Agilent Technologies The Effect of Analysis and Sample Preparation Conditions when Analyzing Ultra high molecular weight Polyolefins by High Temperature GPC Graham Cleaver graham.cleaver@agilent.com

1 October 1st 2014

Agilent – A Complete Portfolio of Instrumentation, Columns and Standards For GPC/SEC

2 October 1st 2014

Agilent Guides to Polymer Analysis

3 October 1st 2014

Introduction Polyolefins and Gel Permeation Chromatography (GPC)

4 October 1st 2014

•Gel permeation chromatography is a commonly used, important technique for characterizing polyolefins.

• Polyolefins are highly crystalline materials are difficult to analyse because aggressive solvent conditions and extremely high temperatures are required to maintain sample solubility.

• Careful selection of sample preparation techniques, analysis temperature and columns are of particular importance in order to avoid sample degradation and errors in reported molecular weights.

•This presentation looks at the effect of dissolution temperature, sample filtration and reduction of exposure to oxygen to significantly improve accuracy and reproducibility using GPC to characterize ultra high molecular weight polyethylene.

Acknowledgement : Dr Xiaowei Zhang is a analytical scientist at Kentucky, USA

Agilent GPC-220 High Temperature GPC Accurately controlled column oven with integrated injection system, columns and detector(s)

Temperature controlled solvent delivery module with solvent reservoirs

Dual temperature zone autosampler prevents sample degradation

High precision Agilent pump ensures reproducible results even in viscous solvents

Sample is heated from injection to waste to maintain sample solubility & stability

5 October 1st 2014

Methodology for GPC of Polyolefins

• Solvent selection is limited 1,2,4-trichlorobenzene (TCB) most commonly used

• Elevated temperature is required to achieve dissolution

Typically dilute polymer solutions (1-2 mg/ml) prepared at 135-160°C for 1-4 hours depending on molecular weight and crystallinity

• Selection of columns appropriate to the application

Molecular weight resolving range and efficiency of separation

• High temperature GPC system required to maintain all components at the analysis temperature

Typically polyolefins are analyzed at the dissolution temperature

6 October 1st 2014

Two Critical Stages Sample Preparation and Analysis

• High temperature is required to prepare and analyse the sample

• Both stages have a significant effect on the chromatography and results obtained

• A range of temperatures are employed for both stages which depend on user, laboratory protocol and equipment design

• The effect of different temperatures in these two stages is analysed and reported

• Ultra high molecular weight polyethylene (UHMWPE) samples were used in this study

• The samples were prepared at low concentration in the range 0.02-0.5 mg/ml

3 October 1st 2014

TCB

+

PE Solution

What Temperature?? How Long??

How long should the sample be

agitated for? Nitrogen purge?

Cap or uncapped vials? HEAT Is the polymer

truly in solution?

•Sample preparation of polyolefins is a critical part of their analysis

• Elevated temperatures are required to dissolve highly crystalline samples

• Long dissolution times and gentle agitation of the sample are required

N2 ?

3 October 1st 2014

Sample Preparation

PL-SP 260VS Sample Preparation System

9

Sample preparation was performed using the PL-SP 260VS sample preparation system

Designed to heat samples up to 260ºC

Can be used to filter at high temperature

System allows programmable variable speed agitation (shaking)

Inert gas purge when hood fitted

9 October 1st 2014

Shaker / Agitator

Thermostatted Sample Blocks

Hand Pipettor / filter

Temperature and Shaker Controls

10

DISPLACEMENT BUTTON

SLOT FOR FILTER CARTRIDGE

CLAMPING LEVER FILTER CARTRIDGE

Colour coded to indicate porosity

4 Frit/filters per cartridge

Clear centre hole for cleaning and for transfering samples without filtration

PL-SP 260VS Hand Pipettor

10 October 1st 2014

A. Sample unfiltered and transferred by pipettor B. Sample filtered through 1 µm glass fibre membrane C. Sample filtered through 2 µm Stainless Steel Frit D. Sample filtered through 0.5 µm Stainless Steel Frit gives high

resistance, and very little carbon is filtered out

A B C D

Filtering Carbon Filled PE

11 October 1st 2014

The PL-SP 260VS provides the best method for preparing and filtering samples at high temperature

Fillers or insoluble material never introduced to any part of system

Eliminates potential build up or blockages

The heater unit can house a large number of vials, both sample prep 20ml size and autosampler 2ml size, with a temperature range up to 260°C

Agitation via gentle shaking ensures samples are fully dispersed in solution without risk of degradation or shear

A custom built pipettor unit allows the filtration of samples at high temperature through either stainless steel or glass fibre filters with minimal user contact

PL-SP 260VS Sample Preparation System Summary

12 October 1st 2014

General Analysis Conditions Polyolefin GPC

• Solvent: Trichlorobenzene with BHT

• Column set: 3 x PLgel Olexis (300x7.5mm) / 20um Mixed A

• Injection volume: 200 μl

• Detector: differential refractive index, LS and Viscometer

• Oven temperature: 160ºC

•Sample preparation time: 3-7 hours (until completely dissolved)

• Sample preparation temperature: 160ºC, with N2

October 1st 2014 13

T2 T4

T1 T2 T4

T1 T1 T2 T4

1 2 3 4 5 6 7 8 9 10 11

14

The samples were monitored for complete solution by the measurement of stringiness observed in the sample when a heated glass rod was used to stir the sample and then lifted out of the sample

175 170 165 160 155 150 145

Sample Name Expected Mw Concentration mg/ml

T1 1.0M 0.4

T2 2.0M 0.2

T4 4.0M 0.05

N2

14 October 1st 2014

Sample Dissolution Temperatures

15 T2, 170°C

T1, 160°C, N2

15 October 1st 2014

Sample Dissolution Temperatures

October 8, 2014 Confidentiality Label

16

DRI

Viscometer

Light scattering detector

Triple Detection at Elevated Temperatures

The GPC system was calibrated with PL-Easical standards and then verified with PE standards; NBS1475 and a narrow PE standard of Mw=1.2Mg/mol

NBS1475 Mw Mn Run 1 53.2K 16.5K

Run 2 53.5K 15.5K

Run 3 52.0K 15.5K Certified

data 53.0K 18.3K

17 October 1st 2014

High Temperature Sample Analysis

Injection point Hot Zone Warm Zone

50

100

200

Tem

pera

ture

(C)

-20 -10 0 10 20 Vial Position

Carousel Motion

Injection Point

Agitated

Dual Zone Autosampler 40 vial position carousel 2 ml glass vials with crimped aluminum caps Sample can be slowly stirred prior to injection Two zone heating, minimized risk of sample degradation

PL-GPC 220 Autosampler

18 October 1st 2014

Oven To Injection Valve Injection system

Vial is transported up to the column oven Vial equilibration time in the oven is programmable Excess solution returned to vial No risk that the polymer will precipitate out of solution and cause a system blockage Injection precision RSD <1% with no cross contamination

19 October 1st 2014

PL-GPC 220 Autosampler

Hot

Cold

Columns

Pump

Injection System Electrically actuated injection valve Flushed fixed loop injection Interchangeable loop volume, 5 - 500 µl Loop and valve in oven Eliminates sample precipitation and blockages No contact between solvent and syringe

Avoids sample carryover and contamination of syringe Extends lifetime and reduces maintenance required

20 October 1st 2014

Minutes

5 8 11 14 17 20 23 26 29 32

dw/d

logM

logM

0.0

0.1

0.2

0.3

0.4

0.5

2 3 4 5 6 7

Overlaid raw data chromatograms

Overlaid molecular weight distributions

Repeatability of GPC (polyethylene) Injection

No. Mn Mw Peak Area

1 17,289 76,818 333851 2 16,988 77,434 335496 3 17,248 77,514 332616 4 17,251 77,052 335635 5 17,348 76,520 334212 6 17,487 77,728 333511 7 16,898 77,578 335642 8 17,457 77,288 334923

Mean 17,302 77,241 334485 s.d. 220 687 1048

% variance 1.3 0.5 0.3

21 October 1st 2014

Analysis of commercial polypropylene samples held in carousel for prolonged period of time Without dual zone heating, significant degradation of the sample can occur over extended periods in the autosampler By controlling the temperature profile, degradation can be minimised

PL-GPC 220 Autosampler Effect of Autosampler Temperature

22 October 1st 2014

23

The Effect of Carousel Holding Temperature

Chromatograms Above Below Hot Zone Temperature 160 °C 80 °C

Equilibration Time 2 mins 10 mins

23 October 1st 2014

• In this study of UHMWPE samples we can clearly see that the conditions of sample preparation is extremely important to achieve reliable results

• Sample preparation temperatures equal or greater than 160°C were required to dissolve the all the samples including the highest molecular weight samples

• Sample preparation times ranged from 3 to 7 hours to ensure complete polymer dissolution

• It is necessary to purge the sample preparation system with nitrogen gas to

eliminate oxygen and thus help prevent oxidative degradation during the sample preparation. The results show that when nitrogen is used the molecular weight integrity of the samples is maintained for a much longer time at temperature

• Long run times require the queuing samples to be exposed to high holding temperatures which can also cause degradation. Using lower holding temperature and longer oven equilibrium times can overcome this problem

24 October 1st 2014

Conclusions

Thanks For Your Attention

Any Questions

25 October 1st 2014