Custom Compounders Since 1973

Ask the Plastics Expert

Plastics Group has compiled a list of frequently asked questions that we believe will assist you in better understanding our products and processes. These represent some the issues most often encountered by our engineering and manufacturing staffs. If you have a specific question that you would like to ask, please use the form to submit your question. 

FYI - we will be awarding a piece of Plastics Group merchandise to the “best” question submitted by a site visitor each month.

Just a quick reminder that The Plastics Group of America, based in Woonsocket, RI, the manufacturer of the Polifil® line of reinforced resins, is still going strong, and should not be confused with The Plastics Group, Inc., a blow molding company which recently had to shut down facilities in Ohio and Illinois.


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Frequently Asked Questions

Q. Do you have any grades of material that are NSF approved?

A.  Yes, these grades have the WS designation at the end of the product description. They are available in White, Natural, and Black with 10, 20, 30, and 40% glass loadings. The listing is under TPG NSF/ANSI 61.

Q. Are any of your materials spec’d in or certified for Automotive Approval or use?

A.  While many Polifil grades may meet the requirements of certain Automotive specifications, they are not listed per se. When you encounter an Automotive specification, try to obtain a callout or copy of the specification. All the inquires regarding conformance to a specific Automotive callout should be referred to Technical Service.

Q. How does TPG adjust their prices for Polypropylene when the market moves up or down?

A.  TPG is (and has always been) sensitive to the market's price fluctuations and we try to reflect them in our pricing, continually striving to provide our customers with exceptional value when they're in the market for any PP product.

Q. What is the difference between Homopolymer PP vs. Copolymer PP?

A.  Copolymer PP has ethylene as a comonomer along with propylene. This polymerization method improves room temperature and low temperature impact strength and elongation. HDT and Tensile Strength will be lowered with the addition of ethylene as well.

Q. If an application/part will eventually be custom colored, is it ok to run parts in a natural for testing purposes?

A.  Yes, there will be a slight difference in mold shrinkage and physical properties, but it should give a good indication of suitability in the application.

Q. What is “bleaching?”

A.  Beaching refers to the loss of color intensity when color concentrate is added to filled feedstock. To counter this effect, you need to increase the percentage of  color concentrate added to the filled feedstock until you achieve the appropriate color match. This additional color concentrate can degrade the physical properties of your resin. The Plastics Group provides Free color blending and matching as part of its regular compounding services removing the worry about any of these negative side effects associated with achieving a proper color match. 

Q. What is a “UV” stabilizer?

A.  UV, Ultraviolet Radiation is a result of exposure to strong or direct sunlight. Over a prolonged time UV exposure will cause a loss of physical properties and appearance in the resin. A UV stabilizer or inhibitor will protect the resin and are essential for end products located in strong or direct sunlight. The Plastics Group can custom-compound and formulate all its resin products with a UV-package specific to your application to protect the resins physical properties and appearance. 

Q. What advantages does TPG’s ISO certification offer its customers?

A.  For one, some companies require their suppliers to have a registered quality program such as ISO to do business. TPG has been an ISO Certified company since 1996 and developed stringent Quality Systems that guarantee we can supply you with the very best products and services at the most competitive pricing available. TPG’s entire ISO certification program is geared towards meeting specific customer requirements and needs. For example, Polifil® product quality is directly based on customer specifications and requirements. This information is used to develop a specific customer profile for each Polifil® product ordered. This customer profile is cross-referenced each time a customer places an order, thus ensuring product integrity and continuity for lot-to-lot consistency. Simply stated, TPG’s ISO certification is another demonstration of the company’s commitment when it comes to meeting its customers’ needs.

Q. What is a Living Hinge?

A.  A Living hinge is thin sections of plastic that connect two segments of a part to keep them together and allow the part to be opened and closed. Polypropylene Homopolymer and copolymers have exemplary capability as a living hinge.

Q. Can Polypropylene be milled and shaped?

A.  Polypropylene can be milled or shaped readily on standard machine shop tools. A good finish can be produced in either operation. Burr formations are not a problem since they can be removed easily.

Q. Will glass-filled materials rapidly wear out molds and molding machines?

A.  Once the resin is melted; the wear is not much higher than for mineral-filled materials. However, wear will be higher in material handling systems where pellets abrade the lines and hoppers. Thicker transfer lines and gentle radii on all bends will minimize this issue.

Q. Will glass-filled regrind from sprues, runners and bad parts ruin the properties of the parts?

A.  While regrind materials will have slightly lower properties; the molder can normally recycle all of the regrind if certain steps are taken. Regrind should be added back in evenly throughout the run, and, molds should be designed with no more than 20% of the weight in sprues and runners.

Q. Does Melt Flow of Polypropylene affect the properties?

A.  Over much of the melt flow range of polypropylene, there is a surprisingly little effect on mechanical properties. Most properties will decline slightly as melt flows become higher. About 35 melt flow and above, the material becomes more brittle and losses in tensile properties become more substantial. Higher flow PP will take less injection pressure to fill a mold. However, the material will flash more easily, and high flow materials sometimes suffer from flow marks due to “jetting," or squirting into the mold too rapidly.

Fractional melt flow PP will have noticeably higher impact properties. PP shear thins quite a bit, so it is often possible to fill even large molds using single-digit melt flow resins. Fractional melt flow PP is rarely injected.

Warp is not directly affected by melt flow. The general molding conditions, degree of mold filling, mold packing, and cooling will have a much greater effect on warp than the resin melt flow.