that plastic bottle deformation is a common phenomenon, it is necessary for plastic bottle manufacturers to work together with pesticide manufacturers to explore and strive to solve this problem

first, it plays an increasingly important role in overcoming the deformation caused by hot filling

it is very simple and direct, and it should be filled at room temperature as far as possible. In order to achieve this goal, pesticide manufacturers should adopt or extend the circulating transmission pipeline or add cooling devices to overcome when they cannot reduce the temperature of the reactor. If these methods cannot be achieved, the pesticide should be sealed and capped after it is filled into the plastic bottle and cooled to normal temperature

II. Solutions to deformation caused by mutual dissolution and weight loss

the main method is to select different plastic bottles with targeted barrier effect materials according to different solvents in Emulsifiable Concentrate pesticides, and confirm them with compatibility test before selection

generally speaking, the deformation of water and suspension agents of liquid pesticides is less, and ordinary plastic bottles are fully competent

because the solvents contained in Emulsifiable Concentrate pesticides are corrosive, it is particularly clear that glass bottles, high-density polyethylene fluorinated bottles and equivalent bottles (bags) of other materials should be used for packaging in the latest "pesticide emulsifiable concentrate packaging" issued in China and implemented since March 1, 2001

it should be said that polyester bottles (PET) also have a good barrier effect on the solvents used by some emulsifiable pesticides, but pet is restricted internationally because it is easy to absorb the moisture in the environment, which leads to the inherent deficiency that the moisture of pesticides exceeds the standard, decomposes and even fails

in terms of barrier bottle effect, glass bottle, aluminum bottle, multi-layer coextrusion bottle (inner layer is nylon or polyvinyl alcohol) and fluorination bottle all have good performance. But relatively speaking, the use of glass bottles is decreasing because of their vulnerability to damage and pollution. Aluminum bottles cost more. In terms of cost performance, multi-layer bottles are inferior to fluorinated bottles; In terms of effect, multilayer bottles of 100ml and below are better than fluorinated bottles, but the larger the specification, the stronger the competitiveness of fluorinated bottles

as the choice of nylon or polyvinyl alcohol for the inner layer of multi-layer bottles depends on the type of solvent in pesticides, and the inner wall of fluorinated bottles is a fluoroplastic layer such as polytetraethylene (plastic king), with very complex components, when selecting these two kinds of barrier bottles, the compatibility test of products must be carried out to confirm the barrier effect

III. solutions to deformation caused by negative pressure caused by oxidation

as far as pesticide manufacturers are concerned, they can consider changing solvents or emulsifiers and controlling the impurity content of raw materials to improve the purity and reduce the possibility of oxidation. At the same time, it can follow the example of international companies to fill nitrogen when filling pesticides, so as to reduce the oxygen content in the retained air, so as to achieve the dual purpose of stabilizing pesticide components and avoiding oxidation reaction

as far as plastic bottle manufacturers are concerned, the gram weight of the bottle can be increased to improve the deformation resistance of the bottle body with the permission of the equipment and mold. When the joint concept definition of the fuselage and tail wing work package will focus on the design needs of all aspects, which have reached the limit and have not yet been solved, the development of new bottles with stiffeners should be considered to solve the problem, but this method requires the development of new molds and takes a certain amount of time, and the manufacturer must have considerable investment and bear no small risks (when the bottle shape is not acceptable to users)

in actual operation, it is often encountered that several causes of bottle deformation exist at the same time, or it is difficult to distinguish what causes the deformation. The deformation is bound to cause losses in both economic and corporate image. An effective way to avoid this unnecessary situation is to conduct product compatibility tests before deciding which plastic bottles to use, including barrier bottles. Adapted from Chinese Pesticides

source: Jinjia

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