Introduction to Modified Plastics: Basics and Production Processes

Introduction to Modified Plastics: Basics and Production Processes

The primary production equipment for modified plastics is the twin-screw extruder. The properties of modified plastics vary depending on the methods and additives used. Drawing on over 20 years of experience and technological innovation, Yinsu Flame Retardant Company now takes you through a simple understanding of the basics and production processes of modified plastics.

I. What are Modified Plastics?

The main component of plastic is resin. Therefore, its fundamental properties are primarily determined by the nature of the resin, but additives also play a significant role. Resin accounts for about 40% to 100% of the total weight of plastic. Resin is a high molecular compound that has not been mixed with various additives.

Plastic modification refers to any process that improves or enhances the original properties of resin through physical, chemical, or mechanical means. Plastics that have undergone modification are collectively referred to as "modified plastics."

The modification process can occur during the polymerization of the synthetic resin, known as chemical modification, such as copolymerization, grafting, and cross-linking. It can also take place during the processing of the synthetic resin, known as physical modification, such as filling, blending, and reinforcement.

In actual plastic production, a certain proportion of stabilizers is almost always added to prevent raw material degradation during storage, transportation, and processing. Therefore, non-modified plastics basically do not exist.

All plastics can be improved in aspects such as density, hardness, precision, processability, chemical properties, corrosion resistance, aging resistance, wear resistance, flame retardancy, barrier properties, and cost-effectiveness through modification methods.

Plastic modification is the most effective method to reduce costs and improve performance. It is widely used, especially in the recycled plastics industry.

II. Why Modify Plastics?

1. The Concept of Resource Recycling is Deeply Rooted

Global resources are always a major topic for humanity. The concept of resource recycling is deeply ingrained. Plastics are made from products derived from petroleum refining, and petroleum resources are finite. Therefore, recycling and reusing plastics can conserve petroleum resources and respond to the national call for resource conservation.

Recycled plastics often lose the properties of the original virgin plastic. To utilize recycled materials in producing new plastics, the process of plastic modification is inevitable.

Based on different needs, specific properties are enhanced to manufacture corresponding products, preventing resource loss. Only through resource recycling can true environmental protection and energy saving be achieved.

2. Expanding the Application Scope of Plastics

First, let's discuss the advantages and disadvantages of plastics.

Advantages: Most plastics are lightweight, good chemical stability, not easy to rust, good toughness, meaning good impact resistance, good electrical insulation, low thermal conductivity, easy to process, low processing cost.

Disadvantages: Poor heat resistance, flammable, prone to stress deformation, poor dimensional stability, not high strength, low temperature brittleness, poor solvent resistance, etc.

In practical applications, properties such as strength, flame retardancy, impact resistance, and processability of these plastics need to meet specific requirements to be applicable in the market.

For example, PP, as a general-purpose plastic, cannot meet the requirements for low-temperature performance, rigidity, and toughness in the field of automotive exteriors. Only after modifying PP material to enhance rigidity and toughness can it meet the usage requirements.

Daily applications often require plastics to possess multiple characteristics: both certain toughness and resistance to low-temperature brittleness, both insulation and stability.

The purpose of plastic modification is to broaden the application environment of raw materials and significantly enhance certain properties of the raw materials, thereby expanding the application scope of plastics. Thus, the significance of plastic modification is self-evident.

3. Synthesizing New Polymer Materials is Difficult, Neither Economical Nor Practical

From the birth of the first plastic product, the plastics industry has developed for 120 years. Thousands of polymer materials have been successfully synthesized, but only about a hundred have industrial value. Over 90% of commonly used plastics are concentrated in the five general-purpose resins: PE, PP, PVC, PS, and ABS.

Developing new polymer polymers not only requires huge investment but also has uncertain application prospects, being neither economical nor practical. Therefore, making good use of existing plastics and expanding their performance through modification technology is the most cost-effective solution.

III. What are the Methods of Plastic Modification?

1. Filling Modification (Mineral Filling)

Improves the rigidity, hardness, heat resistance, and other properties of plastic materials by adding inorganic (or organic) mineral powders to ordinary plastics. There are many types of fillers, and their characteristics are extremely complex.

Functions of plastic fillers: Improve plastic processing performance, modify physical and chemical properties, increase volume, reduce costs.

Requirements for plastic additives:

• Chemically inert, does not react adversely with resin and other additives.

• Does not affect the water resistance, chemical resistance, weather resistance, heat resistance, etc., of the plastic.

• Does not reduce the physical properties of the plastic.

• Can be filled in large quantities.

• Low specific gravity, does not significantly affect the density of the product.

2. Reinforcement Modification (Glass Fiber/Carbon Fiber)

Reinforcement measure: Adding fibrous substances such as glass fiber or carbon fiber.
Reinforcement effect: Can significantly improve material rigidity, strength, hardness, and heat resistance.
Negative impact of modification: But many materials may lead to poor surface quality and reduced elongation at break.
Reinforcement principle:

• Reinforcing materials have high strength and modulus.

• Resins have many inherent excellent physical, chemical (corrosion resistance, insulation, radiation resistance, instant high-temperature ablation resistance, etc.), and processing properties.

• After the resin is compounded with the reinforcing material, the reinforcing material can enhance the mechanical or other properties of the resin, while the resin can bond and transfer load to the reinforcing material, giving the reinforced plastic excellent properties.

3. Toughening Modification

Many materials lack sufficient toughness and are too brittle. Toughness and low-temperature performance can be improved by adding materials with better toughness or superfine inorganic materials.

Toughening agent: An additive added to the resin to reduce the brittleness of the plastic after hardening and improve its impact strength and elongation.

Common toughening agents – mostly maleic anhydride grafted compatibilizers:

• Ethylene-Vinyl Acetate Copolymer (EVA)

• Polyolefin Elastomer (POE)

• Chlorinated Polyethylene (CPE)

• Acrylonitrile Butadiene Styrene Copolymer (ABS)

• Styrene-Butadiene Thermoplastic Elastomer (SBS)

• Ethylene Propylene Diene Monomer (EPDM)

4. Flame Retardant Modification (Halogen-Free Flame Retardant)

In many industries such as electronics, electrical appliances, and automotive, materials are required to have flame retardancy, but the inherent flame retardancy of many plastic raw materials is relatively low. This can be achieved by adding flame retardants.

Flame retardant: Also known as fire retardants, are functional additives that impart flame resistance to flammable polymers. They are mostly compounds of elements from Group VA (Phosphorus), VIIA (Bromine, Chlorine), and IIIA (Antimony, Aluminum) of the periodic table.

Compounds with smoke-suppressing effects like molybdenum, tin, and iron compounds also belong to the category of flame retardants. They are mainly suitable for plastics requiring flame retardancy, delaying or preventing the combustion of plastics, especially polymeric plastics. This makes them harder to ignite, increases ignition time, and promotes self-extinguishing.

Plastic Flame Retardancy Ratings: Increase stepwise from HB, V-2, V-1, V-0, 5VB to 5VA.

5. Weathering Modification (Anti-Aging, UV Resistance, Low-Temperature Resistance)

Generally refers to the cold resistance of plastics at low temperatures. Due to the inherent low-temperature brittleness of plastics, they become brittle at low temperatures. Thus, for many plastic products used in low-temperature environments, cold resistance is generally required.

Weathering Resistance: Refers to the series of aging phenomena that occur in plastic products due to external conditions such as sunlight exposure, temperature changes, wind, and rain, including fading, discoloration, cracking, chalking, and strength reduction. Ultraviolet radiation is a key factor promoting plastic aging.

6. Modified Alloys

Plastic alloys are new materials prepared by physically blending or chemically grafting/copolymerizing two or more materials to achieve high performance, functionality, and specialization. The goal is to improve the properties of one material or combine the characteristics of multiple materials. They can improve or enhance the performance of existing plastics and reduce costs.

General-Purpose Plastic Alloys: Such as PVC, PE, PP, PS alloys are widely used, and their production technology is commonly mastered.
Engineering Plastic Alloys: Generally refer to blends of engineering plastics (resins), mainly including blend systems based on engineering plastics like PC, PBT, PA, POM, PPO, PTFE, as well as ABS resin modified materials.
The usage growth rate of PC/ABS alloys ranks among the top in the plastic field. Currently, research on PC/ABS alloying has become a hotspot in polymer alloy research.

7. Other Modifications

Such as using conductive fillers to reduce the resistivity of plastics, adding pigments/dyes to change the material's color, adding internal/external lubricants to improve the material's processing performance, using nucleating agents to change the crystalline characteristics of semi-crystalline plastics to improve their mechanical and optical properties, etc.

From extrusion temperature to screw configuration, from filler dispersion to surface grafting of flame retardants, every gram of performance in modified plastics lies in the process details. Only by optimizing the shear, residence, and cooling curves within the barrel can halogen-free flame retardants achieve an "invisible" distribution and efficient char formation in polyolefins. There are no shortcuts in material upgrading. Only dual precise mastery of both equipment and formulation can transform a laboratory recipe into a stably mass-produced "safety barrier."