ANTIOXIDANTS
...used to prevent thermal degradation
...inhibit ‘oxidation’ (i.e. degradation)
…are ‘cheap’ insurance for multiple pass materials
Antioxidants are generally divided into primary and secondary categories. Each
category has a specific function in polymer stabilization.
Primary – used to protect the finished product. This type of stabilization ensures
performance over the life of the finished good. Typical chemistry used is
phenolic-based.
Secondary – used as a process stabilizer. Effective way to protect the polymer
during processing, especially when the polymer undergoes multiple heat histories.
Typical chemistries employed include phosphites or thioesters.
Primary/Secondary Combination – Both primary and secondary antioxidants
are often used in a combination. In this way, the polymer is protected both during
the processing step and throughout its service life.
Effective Temperatures for Stabilizers
Long Term Thermal
(No Melt Processing)
Hindered Amine
Long Term Thermal
Melt Processing
Long Term Thermal
(No Melt Processing)
Hindered Phenol
Thiosyn.
(&Phenol)
Phosphite
Hydroxylamine
Lactone
Vitamin E
(No Long Term Thermal)
0
50
0
100
0
Melt Processing
150
200
Temperature (°C)
250
300
THERMO-OXIDATIVE DEGRADATION
On the molecular level, oxidation occurs in the following manner:
Polymer
R.
RH
Oxygen
RO.+HO.
ROO.
RH
R.
+
ROOH
It is up to the antioxidant stabilizers to break the cycle and assure that the performance
of the polymer is maintained. At the end of this document, references are made to
specific Ampacet products that are effective in breaking the oxidation cycle.
NON-YELLOWING ANTIOXIDANT CONCENTRATES
Phenolic discoloration can result from many conditions, including over-oxidation of
hindered phenol antioxidants, pigment interaction (e.g. various grades of TiO2 ) with
phenols, ‘cardboard yellowing’, and ‘gas fading’ due to the presence of NOx gases (e.g.
fork lift or gas heater fumes).
Two products are offered by Ampacet to help alleviate discoloration (yellowing or
‘pinking’) which can occur with conventional phenolic antioxidant systems due to the
conditions mentioned above. Products 101124 and 101125 are phenol-free and not
onlydo not contribute to yellowing due to phenolic over-oxidation, but also help prevent
discoloration when yellowing may occur from other ingredients in the polyolefin
processor’s formula.
Both 101124 and 101125 are based in an 8 MI LDPE carrier resin (low gel, extrusion
coating grade.) Product 101125 contains stearate, as the addition of stearates has
been shown to lessen the formation of yellow species. For applications which cannot
tolerate the addition of stearates,stearate-free 101124 should be considered.
Studies performed by Ampacet have shown these phenol-free, Ampacet-proprietary
mixtures are effective at minimizing or eliminating discoloration commonly associated
with over-oxidation of phenolic antioxidants. Experimental work involving bot oven
aging at 60°C and gas fade testing were carried out using molded low density
polyethylene plaques containing 5% of a rutile grade of TiO2 (known to aid in promoting
discoloration) as a control, as well as in combination with 1000 ppm of a traditional
phenol/phosphite antioxidant package. 2.5% of 101124 and 101125 (yielding 1000 ppm
active) were then each added for determining discoloration tendencies.
The attached graphs illustrate the benefits of 101124 (and 101125) over conventional
phenolic-based antioxidant systems with respect to yellowing tendencies.
The
traditional phenolic antioxidant system is shown to actually contribute to yellowing which
is illustrated by the higher yellowness index values over the control plaque which
contains no antioxidant package. The addition of 2.5% 101124 or 101125 significantly
decreased yellowing tendencies even in the presence of 5% of a grade of TiO2 known
to enhance discoloration.
Oven Aging Analysis
oven aged at 60 C
delta Yellowness Index
molded LDPE plaques with 5% uncoated TiO2
4
No Antioxidant
1000 ppm Traditional Phenolic AO system
2.5% 101124 (1000 ppm AO package)
delta Yellowness Index
3
2
1
0
-5
0
5
10
15
20
Time (days)
25
30
35
40
Gas Fade Analysis
delta Yellowness Index
molded LDPE plaques with 5% uncoated TiO2
25
delta Yellowness Index
20
15
No Antioxidant
1000 ppm Traditional Phenolic AO system
2.5% 101124 (1000 ppm AO package)
10
5
0
-5
-10
0
10
20
30
Cycles
40
50
60
AMPACET ANTIOXIDANT PRODUCTS
The following list provides general information and usage guidelines for Ampacet
antioxidant masterbatches. Specific antioxidants can be developed to meet special needs
where required.
101124 -
Phenol-free process stabilizer for minimal discoloration. Can also help
minimize discoloration due to additives present in your letdown resin.
101125 -
Version of 101124 with additional zinc salts for the most potent anti-coloring
stabilizer properties. Should not be used where stearates are a concern.
100401 -
Cost effective process stabilizer rich in secondary phosphite for preventing gel
formation. Good for flooding extruder during “down times” to prevent
excessive ‘black specking’ upon restart.
10886 -
Blended primary/secondary AO for high heat processes where the finished
part needs good long-term outdoor life.
100307 -
Blended phenol/phosphite for maximum outdoor durability.
100363 -
Vitamin E masterbatch - provides outstanding melt processability (helps
minimize gel formation). Best when used in combination with one of the
above products.
For more information, please contact Ampacet’s technical support team at 888-822-7546 or 812-466-9828.
Disclaimer: The information and recommendations contained in this document are based upon data collected by Ampacet and believed
to be correct. However, no warranty of fitness for use or any other guarantees or warranty of any kind, expressed or implied, is made to
the information contained herein, and Ampacet assumes no responsibility for the result of the use of the products and processes
described herein. This is an uncontrolled document and information may be out of date.