Solid Phase Extraction for Additive Analysis in Polyolefins Dr. Robert Brüll Fraunhofer Institute for Structural Durability and System Reliability LBF Darmstadt, Germany

Stabilizers in polymers

Table of contents Introduction State of the art Stabilizers (Phenolic antioxidants, UV absorbers and HALS) PGC – stationary phase Separation of polymer additives using PGC Separation of phenolic antioxidants Separation of UV absorbers Separation of HA(L)S SPE – solid phase extraction Separation of polyolefins and polymer additives using silica Resume

Lifetime of polymer materials Aging of the polymer material caused by: External factors (Processing, temperature, humidity, UV-light, pollution, radiation) Internal factors (Migration, agglomeration, post-crystallization)

‘All polymers are aging… ... the time scale may be different’ 2 ROO∙ O2 RH 1 Polymer R∙ R∙ ROOH H2O 3 RO∙ HO∙ ROH Initiation reaction caused by UV-light Accelerated degradation reactions Termination reactions

And: the conditions of ageing matter! Multifactorial long-term behavior is typically observed in complex systems like polymers or macromolecules, e. g. proteins.

Mechanisms inhibiting degradation Protection through: UV absorbers Phenolic antioxidants HALS 1 3 2

Failure may occur, but we need to know how we can do better!!

Analysis of stabilizers - state of the art OIT measurements IR spectroscopy Precipitation of the polymer in solution Soxhlet extraction Supercritical Fluid Extraction (SFE) Soxhlet: Ausbeute/Wiedergewinnung 97% für gemahlenes Polymer Firma intertek Schweiz bietet diese Leistung an - Identifizierung von Polymeradditiven OIT-Messung für Stabilisatorgehaltbestimmung von Polyolefinen (Einschränkung durch Vorhandensein von Füllstoffen, Pigmenten, Verarbeitungsstabilisatoren) IR-Spektroskopie (Individuelle Kalibration für jede Polymer/Stabilisator-Kombination) Ausfällen des Polymers in Lösung (bei Polyolefinen nicht möglich, da diese erst bei hohen Temperaturen löslich sind) Soxhlet-Extraktion (Teilweise erschwerte Extraktion, Extraktionsrate 6 bis 48 h) Superkritische Flüsskeitsextraktion (sehr effektive Methode mit meist CO2 als Extraktionsmittel, Wiedergewinnung ca. 90-95%; niedermolekulare Fraktionen können erneut herausgelöst werden)

Goal Analytical approach to determine (modern) stabilizers in polyolefins Criteria Improved selectivity with regard to chemically similar structures Precise quantification of a wide range of stabilizers Fast and robust Separation of high MW additives from the matrix

PGC – Porous graphitic carbon Hypercarb® sp2-hybridized ring carbons (hexagonal order/ configuration) Stable (even at higher temperatures or flows) Porosity: ca. 75% Homogeneous surface Resistent against strong solvents Adsorption and desorption of polyolefins and stabilizers HPLC column Hypercarb (100 x 4.6 mm)

Separation of phenolic antioxidants AO7 Separation of phenolic antioxidants AO5 AO6 AO2 Overlay of normalized chromatograms of phenolic antioxidants. Gradient: MTBE→CHCl3. 30 °C Selective separations possible!

Separation of UV absorbers and HALS using Hypercarb® 2x UV1 Normalized chromatograms of UV stabilizers and low molecular weight HALS (Tinuvin 144 and Tinuvin 770). Gradient: MTBE→CHCl3 30°C

Separation of UV absorbers and HALS using Hypercarb® Low MW HALS elute before UV absorbers. Thus benzotriazoles (BTA) interact stronger with PGC than the tetramethylpiperidines (TMP). Phenolic antioxidants: Longer alkyl chains lead to stronger interaction with PGC (AO2 and AO6) The more aromatic the structure of the molecules the stronger the interaction with PGC (AO7) UV absorbers: Alkyl chain leads to stronger interaction (UV3) Cl atom leads to stronger interaction with PGC increasing the electron denisty in the BTA unit (UV4) Two UV absorbing units (UV5) lead to the strongest interation with PGC

Separation of HALS oligomers using Hypercarb® Overlay of normalized chromatograms of HALS oligomers. Gradient: 1-hexanol→n-decane 50 °C Chimassorb 2020/SABO STAB UV 40: 2600-3400 g/mol Chimassorb 944: 2000-3100 g/mol Uvinul 5050: 3000-4000 g/mol ADK STAB LA-63P unterscheidet sich deutlich von den anderen oligomeren HALS durch Spirozyklus in der Wiederholungseinheit

Chromatographic results using PGC as stationary phase Separation of HALS oligomers using porous graphitic carbon (PGC) as stationary phase PGC shows new selectivities in relation to these additives Separation and quantification of different stabilizers in a one-shot approach HPLC column Hypercarb (100 x 4.6 mm)

Solid Phase Extraction 1 Loading 2 Desorption SPE cartridge 1 2 Desorption Additive Desorption Polymer Problematik Polyolefine: Löslichkeit erst bei hohen Temperaturen (ca. 120-150 °C, abhängig vom Lösungsmittel) Polymer Desorption Polymer Desorption Additive  Additives Polymer removed Additives removed

Work Flow Oxygen sensitivity of polymer additives Approach: Flooding the system with inert gas Controlling the reproducibility and the extent of the error Verification of the received results with a well-known method (Soxhlet extraction) Konstruktion einer SPE, mit einer beheizbaren Einheit und Betreiben der SPE bei Temperaturen von ca. 120 °C Hohe Temperaturen beeinflussen das oxidationsempfindliche Verhalten Fluten des Systems mit Stickstoff bzw. Argon und Vergleich mit Ergebnissen bei Raumbedingungen Prüfung der Reproduzierbarkeit und Ausmaß des Fehlers (Grundgedanke ist Anwendungsbereich in der Industrie)

Device for High Temperature SPE Pump

Workflow Injection of polyolefins in n-decane at high temperatures (120 °C) in silica column No adsorption of polyolefins Injection of stabilizers in n-decane at high temperatures (120 °C) in silica column Adsorption of stabilizers Injection of stabilizers in CHCl3 at room temperature (30 °C) in silica column Desorption of stabilizers

Polymer-additive-solution Separation of additives from polyolefins using silica as stationary phase n-decane THF CHCl3 120 °C Polymer-additive-solution Desorption Polyolefins Desorption Additives Trennung PE/PP von Additiven mit Hypercarb nicht möglich: Additive und Polyolefine desorbieren bei hohen Temperaturen von Hypercarb (lediglich DCB und TCB kommen als Lösungsmittel in Frage, da für PE und PP mit Hypercarb desorbierend wirken) Polyolefine desorbieren von Silica-Säule und Additive adsorbieren bei 120 °C von Decan Additive können mit THF von n-Decan desorbiert werden THF kann diese Additive von Silica nicht desorbieren, starke Wechselwirkung der polymeren Additive mit der stationären Phase Silica-Material ist bei hohen Temperaturen stabil (Reproduzierbarkeit!)  Separation of polyolefins and additives using silica is possible

Recovery using UV detection Injection Column UV detection II Injection Capillary I Additive samples are injected in the silica column using different concentrations II Additive samples are injected directly in the capillary AO7 R2=0,9847 CHCl3; UV Detektion; 50 µl Inertsil WP 300 Ascentis™ Si, Column 5 µm ø Concentration [mg/mL] 0,2 0,8 1,2 AO1 1,00 0,99 AO5 0,89 0,90 AO6 1,01 AO7 Additives desorb nearly completely from silica!

Transfer of HPLC results to SPE SPE results correlate with the chromatographic results Gradient: MTBE→CHCl3 30 °C

Resume PGC enables the separation as well as the quantitative characterization of UV absorbers, phenolic antioxidants and low molecular weight HALS using gradient MTBE→CHCl3 and HALS oligomers using gradient 1-hexanol→n-decane PGC as stationary phase does not enable the separation of polyolefins and stablizers Silica as stationary phase enables the separation of different polyolefins and stabilizers desorbing polyolefins at high temperatures in a first step and then the additives at room temperature The chromatographic measurements using porous graphitic carbon as stationary phase prove the desorption of the additives

Thank you for your attention!

UV absorbers and low molecular weight HALS

AO1 AO2 AO3 AO4 AO5 AO6 AO7