Effects of pigments in dry mixing: What REALLY happens to physical properties?

Dr. Nick Henwood

Many parts of the North American roto industry still rely on using dry color materials.  The main reasons for this are reduced cost and operational convenience. However, it is generally recognized that using dry color, rather than fully compounded pre-color, can result in a significant loss of material properties.  

If you’ve sat through as many ARM meetings as I have, you’ll have heard many different opinions voiced on the negative effects of using dry color and whether these effects can be mitigated.  As a scientist, my normal response to strongly held opinions is: “Do you have any data that supports this?” Unfortunately, when it comes to questions of dry color, there seems to be a dearth of hard data available to support us in making sensible decisions.

A study presented by NOVA at the recent ARM Montreal conference was an excellent first step to defining what variables do and do not have real significance.  This confirmed the findings of any earlier study (by me, in a previous role), that the two most critical factors were pigment addition rate and pigment type.

The Roy Crawford Research Education and Development Foundation have just provided funding to further increase our industry’s knowledge in this important area.  A new study will be undertaken, which builds on earlier work. Six of the most common pigments used to produce dry color blends will be evaluated in detail for their effect on material properties, particularly impact strength.

A key stipulation of REDF funding is that the results should be widely disseminated and that inclusion of other interested parties should be encouraged.

As the lead researcher on the project, I would now like to invite all parties with an interest in this area, and expertise to contribute, to become involved.  I’m proposing that we form a special interest group, from which I can draw opinions and information and who I can keep abreast of developments, as the project proceeds.

Ultimately we plan to present the results of the finished study at the 2019 ARM Meeting in Houston, Texas.

If you would like to join in, please contact ARM Executive Director Adam Webb and let him know.  Adam will then form the group and act as the conduit for my regular updates on the project.

In closing, I should thank the Roy Crawford Foundation for their funding and also ExxonMobil Chemical Canada, who have contributed a batch of base resin for the study.  The ARM Board of Directors have, as always, been extremely supportive.

Dr Nick Henwood serves as the Technical Director for the Association of Rotational Molders. He has 25 years-plus experience in rotomolding, specializing in the fields of materials development and process control. He operates as a consultant, researcher and educator through his own company, Rotomotive Limited, based in UK.

3 responses to “Effects of pigments in dry mixing: What REALLY happens to physical properties?”

  1. Great blog entry Nick!

  2. Hit enter a little too soon on my last comment. Anyway, I am excited about this project and what we are going to learn from it.

  3. Nick
    Don’t know what you need as input …etc. but count me in if you can use me and my knowledge/experience

    There was an ARM presentation on pigments that may have had DATA on this at a Spring meeting in Hawaii in 1998. May be worth having ARM look to see if they have any papers on it from that meeting.

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