Going Green with Purging Compounds

by Andrew Reeder, Moulds Plus International

A company going green is not only socially responsible, but also financially responsible. The best way for plastic processing companies to go green is by reducing waste. Waste is present in many forms. The two most common forms of waste are scrap resin and wasted energy. Hence, using an effective purging compound will reduce both scrap resin and energy waste. ­This article will discuss the reasons for going green and how to go green by using a purging compound. A case study showing the savings from using a commercial purging compound will be presented as well.

Why Go Green

An environmentally conscious company will not hesitate to take appropriate measures and adopt green manufacturing practices. Many times the transition is not simple but in the long term there will be a substantial pay off. The environmental dividends gained by green manufacturing cannot be measured in dollars and cents; it is measured in the quality of our air, water and less reliance on fossil fuels. Thus, plastic processing companies have the ability to reduce their carbon foot print by instituting lean manufacturing techniques along with using a quality commercial purge compound when purging their machines.

An altruistic company that goes green in order to help the environment is viewed  as noble. However, it is understandable that a company is hesitant to invest money to go green since a company exists for the purpose of being successful and profitable.  Fortunately, going green can also be a smart business model to help reduce production costs which will then increase the profit margin. An initial investment may be needed but in the long term there will be an increase in profits due to the reduction in manufacturing costs.  Purging a machine in the most efficient way is only one example of lean manufacturing. There are potentially many sectors in a plastic processing plant that may use lean manufacturing in order to make a company more profitable and green.


Purging a plastic processing machine can be financially and environmentally expensive. Using resin to purge a machine requires a large of amount of energy due to the extended period of time it takes to clean the machine.  Purging a machine with resin also produces a substantial amount of scrap because a large amount of resin is required to pass through the machine in order to clean it. Therefore, in order to reduce waste and make purging more efficient, companies should use a commercial purging compound.  It is true that a purging compound costs more per pound when compared to natural resin. In comparison to the higher price per pound for a commercial purging compound using resin to purge results in excessive amount of scarp produced, unnecessary energy consumed and production time lost.  All these factors result in a much larger monetary and environmental loss from using resin to purge.

Recyclable Purging Compounds

It is also important to note that not all purging compounds are equal. Conventional purging compounds may reduce scrap and energy, however, very few are recyclable. The scrap produced by recyclable purging compounds may be either included with regrind and made into parts or sold to the plastic processor’s scrap dealer. Purging compounds that are not recyclable must be thrown out; this then ends up in a land fill and results in a less environmentally friendly method of purging. Throwing out purging scraps also lowers profits because funds are not recouped by selling it to the plastic processor’s scrap dealer or including it with regrind to make parts.  It is recommended to check with your purging compound supplier to see if recyclable grades are available.

Areas to Use a Purging Compound

There are four different areas in production where scrap and energy may be reduced when using a purging compound. Traditionally the largest factor contributing to waste for processors are dark to light color changes. Using resin to purge a machine will require many press barrel capacities to remove the dark color which will result in greater waste and more downtime. On the other hand, using an efficient purging compound will require only one press barrel capacity to clean the dark color from the machine.

Excessive waste is also common during material changes.  Custom molders commonly need to address this issue because of the many different resins they work with on a daily basis. In many situations the previous production resin will remain in the machine and be a source of contamination. In these situations, using resin to purge the machine will take much longer than a commercial purge compound.  Therefore, companies that work with a wide range of resins should invest in a multi-purpose grade of purging compound that will be effective at purging a wide spectrum of resins.

The third common need for a purging agent is when carbon (shows up as black specks) becomes a contamination issue. The best way to battle carbon problems is to use a purge compound in a preventative maintenance fashion.  If the build-up of carbon becomes excessive the only viable way to clean the screw is to pull it apart and clean it manually. Thus, using a purging compound in the beginning stages of carbonization will result in reduced scrap and energy and ultimately increase production.  Therefore, it is highly recommended to use a purge compound on shut down and start ups in order prevent carbon from forming on the screw.

Case Study

It is understandable that businesses need to justify the investment involved with using a purging compound. Thus, data needs to be collected over a large span of time in order to quantitatively demonstrate the environmental and monetary savings from using a purging compound. Data should be collected on the present purging procedures (w/out commercial purge compound) and on the prospective commercial purging compound.  The data collection should include downtime, scrap resin produced and the amount of purging compound needed. Every plastic processing piece of equipment is unique in terms of power usage. Therefore, downtime will have to be interpolated into power usage for each piece of plastic processing equipment because of this variance.

Below is a graph comparing the cost of using resin to purge a machine versus the cost of using Ultra Purge (a commercial purging compound). The trial was performed on a 300 ton injection molding machine (with hot runners) going from red HDPE to white HDPE. Using the Ultra Purge resulted in a 55% reduction in material costs and a 75% reduction in downtime (machine time = $300/hr). The total savings accredited to using the Ultra Purge for this trial was $1,001.00. Also note that the Ultra Purge grade used in this trial is 100% recyclable. Please consider the energy consumption was not estimated because the hourly power usage for this particular injection molding press was unknown.


As the global population grows and technology advances, it becomes more important that companies take action in order to reduce their carbon footprint. A collective effort to decrease scrap resin and energy consumption by plastic processing companies will equate to a large global effort in conserving energy/resources and reducing pollution. Reducing a company’s carbon footprint will not only be good for the environment but also good for business. The majority of antidotes to reduce waste will also reduce productions costs. Due to the environmental pressures being placed on the earth and the hard economic times, all companies should be investing in ways to become more green and competitive in the world wide market place.

Moulds Plus International is the manufacturer of Ultra Purge, a purging compound for thermoplastic injection molders, blow molders and extrusion companies.  Moulds Plus International has offices and distributors located around the world to assist customers on a global level.  Moulds Plus International offers free samples of Ultra Purge and in-plant consultations.  For more information please contact us at 1 (517) 545-7987 or online