Recycling and granulation process of waste plastic

Waste plastic recycling granulation is a recycling method that turns waste plastic into granules through a granulation process. Regenerated granules can be used for molding processing, and the performance of the obtained product is similar to that of the original product, which has high economic value. Compared with landfill and incineration of waste plastics, recycled granulation is a true recycling of resources.

The quality of recycled plastic particles and the performance of recycled plastic products depend on the granulation process. Finding a simple, convenient, fast, efficient, energy-saving, environmentally friendly, economical and applicable process is the focus of research in the field of plastic granulation.

1. Meltless granulation

The process flow of meltless granulation is shown in the figure below.

The non-melting granulation process first cleans and screens the waste plastics to remove metal and other impurities, then crushes the waste plastics and sends them to the compressor by the pneumatic system, and makes the materials into strips through the compression and twisting action of the compression system

(This process is below the softening point of plastic Vicat and completed in a very short time),

Then the strip material is cooled and pulverized, the particle size of the material is controlled to be 4-8mm, and the fine powder is separated and sent to the compression system for re-granulation.

The large particle materials and impurities such as metals are separated again to remove impurities such as metals, and the particles with qualified sizes are packaged for storage or used for molding processing.

This process does not require an external heat source, the compression time can be precisely controlled, and the processing temperature is lower than the Vicat softening point of the plastic to avoid thermal degradation of the material.

However, the control accuracy of the size of plastic particles in the crushing link is not high, the size of the obtained particles is uneven, fine powder is easily produced, and the granulation efficiency is low.

2. Wet granulation

The wet granulation process is: collection→sorting→crushing→cleaning→drying→melting→granulating. There are various types of waste plastics collected, with dust, sand, oil stains, etc. attached to the surface. These impurities seriously affect the quality of recycled plastics. Generally, these impurities are removed by increasing the frequency of crushing and cleaning, so as to improve the quality of recycled products, and then extruded through an extruder, and finally the molten plastic is cut into uniform particles of appropriate size. Collection and sorting are done manually, crushing, cleaning, and drying are done by crusher, cleaning device, and dryer. Plastic melting is carried out in a screw extruder. The molten plastic is extruded through a die and granulated by a pelletizing device. .

Wet granulation is a commonly used granulation method, and its advantages are simple process, low cost and wide application of products;

The disadvantage is that crushing, cleaning, drying, extrusion and pelletizing all require special equipment, the production cost is high, the working noise is loud, dust and sewage are easily generated, and secondary pollution is caused.

3. Dry granulation

The technological process of dry granulation is: collection→crushing→separation and impurity removal→melting→granulation. Dry granulation eliminates the cleaning and drying process, and increases the separation and removal of impurities. Separation methods are divided into floating-sink separation, flotation separation, electro-selection separation, near-infrared spectrum separation, etc.

Compared with wet granulation, dry granulation saves the cleaning and drying process and saves water resources, especially in places where water resources are seriously scarce.

However, since the quality of the product depends on whether the impurity removal is thorough, it is necessary to install special impurity removal equipment to remove impurities, which increases the production cost.

4. New granulation process

(1) Organic solvent assisted softening and granulation.

The organic solvent assisted softening and granulation process is based on the traditional extrusion process by adding an organic solvent softening process to help the plastic soften quickly. At the same time, the organic solvent can also protect the internal molecular structure of the plastic from damage and ensure the quality of recycled plastics.

Its process is: Firstly, the waste plastics are sorted and broken into flake materials, washed with water and then dried to control the moisture content of the materials to 1% to 4%.

The material is aggregated into particles with a diameter of 0.3-2 cm and a bulk density of 600-1000 kg/m3 through an agglomerator; Secondly, put waste plastics, heavy calcium carbonate and organic solvent antimony trichloride into the granulator, stir and mix evenly and carry out catalytic reaction to obtain composite materials and the composite material is transported to a screw-type electric melting machine for heating to become thick; Finally, the softened waste plastic is extruded through an extrusion device to obtain recycled plastic, and the recycled plastic is cut into pellets by a pelletizing device.

(2) Composite regeneration granulation.

At present, most recycled plastics are a mixture of various plastics, which have complex components, low strength, poor processability, and dull color. Therefore, recycled plastics are mostly used in low-end plastic products, without the inherent characteristics of plastics. In response to this problem, a preparation method of composite recycled plastics was proposed. Compared with the existing technology, this process restores the good transparency, heat resistance and processing stability of recycled plastics through the compounding of inorganic powder and waste plastics, with the help of the transparency, heat resistance and fluidity of inorganic powder , making recycled plastics more widely used and reducing the cost of recycled plastics. The process is as follows: firstly, the inorganic powder and abrasive are mixed by a high-speed mixer at 120-140°C to obtain a uniformly mixed slurry; Next, add the uniformly mixed slurry into a grinder to grind it into powder, and add plasticizer and waste plastic to a double-rotor continuous mixer for mixing, so that the inorganic powder is embedded in the completely plasticized waste plastic to form homogeneous body; Finally, the obtained homogeneous body is directly fed into the extrusion granulation equipment, and composite recycled plastic granules are obtained through extrusion, pelletizing, and cooling.

(3) Hot air circulation heating, melting and granulation.

Hot air circulation heating melting granulation is a brand-new technology in the extrusion granulation process. It uses hot air circulation to heat waste plastics to melt the plastics and then extrude them for granulation. Compared with the traditional melting granulation process, it directly heats waste plastics, which saves the process of crushing, cleaning, drying, etc., improves the working environment, saves investment costs, and avoids secondary pollution. It has broad application prospects.

The equipment used in the hot air melting granulation process is a vertical hot air circulation heating waste plastic recycling granulator. The structure diagram of the vertical hot air circulation heating waste plastic recycling granulation experimental prototype is shown in the figure below.

The main structure includes hopper, stirring shaft, stirring plate, screen, feeding screw, heating plate, centrifugal fan, motor, heating pipe, etc.

The working principle is: the material is fed from the hopper and falls into the box, heated by hot air circulation, accelerated to melt under the action of the stirring shaft, and extruded to granulate through the screw, and at the same time, under the action of the centrifugal fan, the hot air passes through the centrifugal fan and the heating tube in turn. Then enter the box, so that the reciprocating cycle completes the heating. However, there are some problems in the vertical experimental prototype, such as unreasonable size and structure, and lack of pelletizing device; The stirring shaft and the screw are coaxial, and the speed of the stirring shaft and the screw cannot be adjusted separately; the extrusion die is close to the ground, which causes difficulties for subsequent pelletizing.

In view of the existing problems of the vertical hot air circulation granulator, the vertical type can be changed into a horizontal type, so as to solve the difficulty of vertical granulation and the coaxial problems of the stirring shaft and the screw. Its structural diagram is shown in the figure below.

The main structure includes hopper, stirring shaft, stirring plate, screen, screw, centrifugal fan, heating pipe, etc.

The working principle is: the material is fed from the hopper, falls on the screen, is heated by hot air circulation, accelerates melting under the action of the stirring shaft and falls to the screw. Through screw extrusion and granulation, at the same time, under the action of the centrifugal fan, the hot air passes through the screen, the centrifugal fan, the heating pipe in turn, and then enters the box, so that the reciprocating cycle completes the heating.

Nanjing Haisi Extrusion supply plastic recycle machine line for PET BOTTLES/ PP PE FILMS with washing and crushing machine.

Any interest please feel free to contact us!