Those who work in the plastics industry know that in order to obtain materials with specific performance (whether they are, for example, more resilient to the transformation process, more flexible, flame retardant or perfectly colored) it is necessary to carry out a sophisticated polymer processing process known as compounding.
At Gaypa, we offer you a complete guide to discovering this technology, which allows you to create tailor-made and high-performance raw materials.
What is compounding
Compounding is the process of mixing, melting and homogenizing one or more base polymers with additives, fillers, fibers and/or pigments. The aim is to modify the properties of the original polymer to create a new homogeneous material that is ready for final transformation (such as moulding or extrusion).
Explaining compounding in detail also means clarifying its basic difference with the masterbatch: while the latter is a concentrate of pigments or additives in a carrier polymer, which is dosed in small percentages (typically 1-6%) into the base resin during production, the compound is the final ready-to-use formulation. In particular, it contains the base resin, pigments and all necessary additives (such as stabilizers and flame retardants) in a single granule.
In practice, there is no need to add anything else: the compound is a “turnkey” product used mainly for high-volume industrial production, which requires absolute consistency and precision. Masterbatching, on the other hand, offers more flexibility for color changes and customizations.
How the compounding process works
Compounding is a controlled thermomechanical process that guarantees the homogenization of all components and which takes place almost entirely inside a twin-screw compounding extruder. The two screws, which rotate co-rotating or counter-rotating, are arranged in modular sections.
It all starts with the dosing of the components: the polymer base resin, fillers, fibers, powder additives or concentrated masterbatches are dosed with extreme precision in different areas of the extruder using gravimetric systems; Subsequently, the components are melted, mixed, dispersed and homogenized at high pressure and temperature.
This complex thermomechanical action ensures that even the most difficult-to-disperse additives, such as certain pigments or mineral fillers, are perfectly incorporated into the polymer matrix. Finally, the molten and homogeneous material is extruded through a die and subjected to pelletization (cutting into granules), cooling and packaging in bags or big bags, ready for final use.
Types of compounds for plastics
The versatility of compounding allows you to create product families with distinct functionalities. Let’s start with colored compounds, which arise from the direct incorporation of pigments or masterbatches into the base polymer, ensuring color uniformity for large production volumes.
Next, filled compounds represent a distinctive category and include materials with mineral fillers (such as talc or calcium carbonate) to increase their rigidity and thermal resistance, or with glass/carbon fibers to improve their mechanical properties. Technical thermoplastic compounds, on the other hand, are based on polymers such as PA (polyamides), PC (polycarbonate) and PBT (polybutylene terephthalate), which are often reinforced for applications in automotive and electrical engineering.
Thermoplastic elastomers (TPEs) are compounds that combine the flexibility of rubber with the processability of plastics, while flame-retardant compounds are flame-retardant (flame-retardant) formulations that are essential for construction and transportation. Finally, conductive compounds are used to discharge electrostatic charges or provide electromagnetic shielding in industries such as electronics.
Compatible polymeric materials and their behavior in compounding
In compounding, each polymer requires a specific approach, as each has a unique reactivity and thermal sensitivity. Here they are in detail:
- polypropylene (PP) and polyethylene (PE) are the most processed plastic commodities. They offer excellent advantages in terms of cost and lightness, but require UV stabilizers if intended for outdoor use. At the same time, their low polarity makes the dispersion of some pigments inorganic or complex charges;
- polyethylene terephthalate (PET) is known for its transparency and is used for bottles and packaging. However, it is extremely sensitive to moisture; This means that it must be pre-dried strictly to avoid breaking the polymer chains during extrusion (hydrolysis). It is often added with antioxidants;
- acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) are amorphous polymers known for their high mechanical strength. They require careful extrusion temperature management to avoid degradation and are commonly loaded with flame retardants or anti-UV additives for outdoor applications;
- Polyamides (PA, Nylon) are engineering polymers with excellent mechanical properties, but they are hygroscopic (absorbing moisture), which affects their mechanical properties and workability. They are often reinforced with fiberglass and require heat stabilizers and processing.
Additives, fillers and masterbatches
The success of a compound lies in the synergistic choice of all its components. Not surprisingly, compounding is the art of selecting the right additive to achieve the desired performance.
Additives and fillers are divided according to the function they perform:
- pigments give the final color to the compound;
- stabilizers protect the polymer from degradation due to heat, oxygen and light, increasing the useful life of the product;
- Flame retardants reduce the flammability of the material and are, therefore, essential for overall safety;
- mineral fillers, such as talc, calcium carbonate or kaolin, are added to reduce costs or increase mechanical properties such as rigidity and dimensional stability;
- the fibers, glass or carbon, are used to increase the tensile strength and stiffness of the material;
- lubricants improve the flow of the polymer into the extruder, reducing friction and improving machinability;
- Nucleating agents control polymer crystallization, improving dimensional stability.
Our expertise comes into play when compounders choose to integrate our masterbatches (such as the Raylen line for color or the Raytek line for functional additives) into their compounding process. This is because, although the compounder can add powdered pigments, the use of our masterbatches guarantees a higher and more uniform color dispersion, essential for “beautiful to look at” finished products. Our targeted formulation ensures that the pigment and additive integrate perfectly with the base resin of the compound, optimizing and maximizing the aesthetic and functional result.
Quality control and laboratory tests
To ensure that the compound meets specific requirements, strict quality control is required, which includes special laboratory tests. The most common and significant ones, which guarantee the conformity of the product, are:
- MFI (Melt flow index): measures the fluidity of the melted polymer and is essential to ensure the processability of the material in molding and extrusion;
- DSC (Differential scanning calorimetry): analyzes the thermal transitions of the polymer (such as melting points and crystallization), important for thermal stability;
- TGA (Thermogravimetric analysis): determines the composition of the compound by measuring the weight loss as a function of temperature, useful for quantifying fillers and additives;
- FTIR (Fourier-transform infrared spectroscopy): identifies the chemical structure of the polymer and additives, which is critical for material compliance;
- UV ageing test: evaluates the durability of the material when exposed to sunlight, which is essential for outdoor applications;
- Dimensional analysis and migration: check the stability of the dimensions and the possible tendency of pigments or additives to migrate.
Applications and sectors of use
Compounds are used in a wide range of industries and in the manufacture of countless products, thanks to their ability to combine strength and functionality.
In the automotive industry, they are essential for components placed under the hood (which require thermal and chemical resistance) and for interiors (which require UV stability and flame retardants); in packaging, they are used for special packaging that requires superior thermal or chemical barriers; in construction, they are used in profiles, insulation and pipes that require resistance to atmospheric agents and fireproofing; in household appliances, they guarantee aesthetics, electrical insulation and heat resistance; in the medical sector, they are used for devices that require biocompatibility and resistance to sterilization; in electrical engineering, conductive or high-performance insulating compounds are used; Finally, in food packaging, compounds must combine safety, regulatory compliance, excellent appearance and durability.
Why choose Gaypa
Choosing Gaypa, in partnership with Grafe, for your compounding projects means making the most of our historical expertise in color and additive manufacturing to obtain a final product with exceptional performance, both aesthetically and functionally.
Our customization capability allows us to develop specific masterbatches that integrate seamlessly into your compounding process: not only do we guarantee the precise reproduction of any shade, but we ensure that our pigments and additives do not compromise the final mechanical properties of the compound.
Thanks to our experience gained with customers from different sectors and the strength of an international team of technicians, we are ready to face even the most complex challenges, providing solutions that combine aesthetics, functionality and regulatory compliance.
Contact us for personal advice.
