DuPont MULTIBASE™ polydimethylsiloxane (PDMS) masterbatches, generally referred to as siloxane, are additives used for process improvement and surface modification. The term siloxane comes from the functional group of silicon and oxygen used in silicone polymers. These siloxane masterbatches contain 20-50% silicone with remainder of the formula being the carrier resin. The different series of MULTIBASE™ masterbatches have varying molecular weights of silicone and/or silicone with functional groups for a variety of process improvements or surface modifications.
PDMS, used in the siloxane masterbatches, have the following characteristics which make them useful as an additive:
- Low surface energy and tension: helpful for use as a lubricant, release agent, and for the silkier/smoother feel (see figure 1)
- Good heat stability: can be processed at the temperatures needed for the carrier polymer types
- Weather and water resistance: can slightly improve UV performance and is hydrophobic
- Low toxicity: can be used in flame retardant packages or materials while limiting toxic fumes that are given off
Figure 1: Surface energy of various polymers and PDMS
Historically siloxane in fluid form has been looked at for use as lubricants, but they are difficult to handle, have surface adhesion problems, and blooming/migration issues which have stopped their widespread use. The masterbatch solid form eliminates the issues experienced with siloxane fluids, they are easy to handle and have grades that can also be used in food contact applications. The siloxane domains in the masterbatches enrich the surface of the part without need for blooming or movement after the part is molded and solidified. Depending on the dosage used for siloxane, different improvements can be made:
- 0.2-1.0% will act as a process aide to lower pressures, help with release from the mold, and improve flow (see figure 2)
- 1-5% will start to affect the surface performance of the part
- 5-10% will show a larger reduction in coefficient of friction (COF) and affect the touch and feel of the part (see figure 3)
Figure 2: Graph showing roughly a 10cm increase in flow from using 0.4% siloxane masterbatch in a polypropylene homopolymer resin
Figure 3: COF improvement in both high density polyethylene and polypropylene
MULTIBASE™ siloxane masterbatches have many great uses as a processing aid, to help with extrudate quality, reduce coefficient of friction, or to simply improve the feel of the product.
The Chase Plastics team is here to provide insight into the many grades and variants of siloxane masterbatches available. Contact us today to see how our technical expertise, diverse product line, and outrageous customer service can help take your product from resin to reality! Whether you are looking for a particular part performance or a basic education, our sales and engineering teams are ready to answer any questions you may have.