Phase change materials offer innovative solutions for saving energy

Increasing energy costs impact everyone with respect to ability to maintain a decent standard of living. Daily costs are rising faster than ones rise in earnings! Further, as climatic changes become erratic, energy has become all the more important to sustain the standard of living. Renewable energy replaces conventional fuels in areas like electricity generation, space heating and water heating. Highly touted renewable energy sources such as wind or solar PV are not cheap and are inefficient when compared with traditional sources of energy. Focus is shifting to greener and sustainable methods that have the ability to capture waste or free thermal energy.
 
Phase change materials (PCMs) are suitable for storing thermal energy in the form of latent heat and release when required by changing its phase from solid to liquid and vice versa. They absorb or release large quantities of heat at a constant temperature thereby maintaining desirable ambient conditions. Studies conducted to compare phase change (latent heat) and sensible heat storages have shown that a significant reduction in storage volume can be achieved by using PCM as compared to sensible heat storage. Phase change materials find their application in cold storage, temperature controlled food transportation, pharmaceutical transportation, air conditioning, solar applications, thermal wear, building cooling and heating and in fact any industry looking to exploit off peak electricity tariffs for heating or cooling or capturing freely available energy (and we have lots of it – cold nights for warm days and warm days for cold nights!)

Conventionally, PCMs have been in the form of liquid which are encapsulated in drums, pouches, or plastic panels. PCMs in liquid bears the risk of leaking out in case of packaging defects or mishandling.  
 
Form stable PCM
These PCMs are made using polymers in combination with PCMs. The blends formed using polymers act as shape stabilisers and do not allow the PCM to flow from its matrix and it is therefore called form stable PCM. Phase change material is entrapped in the polymer matrix because of mechanical interaction with the polymer chains. These innovative materials for storing energy over conventional PCMs bear the advantage that any mishandling or packaging defect will not lead to leakage of the PCMs at application site.
 
These materials are nontoxic in nature, flexible, have high latent heat (above 200 kJ/kg, and is the most desirable property for any PCM in any application), high tensile or tearing strength both above and below the melting point of the PCM. Further, it is so stable that it can easily be heated and cooled without leaking out its phase change material. The form stable PCM provide stored heat that has improved safety and handling ability.
 
These materials are now being tried in jackets for human comfort. People and in particular the country’s defense forces, living in remote areas suffer harsh weather conditions. Form stable PCMs provide the optimum temperature to the body. Any raw PCM when in solid state causes discomfort to the user while working. Using form stable PCM enables the user to bend and do any kind of work with complete flexibility. Moreover, the user always remains protected from any kind of leakage as it is the polymer which is in contact with the body and the chemical is entrapped in the polymer matrix.

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These materials have been further enhanced by making them microwaveable. Susceptors in the material initiate uniform melting of phase change material when exposed to microwave irradiation. This microwavable PCM is free of sparking, arcing and local overheating. These phase change materials can be cast or moulded in any desired shape. Such polymer based PCMs can be charged by domestic microwave oven for just one to two minutes prior to use depending upon the amount of PCM .These materials have been appropriately reinforced to give a composite which has high tensile and tear strength both above and below the melting point of phase change material.
 
The next question is fast charging in a microwave oven! Poor thermal conductivity limits effective charging in microwave oven. Several technological issues such as sparking or hot spots have been effectively addressed too. With the thermally conductive materials, the heat instantly gets transmitted to adjacent particles. Moreover, the thermally conductive material removes sparking or over heating during microwaving and provides uniform heating and uniform discharging of the said material.
 
One application is to use these materials as portable ‘ovens’ for keeping food warm over long duration. The product is a simple, low cost, safe and easy to use. These have been incorporated into lunch boxes to keep their contents hot for long duration. It is an effective and efficient method of keeping food hot during long office hours or journeys for users. Elements accessories has launched a lunch box in US called ‘Lava Lunch’ using the same form stable phase change materials. It keeps the food warm for a period of six hours and won the Baby + Child Best New products award presented at NY NOW.

Form stable products bear the uniqueness of being substantially shape stable, highly conductive, high mechanical strength, reinforced, leak proof, and microwavable. This development has catapulted India into one of the few countries making shape stabilised PCMs.
 
These materials enable low cost thermal energy storage solutions for the developing world. The materials can be transformed into a variety of shapes, sizes and forms; find applications in jackets, apparel, thermal seat cushions, table ware items, hot plates, food warmers, medical wraps, cooling lithium ion batteries, tea coasters or covers for tea cups, seat covers in cars, solar heating application, dining mats, liner of helmet, cold chain transportations, and any heating and cooling applications where leakage is to be avoided. There are immense possibilities for entrepreneurs and companies alike to create a variety of products using these materials!
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Samit Jain is the Managing Director of Pluss Polymers Pvt Ltd
Nidhi Agrawal is the Associate – R&D at Pluss Polymers Pvt Ltd