Chemical Recycling Graphic
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Recycling Polymer Composite Materials: Motivations and Methods

Polymer composite materials are attracting the attention of manufacturers now, more than ever, for application in the field of medicine, furniture, automobile, construction, and aircraft appliances.  

What are Polymer Composite Materials?

Composite materials are combinations of two materials with different chemical and physical properties. By combining these, we obtain a material which has the chemical properties of both materials and can be used for special-purpose application.  Polymer composite is a homogeneous material produced by systematic and synthetic assembly of polymers and reinforcement to obtain specific properties. Here, polymeric material act as a matrix, and fibers act as reinforcement in the composite. Matrix binds and protects reinforcement fibers. 

Popular polymeric materials used as a matrix are epoxy, vinyl esters, and polyester thermosetting resins.  Sometimes, thermoplastic polymers also used as a matrix. Fibers are load-carrying members and provide strength to the composite structure. Commonly used fibers are glass fibers, carbon fibers, aramid fibers. Sometimes fillers are also added to the composite for additional properties.  

How are Polymer Composite Materials Recycled?

Since the polymer composites are made of thermoplastic and thermosets, the thermoplastic composite can be easily recycled with less degradation of recovered polymer matrix material and reinforcement fibers. On the contrary, with thermosetting composites, it is not so easy to recover polymer matrix and reinforcement fibers without degradation in properties, because the matrix in thermosetting composites is cross-linked. For thermosetting polymer composite, mechanical processes are widely used to reduce the size of waste in the form of fine particles. Chemical and thermal processes are utilized for breaking down the material in another useful form or create energy from that material by incineration, fluidized bed and pyrolysis are the majorly used thermal recycling process. The primary focus in recycling thermoset polymer composites is the reinforced fibers, like glass fibers, carbon fiber, etc. These fibers have more value than the polymer matrix. Therefore,  it is beneficial and much preferable to remove those fibers materials out of that composite waste.  Recycling reduces the landfilling and the consumption of fibers too.  

Why Should Industries Recycle Polymer Composite Materials?

The Motivation behind recycling polymer composites is simple. There are mainly two advantages associated with recycling thermoset polymer composite waste, the cost of virgin fibers produced and the environmental benefits, such as disposal by landfill. Companies like Suman Chemical Industries utilize thermoset composite waste as a secondary resource to produce fiber recyclate. This is important because the production of virgin fiber is energy-intensive and costly as well.  

Hierarchy for approaching composite waste material in decreasing order of  desirability:

• Restrict misuse through prevention at source while manufacturing  

• Recycling

• Reusing

• Incinerate to decompose the waste

• Incinerate with energy and material recovery 

• Incineration for only energy recovery  

 Landfilling must be our last option for dealing with waste composite materials.  

Challenges Faced During Polymer Composite Recycling:  

Recycling of polymer composite has many advantages and hence is gaining more importance nowadays. But there are also some challenges associated with the whole process of polymer composite recycling.

• Composite materials are a mixture of reinforcements (like carbon fiber, glass fiber, etc.), matrix materials (like epoxy, polyurethane, etc.), and fillers (like particles, colorants, and fire retardants). Hence, compatibility between these materials is different and sometimes processing is complex

• Remolding of Thermosetting resin is not possible since it is cross-linked  

• The basic obstruction is the contamination in the recycling process  

• Separation of scrap is very challenging as well as a complex process  

• Sometimes the recyclable composite product has inconsistent supply, which restricts the long-term business. 

Our Approach to Recycling:

Methods of recycling composite polymer materials
Classification of recovery and recycling technologies for thermosetting polymer composites

Thermal Recycling: 

Here thermal (heat) energy is utilized to break down the material into its original component and hence those component’s reinforcement can be reused. Widely used thermal techniques for recycling are fluidized bed and pyrolysis.  

Fluidized-bed:  

The principal purpose of this research is the recovery of reinforced fibers because these have more eminent recycled substance value as compared to filler and resin components. This technique works by thermally decomposing chopped segments of composite in the silica sand bed and fluidizing it using air at nearly 450–500 ◦C. The organic resin is volatilized, and filler and fiber particles depart the resin, and it will obtain as we need. The volatilized organic components are combusted for energy and heat recovery, while the filler and fiber particles can be reused in modern composites. 

Fluidized bed recycling process in Polymer Composite Recycling
The principle of the fluidized bed recycling process

Pyrolysis  

The pyrolysis method leads to the degradation of material by heating without oxygen and converting it to simpler molecules. This procedure applies to polymer composite to break down resin matrix into more purified gas and liquid, which then recovered and used along with new reinforcing and filler  material in a new composite  

Chemical Recycling:  

Chemical recycling procedures involve the degradation of the polymer matrix of composites into chemicals, which can be further used as fuel or to manufacture novel polymers.  Using this process, we recover polymer as well as re-useable fillers and reinforcing materials from the thermosetting polymer composite. Chemical recycling includes recycling using solvolysis, supercritical fluid, high concentration acid, and hydrolysis  

CFRC Degradation by Chemical Recycling in Polymer Composite Recycling
General schematic of CFRC degradation by chemical recycling

Mechanical Recycling: 

The mechanical recycling technique includes the reduction of the size of waste to reinforce it into different materials. A large number of studies are available on mechanical recycling. The mechanical recycling technique is the only technique that is adopted commercially for processing waste Sheet Moulding Composites (SMCs).  

Steps of Mechanical Recycling in Polymer Composite Recycling
Steps Included in Mechanical Recycling

Summary of Recycling Techniques

ProcessAdvantagesDrawbacksEnergy Required
Mechanical Recycling – Do not use or produce  
hazardous materials  
– Both Fibres and Resin recovered
– Significant degradation of  
mechanical properties  
– Limited possibilities of re 
manufacturing
0.1-4.8 
(MJ/Kg)
Chemical Recycling – Potential for recovery of material from the resin
– The very high holding of mechanical properties and length of fibre
– Low concentration tolerance
– Reduced scalability of most methods
– Hazardous solvents used
21-91 (MJ/Kg)
Fluidized Bed recycling– Very high tolerance to the concentration
– The process is well organized as well as documented.
– Absence of residual char on the fibre surface.
– Degradation of strength is between 25% to 50%
– Degradation of Fiber length
– The fuzzy architecture of fiber
– Recovery of the material of resin is a bit impossible
5-40
(MJ/Kg)
Pyrolysis– The high holding of mechanical  properties  
– Having the potential for  
recovery of the chemical  
feedstock of resin.  
– No need for Chemical solvents here.
– Char is deposited over the fibre surfaces  
– Very sensitive to properties of  recycled fibres with processing parameters  
– It is environmentally dangerous  off-gases
24-30 
(MJ/Kg)

Suman Group of Companies provide solutions to the problem of recycling by using different methods of recycling. One can re-obtain reinforcement fibers, and use thermal recycling to recover the thermal energy from which the matrix can process residue metrics further. Recycled composite materials are comparatively cheaper than virgin composite materials, so recycling is economical. The energy recovery from different polymer composites reflects that an enormous amount of energy is available for recovery. Concisely, a large amount of recovery is possible, either in the form of materials or in the way of energy.

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