Procedures for silicone cookware recycling

1. Introduction

Silicone has many uses in medical, commercial and industrial situations being a heat resistant, durable, stable and relatively inexpensive polymer. Silicone is a type of rubber offering some very useful properties that make it ideal for use in a wide range of industries. It offers thermal stability across extremes of temperatures, from around minus 148° F to about 482° F. Silicone repels water and creates watertight seals, it has anti-microbial properties, is hardwearing, resistant to environmental effects such as oxygen and UV light and its low thermal conductivity makes it ideal for use in fire and heat protection. The high tear strength, electrical conductivity and the flame-retardant properties of silicone make it a safe product for use at home, in the office and in a factory. Popular uses for silicone rubber products at home include baking and food storage, household electronic products, personal care products, clothing and footwear, arts and crafts, mold making, children’s toys, building , hardware and lubricants.

2. Recycling procedures

Recycling silicone is a great way to save money, reuse products and contribute to caring for the environment. It requires just a few easy steps and some basic equipment. Grinding old silicone down, preparing a mold, and mixing shredded silicone with fresh silicone is an easy way to create a wide range of rubber-based products. [1]

Recycled silicone is available in a wide range of colors and is able to be color matched as required. It is not only available as a rubber, but also comes in the form of silicone caulk, silicone resin, silicone gel, silicone grease and silicone oil.

2.a Steps to recycling silicone

One can recycle silicone at home with a few basic pieces of equipment and some simple techniques. Many people like to recycle silicone rubber they have available around the house instead of throwing it in the trash. Recycling silicone involves grinding it down, preparing a mold and then mixing the shredded silicone granules with fresh silicone.

2.b. Grind down old Silicone for recycling

To recycle silicone, grind down the old silicone into small, shredded pieces. One achieves this with either some craft scissors or a blade. If a large amount of silicone is being recycled, a kitchen grinder is an ideal option. Silicone is available in a range of strengths or hardness levels, described as a Shore A or IRHD from one to 10. The higher the number, the harder the silicone when set. Hard silicone rubbers, such as those with a Shore A 50 to 55 grade, and soft flexible silicone rubbers with a lower grade, such as Shore 20 to 25, easily grind down into small shredded granules using a manual metal kitchen grinder. For even finer silicone granules, run the silicone through the grinder a second time.

2.c. Prepare the mold for the recycled silicone

The majority of people recycle silicone to make flexible, easy to use molds for a wide range of purposes, from cooking and cake decorating to construction molds and casting molds. The type of mold shape depends on what one wishes to make. Either create a mold from scratch or use an object of the desired shape.

2.d. Mix recycled Silicone with fresh silicone

Once the silicone is ground sufficiently and the mold is ready, it is time to mix the recycled silicone with some fresh silicone. Fresh silicone is readily available in powder form as well as liquid form. Silicone molding kits are the ideal option for those new to silicone recycling. It usually takes some trial and error when determining the amount of recycled silicone shavings to add to the fresh silicone mix. Using too much recycled silicone results in a product with less strength.

Because fresh, or uncured, silicone exists as a liquid or gel, consequently it requires curing to convert it to a solid state. Catalyzing, vulcanizing or injection molding recycled silicone are the various ways of converting it to a solid state.

Researchers in China have developed a new technique for recycling silicone, the rubbery plastic substance being used in an increasingly large number of cookwares [2].

Silicone is a compound with organic and inorganic components; its backbone of silicon and oxygen is found in common sandstone, meanwhile the other compounds they are mixed with are synthetic.
The resulting product is chemically stable, not very reactive with other chemicals or at high temperatures and is difficult for other compounds to stick or bind to. It’s waterproof, hypoallergenic, and doesn’t transmit unwanted chemicals to human bodies. It also doesn’t decompose, ever. Silicone is therefore used in many applications from cookware and sealing caulk, to cosmetic micro beads and breast implants.

Scientists already have other techniques for recycling silicone, but they’re expensive. That’s because it is very energy-intensive to strip the substance down.

Some types of low-grade silicone can be broken down to their chemical components and reused, but the methods are expensive and the processes are complicated.

The new recycling process is less energy-intensive and puts the super-water-resistant product to practical use, notably as insulation and as a component of self-cleaning glass.

The procedure is also surprisingly simple. Chinese researchers took a piece of processed silicone ( e.g. a cupholder or non-stick pan ) and cut it into smaller pieces. Then, the pieces are held in the flame of an alcohol lamp in the air until the they were completely burned. Once the silicone was sufficiently charred, the researchers used a hot press to compress it into a solid or pulverize it into a powder.

The result is a substance with a coarse, durable surface that is water-resistant due to the honeycomb-like nanostructure trap air that doesn’t let water near the surface itself. The researchers even tested its durability with sandpaper and found that it held up surprisingly well, though not perfectly. These are features that scientists have been trying to develop for a long time, drawing inspiration from water-resistant natural materials like lotus leaves and spider silk.

Being highly durable, such rubbery materials are also useful for insulating high-voltage outdoor electrical facilities, like solar panels. The powdered form is also water-resistant and can withstand at a number of conditions and temperatures, which makes it useful when incorporated in self-cleaning glass, or the coating that can be used on the outside of the solar panels themselves.

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