Vol 2 No 6 

 

Hallo!
 
Will we have some spring in Washington this past week or so, just in time for the summer which I believe starts in a few days! Understand we were still getting snow at 4,000 feet a few weeks ago and the ski slopes were open.
 
The article this month is on Additives for plastics but just filler's this time. I know a boring subject but always fun to process, and build tools for. At the recent K show there again was the compounding injection molding machines making their own filled product/part in one shot. I believe Jeld-WenŽ the door and window people are doing so with a door.

 

New or hope so is an archive of past articles so if you just joined the mailing list check out the link: http://archive.constantcontact.com/fs034/1101663388820/archive/1102138661635.html 
 
On the personal side I am off to California this weekend for a few weeks of work, so any in the San Francisco area that may need some help I may have a few days open give a call or email, time and travel expense to area is already covered. I'll be working with acrylics and ceramics in a coating application which should be fun.  Last month we (family) updated the yard at mom's house, got the nieces and nephews to pull weeds and move dirt. It came out great, and all the plastics in the drip and irrigation work great now too (my part) though have a few complaints as to why water is spraying this and that, hard to explain that they do not make a 10 degree spray head, or one that is 65 degrees.
 
Enjoy the summer, fall, winter which ever it is trying to be at your location. Think about preparing for the upturn in business, best to always be prepared though it is hard to do at times when the future does not look so bright.
 
TA-
 
Steven
 
Silveys Plastic Consulting
360-882-3183
silveysplastics@aol.com
silveysplastics@hotmail.com

 
Definitions: Additive: added to, Filler: 1.reinforcement to improve physical properties, 2.take up space, to extend, reduce amount of polymer used, 3. to improve its electrical conductivity
 
In some ways additives are a double edge sword, in that they can help and also hurt in the finished part and more importantly the processing of the material. Some would say that when we add ingredients to our material we are placing garbage in the material and now have created something new, or not the same as the original material. The additives can be added at the original manufacture of the material, a compounder, or possibly press side in your plant. Please note that all materials have some sort of additive in them from the original material manufacture and these are the processing aids, which help slip, heat, and stabilization and are additives in the sense of something added to the base resin. AS a processor consumer of materials the common ground is to think of this as part of the raw material and not what we would consider additive. Please note that if you the processor add to the material as it comes from the supplier than you become the responsible party for the material.
 
What we are speaking about in this paper are the additives as classified as fillers. Though there are many other additives and further papers will discuss those, for example, blowing agents, colorants, etc.
 
When talking about fillers as mentioned in the definition there are 3 basic classes and it could be said variation amongst those.
 
Reinforcement,
 
With reinforcement the properties of the polymer are enhanced. These can be greatly enhanced or moderately enhance dependant on the loading. In most cases the use of reinforcements does not preclude the alteration of our processing cycle though in truth we do have to be aware of it and to get better properties and aesthetics we would alter. Understand the terminology in that when we reinforce the additive is most likely sized with a coupler so that there is adhesion achieved between the sizing agent and the filler and the polymer, in some cases think of it as becoming one uniform mass.
This is what reinforced typically means, or chemically coupled.
 
When we reinforce the polymer we will achieve higher physical properties within our polymer but at the same time we may loose other properties. For example glass fiber is often used and the amounts vary, but what is typically achieved is an increase in tensile strength, flex modulus etc. But what is lost is the elongation or stretching of the polymer matrix. Understand it will take a higher strength to cause our product to start to elongate, but the elongation now will be less than previous. Where this may come into play would be inserts for threads in our product. Previous with no filler we might have had 10 to 20% elongation, and thus the pressed in insert would only stretch and no issue observed. Now with filler the elongation is down to 5% and all of a sudden in the field it is observed that the insert area is cracking, especially at the weld line. (See below)
 
Extenders/ fillers
In using the above term we have to be aware that small particles such as clays, wood flour, talc, and calcium carbonate play two roles. At first they were used mainly to extend the resin, or make it go further as they were inexpensive additives. The term filled usually refers to just that the material is filled; it is not chemically bonding to our polymer. We do get an increase in physical from use of extenders just not much.
 
It should also be stated that though material such as wood fiber are used as extenders they also impart higher physicals into the part and this would go for all extenders. It is just that if we were to use the same filler as in a reinforced grade its base component say glass fiber would be the same but the way it attached to the polymer would be different. It would form in its cold state what appeared to be one unit but there is no actual chemical bond to the polymer as in a reinforced classed grade. There is only a mechanical bond thus we could have different physicals. This is why when someone states the 30% glass filled material of manufacture A works better than that of B someone should investigate.
 
Improved Electrical properties
 
These additives typically carbon based, fibers, powders and or combination there of. These can be sized to impart higher physicals or not, and dependant of type used and amount will improve the conductivity of the material. There are new additives currently used which are chemical in nature, which are proving very successful. These can greatly enhance surface cosmetics and use of colorants in the parts. Carbon is black and the use of fibers or powder to enhance electrical is dependant on placing the particles on the surface, typically resulting in a bad or motley looking part surface.
 
With the use of carbon brittleness can be an issue dependant on the loading.
 
Moldings/ processing:
 
In general the following comments relate to all the above
1-     The use of an additive added to a base polymer will reduce the shrinkage of the base polymer. The higher the percentage used the more effect on shrinkage.
2-     The aspect ratio of the additive will have an effect on shrinkage. For example glass fiber which is thin and long may alien in molding or extrusion resulting in a different shrinkage flow versus cross flow.
3-     It is not uncommon to use two variations of fillers (glass fiber and beads or powder) so as to try and maintain a uniform shrinkage rate. (basically eliminate effect of #2)
4-     Particle shape is an important consideration, for example calcium carbonate and talc are sometimes stated to be equal or the same chemically, when in fact it is their shape which is important. Talc is flat irregular in shape while Calcium Carbonate is round. Talc will decrease impact and improve stiffness while Calcium Carbonate will not affect impact, and does not have as great an effect on stiffness as Talc in equal percentages.
5-     If the additive was not dried correctly prior to introduction to the polymer matrix, drying at the processor will not cure the defect. (splay, moisture)
6-     In most material the surface cosmetics will change with additional fillers, and to achieve a buried filler (part looks as if no filler in it) a higher mold temperature typically works.
7-     The use of fillers will increase stiffness allowing for removal of parts at greater temperatures than an unfilled polymer. Check the glass transition temperature.
8-     Weld line areas tend to be weaker in a filled material due to fillers at the joint. This sometimes leads to modification of the flow path, overflow tabs and other fixes to improve the intermingling of the flow front.
 
Comment:
 
In recent years the use of Nano Particles has been touted and reported on. These though small in size do aid in the stiffness and properties stated due to their extreme small scale and where they can mate to the polymer. I have not addressed these here.
 
It does bring up a point to size though, and this is something that everyone should be aware of, especially with on machine compounding and new technologies, knowing the particle size can help in troubleshooting and or solving an issue. It is somewhat like grinding up bad parts to reuse with virgin material, the fibers or fillers in the regrind are shorter or smaller the second time through, thus resulting in a variation in aspect ratio and final properties of our product.
 
 

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Silveys Plastic Consulting

360-882-3183

silveysplastics@aol.com,  silveysplastics@hotmail.com