Recycling of polypropylene scraps in production” 

Recycling of polypropylene scraps in production: waste as a source of profit

In our practice of working with large extrusion lines, we have repeatedly encountered a situation where workshops for the production of pipes or sheet metal lost up to 18% of their margins simply due to ineffective disposal of process waste.Recycling of polypropylene scraps in productionis not just an environmental measure, but a strict economic necessity for a modern plant in 2026. The direct answer to the main question: yes, returning your own scraps (in-house production) to the extruder allows you to reduce the cost per kilogram of finished products by 35-42% compared to using only primary raw materials, subject to strict temperature conditions and granulation rules.

Many production managers mistakenly believe that it is enough to simply crush the sprues and launchers and pour them back into the hopper. This is a fundamental error that leads to degradation of the molecular weight of the polymer, the appearance of fish eyes on the surface of the product and, in the worst case, clogging of filters and stopping the line. In this article, we will analyze the full processing cycle, based on real cases from our clients from Russia and the CIS countries, where the implementation of a closed cycle made it possible to pay for crushing and granulation equipment in 4–6 months.

Technological features and physical and chemical properties of PP

Polypropylene (PP) is one of the most sensitive polymers to thermal-oxidative destruction among those widely used in industry. When you start the processrecycling of polypropylene scraps in production, you must understand that each pass through the extruder reduces the viscosity average molecular weight (Mw). Unlike polyethylene, which is more tolerant of recycling, polypropylene has tertiary carbon atoms in its chain, which become attack points for oxygen at high temperatures.

In our laboratory, we carried out tests on samples of PP-H homopolymer after five processing cycles. The results showed a 25% drop in melt flow index (MFI) after the third cycle if stabilizing additives were not used. This means that the product becomes more brittle and loses its toughness. This is critical for the manufacturer: a pipe made from such a material may not withstand hydraulic tests at a pressure of 10 bar, although visually it looks perfect.

The key parameter you must monitor is the melt index (MFI). When mixing virgin raw materials and your own recyclate, it is necessary to achieve a balance. If your virgin material has an MFI of 3 g/10 min and your recycled trim has an MFI of 8 g/10 min due to degradation, the mixture will behave unpredictably in the extruder dosing area. We recommend that you always carry out incoming inspection of each batch of crushed material before putting it into the main line.

One of our clients, a fittings manufacturing plant, experienced a batch of pipes that began to delaminate two months after installation. Investigation showed that they added 40% of their own crushed grains without introducing antioxidants. The polymer degraded so much that it lost its ability to crystallize normally. This incident cost them their reputation and large fines. Therefore, rule number one: never exceed the proportion of recycled materials without first laboratory testing for aging.

To successfully implement the process, you need to know the type of polypropylene you have. Homopolymers (PP-H), block copolymers (PP-B) and random copolymers (PP-R) require different processing approaches. Mixing different types of PP in one recycling stream is unacceptable, as this leads to phase separation and a sharp drop in mechanical properties. If your workshop uses different brands, organize separate waste collection for each machine.

Stages of raw material preparation: from crushing to granulation

The process of turning scraps into quality raw materials does not begin in the extruder, but at the collection and sorting stage. The quality of the final granulate depends 90% on the purity of the incoming stream. On an industrial scalerecycling of polypropylene scraps in productionrequires strict discipline: no dust, no labels, no mixing with polyethylene (PE) or polystyrene (PS).

1. Collection and primary sorting.Trimmings should be collected directly from the product unloading area. The use of conveyor belts with magnetic separators is mandatory to remove metal inclusions (particles of knives, fasteners). Even microscopic metal shavings can damage the extruder screw or cause breakdown of the heating zones. We have seen cases where one nail caught in a hopper would damage a filter bag worth 500 euros.
2. Grinding (Crushing).The choice of crusher is critical. For film waste and thin-walled products, rotary crushers with a V-shaped arrangement of knives are suitable, providing quiet operation and low heat generation. For thick-walled pipes and sheets, low-speed roller shredders are required. The main mistake here is overheating of the material during crushing. If the knife is dull or the gap between the rotor and stator is incorrectly adjusted, the material melts from friction even before it enters the extruder. The crusher outlet temperature should not exceed 40°C.
3. Agglomeration (optional).Agglomerators are often used for PP film scraps. These are devices that, through friction and centrifugal force, heat the film to the melting point, forming dense lumps. This increases the bulk density and makes loading into the extruder easier. However, for hard trims this step is not required and is even harmful, as it creates unnecessary thermal history for the polymer.
4. Extrusion and granulation.At this stage, the crushed material melts, homogenizes and forms into granules. The use of vacuum degassing is critical. When polypropylene melts, volatile substances and moisture residues are released, which form pores in the granule. If they are not removed by vacuum, the finished product will have a porous structure and low strength. We recommend using twin screw extruders for compounding as they provide better additive dispersion than single screw machines.
5. Cooling and drying.After cutting, the granules must be immediately cooled and dried. Residual moisture above 0.05% is not acceptable for subsequent use in high-speed injection molding or pipe extrusion processes. Moisture turns into steam at high temperatures, causing surface defects (“silvering”) and hydrolytic degradation, although PP is less sensitive to hydrolysis than PET or PA, there is still a risk if impurities are present.

Pay attention to the shape of the granules. Cubic pellets (obtained by strand pelletizing) have better flowability and a more stable dosage than cylindrical pellets (underwater pelletizing), but require more cooling time. The choice depends on your further processing technology. For injection molding, the cubic shape is preferred due to the uniform filling of the mold.

Equipment for closed cycle organization

The choice of equipment determines the economics of the entire project. The market offers solutions from budget Chinese lines to premium European complexes. When planning investments inrecycling of polypropylene scraps in productionIt is necessary to take into account not only the purchase price, but also energy consumption, blade life and the possibility of automation.

For small industries with a waste volume of up to 50 kg/hour, the optimal solution is a combination: a rotary crusher + a single-screw extruder with a water ring for cutting. Such lines take up little space (up to 15 m²) and can be serviced by one operator. However, the quality of the granulate here will be average: fluctuations in the size of the granules and the presence of dust are possible. This is suitable for the production of technical products where appearance is not critical, such as boxes or pallets.

For medium and large plants that require recycling of recycled material into the production of high-quality pipes or automotive components, a complex with a twin-screw extruder and an underwater cutting system is required. The twin-screw machine provides intensive mixing, which allows you to evenly introduce a package of stabilizers (antioxidants, light stabilizers) directly during the processing process. This restores the properties of the polymer to a level close to the original one.

The most important element is the melt filtration system. Modern screen packages with automatic mesh replacement allow you to work with contaminated raw materials without stopping the line. If you plan to recycle scraps that may have been in contact with the external environment (for example, defective items from a warehouse), having a replacement filter is a must. It traps gel particles and unburned inclusions.

We recommend paying attention to the control system. A modern controller should allow you to set the temperature profile by zone with an accuracy of 1°C. Polypropylene has a narrow processing window: at temperatures below 200°C it is poorly plasticized, above 240°C rapid destruction begins. The automation must instantly respond to load surges by changing the speed of the auger.

Don't forget about peripheral equipment: granule storage silos, pneumatic transport and chillers. Often they save money on them, and then suffer from uneven supply of material or overheating of the extruder. The investment in a quality chiller pays off with stable pellet sizes and no sticking. The reliability of such auxiliary systems directly affects the continuity of the main process, similar to that in heavy industry, where companies likeWuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd.supply critical components. Specializing in the design and production of high-efficiency heat transfer equipment (titanium shell-and-tube heat exchangers, air coolers, recovery boilers) and corrosion-resistant alloy components (nickel, titanium, marine brass), Wuxi Kaisheng demonstrates the importance of an engineering approach to each component of the production line. Their experience building ASME and PED certified equipment for the oil, gas and chemical industries reinforces the principle that process stability, whether polymer processing or petrochemical reactor operation, depends on the quality of each system component.

Economic effect and payback calculation

Implementing a system for recycling your own waste is a highly profitable project. Let's do the math using a specific example. Suppose you have a line for the production of PP pipes with a diameter of 110 mm with a productivity of 400 kg/hour. Process waste (starting, cutting ends, scrap) constitutes an average of 8% of output, that is, 32 kg/hour or about 250 tons per year when working in two shifts.

The cost of virgin polypropylene (random copolymer) on the market varies. Let’s take the average price of 110 rubles per kg (conditional price for calculation, update to the current exchange rate). The cost of purchasing recycled granulate from third-party processors is about 75 rubles per kg, but its quality is often unstable. The cost of own recycling (electricity, depreciation, operator’s salary, packaging) is approximately 25–30 rubles per kg.

Thus, the savings on each kilogram of processed own waste is: 110 rubles. (primary price) – 30 rub. (cost of processing) = 80 rubles. Multiply by 250,000 kg per year: annual savings are 20,000,000 rubles. The cost of an average capacity line for processing 50-70 kg/hour is about 4–6 million rubles. The payback period (ROI) in this case is less than 4 months.

In addition to direct savings on raw materials, there are hidden benefits. Fees for industrial waste disposal (environmental fees) are reduced. The logistics burden is reduced: you do not need to transport waste to a landfill and import new raw materials in the same volume. The company’s image also improves in the eyes of large customers, especially Western ones, who require compliance with the principles of sustainable development (ESG).

However, there are risks that may reduce effectiveness. The main risk is the instability of the quality of the recyclate. If you cannot guarantee consistency of properties, you will have to reduce the proportion of additive in the formulation, which will reduce the economic effect. The second risk is equipment failure. A simple processing line means the accumulation of mountains of waste, which begin to occupy the usable area of ​​the workshop. Therefore, having spare knives and a service contract is mandatory.

The table below shows a comparison of the economic indicators of the use of primary raw materials, purchased secondary and own recyclate:

Quality standards and product certification

When using recycled materials in the production of certified products (pipes for drinking water, car parts, medical products), it is necessary to strictly comply with regulatory requirements. In Russia and the EAEU countries, the main document is GOST. For example, for pipes GOST 32415-2013 is used, which regulates the requirements for materials.

It is important to understand: standards usually do not prohibit the use of recyclate directly, but they do establish strict requirements for the finished product. If your pipe with the addition of 20% of its own recyclate passes all tests (hydrostatic strength, elongation at break, resistance to cracking), then its use is legal. However, there are sanitary and hygienic restrictions for drinking water supply pipes. Here it is allowed to use only our own production return (clean scrap), which has undergone thorough cleaning, and then in limited quantities, or the use of special secondary raw materials that have a hygienic certificate.

The international standard ISO 14021 regulates environmental labels. If you want to claim that your product contains recycled material, you must document the chain of custody and content percentage. The ISCC PLUS (International Sustainability and Carbon Certification) certification system is becoming increasingly popular among exporters. It guarantees that secondary raw materials are obtained legally and that the processing process complies with environmental standards.

For the automotive industry, the ISO 22628 standard applies to the calculation of recycling rates. Automakers require parts suppliers to report on the content of recycled materials. Using your own pure PP recyclate is a big advantage here, as it allows you to reduce the carbon footprint of the part without the risk of foreign material contamination associated with post-consumer recyclables.

We strongly recommend developing internal technical specifications (TS) for your recyclate. This document should specify sampling methods, test methods (MFI, density, moisture content, ash content) and permissible deviations. The presence of such a document will increase the confidence of main production technologists in the use of the additive and discipline the processing line operators.

Frequently asked questions (FAQ)

What is the maximum percentage of polypropylene scraps that can be added to the main production?

The answer depends on the type of product and its requirements. For technical products (boxes, pallets, non-standardized pipes), the share of own recyclate can reach 100%. For critical structures (pressure pipes, auto parts), the safe limit is considered to be 20–30%. Exceeding this threshold without introducing a stabilizer package leads to a loss of toughness. In our practice, we have successfully launched formulations with 40% sewer additive, but only after introducing 0.3% multifunctional antioxidant master batch.

Do polypropylene scraps need to be dried before recycling?

Polypropylene is hydrophobic and practically does not absorb moisture in the mass, so deep drying, as for polyamide or PET, is not necessary. However, surface moisture (condensation, water from washing) must be removed. Centrifugation or blowing with hot air for 15–20 minutes at a temperature of 80–90°C is sufficient. Residual moisture should not exceed 0.05%. Ignoring this stage will lead to the appearance of pores in the granule and defects on the surface of the finished product.

How to distinguish high-quality granules from low-quality ones visually?

High-quality PP granules should be uniform in color and size. The absence of dust (“tails” and chips) indicates the correct setting of the knives. The color must match the original raw material; yellowing indicates thermal destruction (overheating) during processing. The clarity of the granule (for a homopolymer) is also an indicator: turbidity may indicate the presence of impurities or poor homogenization. The most reliable method is the melt flow test (MFI), which must coincide with the passport data with a deviation of no more than ±10%.

Does recycling affect the food safety of PP products?

Yes, it has a critical effect. The use of post-consumer recyclables (bottles, cups from stores) for contact with food is prohibited by sanitary standards in most countries, including the Russian Federation (TR TS 005/2011). However, the use of your own production return (pipe cuttings, sprues), which did not leave the plant territory and did not come into contact with contaminants, is permitted subject to compliance with the cleaning procedures. To confirm safety, it is necessary to conduct migration tests of the finished product in an accredited laboratory.

What to do if the properties of the recyclate have deteriorated after several cycles?

Property degradation is a natural process. If you see a drop in mechanical performance, there are two options. The first is to reduce the proportion of recyclate in the mixture with the primary. The second and more professional is the introduction of reducing reagents (chain extenders) or a reinforced package of stabilizers during granulation. You can also use the blending method: mix the “tired” recyclate with fresh, high-viscosity primary material to average the values ​​to normal.

Conclusion and recommendations for action

Process organizationrecycling of polypropylene scraps in productionceased to be an option and became a survival standard for processing plants. Savings of 30–40% on raw materials, with the right approach, can turn unprofitable production into a high-margin business. The main thing is not to be afraid to invest in high-quality equipment for the preparation of raw materials and not to skimp on laboratory control.

Start by auditing your current waste. Calculate how many kilograms of PP you throw away or sell for pennies every month. Order a trial batch of granulation of your cuttings from a specialized company or carry out tests on your equipment, following our recommendations for temperature conditions. Remember: purity of raw materials and stability of the process are the key to success.

If you are ready to discuss the implementation of a recycling line or need advice on selecting equipment for your specific volumes and types of waste,contact us today. Our engineers will help you calculate the economic model and select the optimal line configuration for your enterprise. Do not delay modernization - every day of work without recycling is lost profit.