Recycling of PP woven bags

1 Introduction With the widespread use of "" plastic woven bags (hereinafter referred to as "" bags "), the production volume of" "bags has become larger and larger, and more and more such waste bags have followed. Recycling these waste bags for recycling is an effective measure to reduce production costs, protect the environment, and make full use of resources. In recent years, many manufacturers have conducted research in this regard.
What is discussed here is the recycling of "" bags. Waste refers to "" plastic waste products suitable for the production of "" bags. This is a single kind of waste utilization, which requires relatively high requirements. It cannot be mixed with other kinds of plastics, and it must not contain sediment, debris, mechanical impurities, etc., and its melt index is required to be in the range of 2-5 pp plastic is available). There are two main sources of it, one is the waste in the production process of "bags"; the other is the recycled products of waste pp bags, such as fertilizer bags, feed bags, salt bags, etc.
2 Regeneration methods It mainly has two kinds of melting granulation method and extrusion granulation method, most of which use extrusion granulation method. The flow of the two methods is as follows.
2.1 Molten pellet method Waste material-material selection and washing-drying-cutting-high-speed pellets (feeding-heat shrinkage-water spray-pellets) out of the packaging.

2.2 Extrusion granulation method Waste-selection of materials-washing-drying-cutting-heating extrusion-cooling and cutting-packaging.
The equipment used in the extrusion method is a self-made two-stage extruder. In order to exclude the gas generated in the waste extrusion, a vented extruder can also be used. In order to eliminate the debris in the waste, 80-120 mesh screen must be used at the discharge end of the extruder. The process conditions for regeneration extrusion are shown in Table 1.

The temperature of the extruder should be properly controlled, not too high or too low. If the temperature is too high, it may cause aging and yellowing of the material, or even carbonization and blackening, which will seriously affect the strength and appearance of the plastic. If the temperature is too low, the plasticization will be poor, the extrusion rate will be low, and even the material will not be discharged. It is particularly easy to damage the filter. The appropriate regenerative extrusion temperature shall be determined later based on the results of sampling and testing the melt index of each batch of recycled waste. The temperature conditions in Table 1 are the general rules based on production practice experience.

3. The use of recycled materials and the impact on the performance of pp bags due to heat aging during plastic processing has a considerable impact on the performance, especially the recycled "" bags have undergone two or even multiple heat processes, plus the use before recycling The UV aging, the performance has decreased significantly. The test data of Table # 1 can illustrate this point.

It can be seen that the recycling of "" bags cannot be used repeatedly indefinitely. If pp bags are produced using recycled materials alone, they can only be recycled up to three times. Since the recovered waste is difficult to judge the number of times it is recycled, therefore, to ensure the quality of the pp bag,
Even the less demanding bags should be mixed with new materials and recycled materials in production. The proportion of the mixture should be determined based on the measured data of the two materials. The amount of recycled materials directly affects the quality of pp bags and flat yarn. The table is a set of comparative data in production practice.

The key to the quality of the woven bag is the relative tensile strength and elongation of the flat yarn. The strength of the flat yarn specified by the national standard (gb8946--88) is> = 0.03N / denier, and the elongation is 15%-30 .% Therefore, in production, generally add 40% of recycled materials. Depending on the quality of the reclaimed material, sometimes 50%-60% can be added. The more the amount of recycled material added, although the production cost is lower, but the quality of the bag can not be guaranteed, therefore, the amount of recycled material can only be added appropriately under the premise of ensuring quality.

4. The use of recycled materials to adjust the drawing process. Due to multiple thermal processing of pp plastics, thermal aging and ultraviolet radiation aging in long-term use have caused the melting index of pp recycled materials to increase with the number of processing times (see Table 2) . Therefore, after adding a large amount of recycled materials to the new material, the temperature of the extruder, the head temperature, and the stretching and setting temperature should be adjusted appropriately lower for the control of the process temperature, and the adjustment amount should pass the test. The melt index of the mixture is determined.
On the other hand, because the recycled materials are processed many times, the molecular weight is reduced, a large number of short molecular chains exist, and they are stretched and oriented many times. Therefore, in the production process, the stretching ratio should be lower than that of the same new material. Generally, the draw ratio of brand-new materials is 4--5 times, and it is generally 3--4 times after adding 40% recycled materials. Also due to the increase in the melt index of the recycled material, the viscosity has been reduced, and the extrusion rate has been increased, so under the same screw speed and temperature conditions, the drawing speed of the wire drawing should be slightly accelerated. In the compounding of new and old raw materials, it is worth noting that they should be mixed evenly; at the same time

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