There are hundreds of resins and thousands of formulated or compounded grades of various plastic materials on the market. Knowing the type of material is very critical in decision making. Without knowing the type of material, one cannot decide on part design, tool design, processing conditions, post processing treatments, and most importantly cost. Almost half of all the part failure (45%) occurs due to poor material selection. Designers must choose materials carefully.
We routinely get requests from distributors, molders and convertors, who often buy materials from secondary sources or are interested in making products or compounds similar to ones in the market. We also get requests from product manufacturers who buy finished components from overseas vendors. These are most often when manufactures experience difficulties in processing or are looking for alternative materials. They want to know or confirm the type of resin.
Not using the right material for the application can cause huge problems downstream.
Some example questions are:
- Is this HDPE, LDPE, LLDPE?
- Is this PP homopolymer or copolymer? What is the C2 content?
- Is this part made of Nylon 6 or Nylon 66?
- Is this recycled (or degraded) or virgin material?
- Is this GPPS or HIPS?
- What is the approximate amount of PC in the PC/ABS blend?
- Is this flexible material PVC? What is the type of plasticizer? How much?
- Are these components made from glass filled Acetal or Nylon?
The primary objective of material identification is to determine the type of resin; it is not a quantitative composition analysis.
There are many unique ways to identify type of resins and additives. We use following tests:
- Physical appearance and feel: Is the part clear or opaque, solid or cellular, rigid or elastomeric?
- Is it flammable or flame resistance? Is there smoke or odor when the part burns? What is the color of smoke? –Flame test
- What is the density of the material? – Densimeter
- Is the material filled or unfilled? Ash test
From these tests one can narrow the list of possibilities. For example, flexible LDPE burns like a candle with flaming drips, whereas PVC self-extinguishes. Both PVC and Nylon self-extinguish, however, PVC burns without flaming drips, whereas Nylon does exhibit flaming drips. GPPS is clear but HIPS is opaque. If the density is greater than the expected density for unfilled resin, there may be some fillers or reinforcements.
Sometimes further tests are required.
- FTIR or ATR on either part pellet surface or on melt pressed film helps to identify the class of material, whether or not it is a blend, or if there are plasticizer or process stabilizers. However, FTIR would not be able to detect very low level (ppm) additives and only provides qualitative analysis. Being dependent on functional groups only, it will not be able to distinguish between similar materials, e.g. Nylon 6 and Nylon 66 or PET and PBT.
- DSC – When the general class of material is identified using the above methods, DSC can further distinguish between sub-classes based on differences in melting point and glass transition temperatures. e.g. Nylon 6 vs. Nylon 66, PET and PBT. This can also help to determine the amount of major components within blends and alloys.
- TGA- Once the material is identified, TGA can be used to identify the amount and type of major additives (plasticizer, oils, F R) or determine the amount of inorganic filler or CB.