Precipitated Silica for High-Performance Footwear Rubber Reinforcement
During World War II, supplies of natural rubber to the U.S. were cut off, forcing many companies to seek out new raw material solutions for their rubber-based products. Footwear manufacturers, whose industry was among the most greatly affected, responded to the shortage by reinforcing shoe soles with carbon black.
When the U.S. Navy began to complain that carbon-black soles were leaving dark marks on their ship decks and housewives began to see the same damage to their living room floors, an enterprising rubber company turned to PPG for an answer.
Together, we combined a new synthetic elastomer with PPG SILENE™ precipitated silica, a product that we had developed primarily for the tire industry. The result was more than a new leather-like-sole with improved wear resistance that didn’t leave scuffs on floors; it also marked the beginning of PPG’s leadership in engineering advanced reinforcing silica products for the footwear industry.
Today, that same spirit of innovation drives the development of our PPG HI-SIL® non-black reinforcing fillers. Available in a variety of grades, this diverse set of precipitated silica grades enables high-performance footwear formulators to produce colored or translucent non-marking soles with superior durability and resilience, along with improved compounding stiffness and modulus for enhanced flexibility and comfort.
Other benefits of Hi-Sil and Silene reinforcing silica products for footwear include:
- Good color and transparency for translucent soling
- Enhanced abrasion resistance in colored heels and soles
- Better flex/crack growth resistance and hot-tear resistance
Recommended Silica for Footwear
Typical Properties
| Silica Grades | N2 (BET-5) Surface Area (m2/g) |
pH | Residual Salt Type | Physical Form | Reinforcement |
|---|---|---|---|---|---|
| Silene 732D | 33 | 8.5 | Na2SO4 | Powder | Semi-Reinforcing |
| Hi-Sil 532EP | 55 | 8 | Na2SO4 | Powder | Semi-Reinforcing |
| Hi-Sil 233 | 135 | 7 | NaCl | Powder | Reinforcing |
| Hi-Sil 210 | 135 | 7 | NaCl | Pellet | Reinforcing |
| Hi-Sil 243LD | 135 | 7 | NaCl | Granule | Reinforcing |
| Hi-Sil 233-D | 151 | 7 | Na2SO4 | Powder, Granule | Reinforcing |
| Hi-Sil 255G | N/A | 6.3 | Na2SO4 | Powder, Granule | High |
Silene is a trademark and Hi-Sil is a registered trademark of PPG Industries Ohio, Inc.