The market for recycled polyethylene today is quite diverse. One just has to type in the Internet the query “Granule secondary” and you can get a large selection of companies involved in the processing of polyethylene. Processing companies offer a secondary granule of different grades, transparency, color and price range. In such a huge variety of offers to consumer companies, recycled polyethylene raw materials are not always easy to make a choice.

What should you pay attention to when buying a secondary pellet?

First of all, each manufacturer of plastic products has a number of technological requirements due to the peculiarities of the production of a particular product from polyethylene.

Key technologies for the production of polyethylene products include: extrusion, casting and blowing. Each of these technologies requires certain physical and mechanical properties of polyethylene raw materials. And if the properties of primary polyethylene are determined by GOSTs, then the situation with the secondary granule is not so clear.

What are the main physical and mechanical properties of recycled polyethylene that need attention?

1. The melt flow rate (MFR)

PTR is one of the most important properties of polyethylene. It shows how much the melt under a given pressure and temperature is squeezed out in a special capillary in 10 minutes. The more PTR, the secondary granule is more fluid and less viscous. For primary polyethylene, this indicator is determined by GOST. For the secondary – measurements in the laboratory. On average, this indicator for LDPE granules is 0.24-1.0 g / 10 min. For HDPE 0.1-0.6 g / 10 min.

2. Thermal conductivity

Polyethylene is easily modified when exposed to pressure and temperature. The production of products based on the property of thermal conductivity (for example, thermal insulation) will depend on the thermal conductivity of the main raw material (in our case, polyethylene). The coefficient of thermal conductivity of polyethylene is 0.36-0.43 W / m0K.

3. Specific gravity

The properties of polyethylene depend significantly on its specific gravity. In fact, this indicator determines its density. For the secondary granules of LDPE and HDPE, these indicators will differ. For LDPE, the average specific gravity is about 0.91 g / cm3, and for HDPE it is about 0.94 g / cm3.

4. Melting point

The basic composition of the secondary granule can be quickly determined by this indicator, since the melting temperature of LDPE and HDPE are significantly different. For the secondary granule of LDPE, this indicator will be in the range from 103 to 110 ° C, and for HDPE it is much higher – 130 to 137 ° C. It should be noted that pressure also significantly affects the melting temperature of polyethylene. Low melting point can significantly increase the performance of the extruder.

5. Calorific value

The calorific value of polyethylene is very important in the process of properly setting up process equipment and in particular the extruder. Without knowing this indicator, it is difficult to determine the optimal technological mode of production.
The range of calorific value of polyethylene, depending on the brand, is from 44.0 to 47.2 MJ / kg. Another important point is the use of polyethylene products as part of materials with increased fire safety requirements. In this case, the ignition temperature of the polyethylene, which is 306 ° C, must be taken into account.

The given indicators are the main ones when choosing the “right” secondary granule of polyethylene, and, accordingly, the “right” supplier.