Photo-Graftable UV Absorber Gets the Yellow Out

Sanduvor PR-25, a uv absorber based on new photo-reactive chemistry, was aimed primarily at coatings when it was first launched a couple of years ago. Since then it has made headway in clear plastics, including flexible PVC, polycarbonate, PET, and other engineering thermoplastics.

Made by Clariant Corp., Charlotte, N.C., Sanduvor PR-25 is a non-staining, highly absorptive, photo-graftable stabilizer based on benzylidene malonate ester chemistry. It boasts much lower color development than traditional hydroxy-substituted benzophenones and benzotriazoles. It is said to have three times higher absorptivity than these uv absorbers and to also outperform hydroxyphenyltriazines. The latter represent another relatively new uv-absorber chemistry that is now available from a number of suppliers, including Ciba Specialty Chemicals, Tarrytown, N.Y., and Cytec Industries, West Patterson, N.J.

Keeps the yellow out

Clariant's product-development technical manager for additives, Joseph Webster, says PR-25 has a maximum uv absorptivity at least twice as high as that of hydroxy-substituted triazines and three times as great as traditional benzotriazoles and benzophenones.

Clariant initially introduced photoreactive chemistry in the form of Sanduvor PR31, a low-molecular-weight, methylated, monomeric HALS. Sanduvor PR25 has the same backbone chemistry as Sanduvor PR-31, minus the HALS (piperidine) functionality. Like PR-31, PR-25 remains mobile within the polymer until it becomes permanently grafted into place under the influence of light. PR25 is a white crystalline powder with a melting point of 131-134 F.

The four accompanying graphs show the performance of PR-25 in retarding color development compared with traditional uv absorbers or the newer triazines. Data on transparent, compression molded flexible PVC shows PR-25 to outperform Ciba's Tinuvin P benzotriazole, traditionally a workhorse for flexible PVC, after 3000 hr of accelerated weathering.

Similarly, data on injection molded polycarbonate show less color development with PR-25 after 700 hr of accelerated weathering than with either Ciba's Tinuvin 234 benzotriazole (a workhorse for polycarbonate) or Cyasorb HPT 1164 triazine from Cytec.

In molded PET, PR-25 also produces less yellowing before weathering than does Tinuvin 234 (commonly used in PET). The unweathered PR-25 sample is virtually indistinguishable from the control sample containing no uv stabilizer.

More interesting is color development in PET after 600 hr of accelerated weathering where PR-25 still outperforms Tinuvin 234 benzotriazole.

Sanduvor PR-25 uv absorber is priced competitively with the benzotriazoles and newer triazines. It lists at $15.50/lb as compared with $14-28/lb for hydroxy-substituted benzotriazoles and $26-50/lb for the phenyltriazines.

Related Content

How2Recycle Label Changing Recycling Habits

The How2Recycle Label program finished its soft launch in early 2012 and now has more than 60 participating companies and brands and is growing every month.