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Ask Mr. PlasticMr. Plastic is ready to answer all your technical plastic questions

Dynalab Corp.'s Design and Manufacturing Engineer is available to answer your plastics questions via e-mail. Sorry, phone calls can not be accepted as he is very busy managing our plastic fabrication facility.

Below are some examples of the hundreds of questions Mr. Plastic has answered over the past years from around the world! This free service is offered by Dynalab Corp. in addition to the extensive plastic materials web pages already on our site.

Chemical Properties A-F  Physical Properties of Plastic Plastic Materials
Chemical Properties G-Z Use and Care of Plastics Custom Fabrication

Q. How long before standard acrylic yellows and degrades in an outdoor application (solar heating panels)?
A. Clear acrylic is naturally resistant (not impervious) to attack from UV light. A panel should last many years before showing signs of attack from UV rays. Just a bit of information for you...I read that acrylic monomer is sometimes blended with other resins to retard breakdown from UV attack; it was added to polyester greenhouse panels and that extended their life by about 5 years.

Q. Is it possible to weld HDPE? I am about to start a design to line a catcher chute with this material and welding would very much simplify the design.
A. HDPE welds very nicely. In fact welding is the preferred method of joining HDPE.

Q. I was wondering how good is the chemical resistance of PC to silicon.  Also how well does PC ultrasonically weld during far field welding?
A. Silicon(Si) is commonly used as a coating for polycarbonate to make it scratch resistant. Since Polycarb is Amorphous with little or no crystalline structure it should be well suited for ultrasonic welding. Also, since it is rigid Far-Field welding should be fine.

Q. Is PETG as clear as Acrylic and can it be as thin as acrylic? Well the application I am using it for is to stitch acrylic to leather, I wanted to see if it can be used rather than using PVC.  Unfortunately, I am not sure of a good method to do this, and have not been able to find anyone that has done this?
A. Yes PETG is clear and available in thinner gauges and so is Polycarbonate. I’m sure your project is feasible, it’s simply a matter of finding the right combination of materials and the proper equipment to do the job.

Q. I am trying to design a small plastic part that will be used outside.  I originally wanted to use PP until I read on your website that PP has a minimum temperature of 32°F or so.  Would nylon be a better choice for outside use?  I have been told that I could also use engineered PP but I do not even know what that is.  This part needs to be slightly flexible but not get brittle in the cold.  Do you have any advice?
A. It sounds like High Density Polyethylene (HDPE) would work well for you. It has a better low temperature range than PP and won’t get brittle under normal use. Also, be sure to use black material because it won’t degrade due to UV light exposure.

Q. Please can you tell me the compatibility of acrylic and acetyl with nucleic acids. Under high salt buffer conditions (i.e. as in lysis solution) will these materials be likely to adsorb nucleic acid.
A. Both Acrylic and Acetal are hygroscopic plastics, meaning they will absorb and store moisture. However, there is a lot of laboratory equipment made from Acrylic that comes in contact with Nucleic Acid molecules on a daily basis with no ill effects. I can’t cite a reference for you but I believe a little web surfing by you may turn up a compatibility table that shows Acrylic to be completely safe…and maybe Acetal as well.

Q. I am looking to build some 1 gallon tanks which must contain water for a period of 10 years or more and be exposed to exterior sunlight as well. We have prototyped in acrylic but have found some water loss over time, we believe due to the moisture permeability. Any other plastics you might try, or materials to line the tank with?
A. The first thing that comes to mind is Polyethylene Terepthalate (PET). This is a very common resin used in the packaging industry to contain liquids, including those under pressure from carbonation. Another possibility would be a barrier grade of Nylon, although you may require a specialty UV stabilized grade.

Q. I am trying to determine which plastics are considered "combustible." I am not sure how that would generally be measured, but I don't think "melting" temperature is the same thing. The government standard for a combustible solid is one that has a burn rate of >2.2mm/second. If that's the standard, which plastics are "combustible?
A. You will probably want to reference Underwriters Laboratories flammability data for this information. “UL 94” is a classification for flammability of plastic materials based on burning tests. The ratings are 94V-0, 94V-1, 94V-2, 94HB, 94VTM-0, 94VTM-1, 94VTM-2, 94HF-1, 94HF-2, and 94HBF. These ratings correspond to burn rate, burn direction, and ignition.