Hyphenated Techniques in Polymer Characterization - American

thermogravimetric analysis (TG), differential scanning calorimetry. (DSC), dynamic ... The use of a simultaneous thermal analyser (STA) which is usual...
2 downloads 0 Views 1MB Size
Chapter 7

Polymer and Other Degradation Studies Using Thermal Analysis Techniques 1

2,3

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 26, 2015 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1994-0581.ch007

John P. Redfern and Jay Powell 1

Rheometric Scientific (formerly Polymer Laboratories Ltd.) Thermal Sciences Division, Surrey Business Park, Kiln Lane, KT17 1JF Epsom, England Bio-Rad, Digilab Division, 237 Putnam Avenue, Cambridge, MA 02139 2

Polymer characterisation, stabilisation and degradation are very widely studied by Thermal Analysis (TA). Single techniques, such as thermogravimetric analysis (TG), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and dielectric thermal analysis (DETA) provide important information on the thermal behaviour of materials. However, to obtain a more complete profile of, say, polymer degradation gas analysis is required, particularly since all of the techniques listed give mainly physical information on the behaviour of materials. The use of a simultaneous thermal analyser (STA) which is usually a combined simultaneous measurement of weight and energy usually referred to as a TG-DSC instrument) coupled to a mass spectrometer or to an FTIR provides a very powerful system for such studies. Key elements of the design will be stressed - underlining the importance of the interface system and the advantages of a comprehensive software package. A number of specific studies are discussed in some detail and reference is made to other studies. To say that plastics impacts all our lives is to state the obvious. The plastics industry is big business - a $150 - 180bn dollar business (equivalent to the Gross Domestic Product of a country like Switzerland) and growing worldwide both through increased usage in more and more countries and through new applications. The major end uses are shown in Table 1. There is also growing concern about disposal of used plastics and of the impact on the environment. There is, therefore, a clearly identified need for reliable methods to study the stabilisation and characterisation of these materials, to obtain knowledge on their properties and behaviour, the effects of modifying structure, additives and processes to produce the most appropriate, cost effective material for a specific requirement. The study of the degradation behaviour 3

Corresponding author 0097-6156/94/0581-0081$08.36Α) © 1994 American Chemical Society In Hyphenated Techniques in Polymer Characterization; Provder, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

82

H Y P H E N A T E D TECHNIQUES IN P O L Y M E R CHARACTERIZATION

TABLE 1 Major End-Uses for Plastics Packaging Construction Electrical and Electronic Industries Automotive Industry Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 26, 2015 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1994-0581.ch007

Annual World Sales of $150-180 bn TABLE 2a Thermoplastics

Thermosets

Melting Crystallisation Glass Transition (TJ

Curing Reactions

Expansion and Shrinkage Softening Strength Heat Capacity Thermal Conductivity Solvent and Water Retention

|

TABLE 2b Thermoplastics and Thermosets Ageing Thermal Stability Thermal Degradation Chemical Degradation is also important to contribute to our understanding of three possible decomposition scenarios, namely, in normal usage at operating temperatures, upon disposal or in accidental occurrences, for example in a fire. Therefore, there is a need to study the effects of ageing, the thermal stability, the degradation processes and the products of decomposition under a wide range of conditions. The techniques of thermal analysis are very significant to the wholefieldof polymers in that they provide essential information relating both to their characterisation and their degradation. Table 2a lists areas where Thermal Analysis (TA) provides information for characterisation while Table 2b lists areas where TA provides information on the degradation processes. TA techniques are a group of techniques in which the property of a sample is monitored against time or temperature while the temperature of the sample, in a specified atmosphere, is programmed. This programme may involve heating or cooling at a fixed rate of temperature change, or holding the temperature constant, or any sequence of these. The principal techniques are listed in Table 3. Of these the In Hyphenated Techniques in Polymer Characterization; Provder, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 26, 2015 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1994-0581.ch007

7.

REDFERN & POWELL

Degradation Studies Using TGA

83

most useful in the study of the degradation process are TG, DSC, Simultaneous Thermal Analysis or STA (a combined simultaneous thermobalance with a DSC measuring head incorporated, abbreviated as TG-DSC), STA-MS (a TG-DSC instrument coupled with a mass spectrometer) and a TG-FTIR or STA-FUR ( a thermobalance or a STA linked with an FTIR spectrometer). This review is limited primarily with the application of STA, STA-MS and STA-FTIR to the degradation of polymers and other materials. STA provides a precise simultaneous understanding of the physical phenomena of weight and energy change. The STA coupled to a mass spectrometer or to an FTIR instrument gives a more complete profile of the degradation process.

TABLE COMMON

TECHNIQUE

THERMAL

3

ANALYSIS

TECHNIQUES

ABBREVIATION

MONITORS

SINGLE TECHNIQUES

Thermogravimetry (Thermogravimetric Analysis)

TG

Mass

Differential Scanning Calorimetry

DSC

Energy

Differential Thermal Analysis

DTA

Temperature Difference

Thermomechanical Analysis

TMA

Dimensions

Dynamic Mechanical Thermal Analysis (Dynamic Thermal Analysis)

DMTA

Response to Oscillatory Load

Dielectric Thermal Analysis

DETA

Response to Alternating Current

Evolved Gas Analysis

EGA

Nature and/or Amount of Volatiles

Temperature Programmed Reduction

TPR

Solid-Reducing Gas Interaction

Thermogravimetry-Differential Scanning Calorimetry

TG-DSC

Mass and Energy

+ Mass Spectrometry

TG-DSC-MS

Mass, Energy & Gas Analysis

+ FTIR Spectroscopy

TG-DSC-FTIR

Mass. Energy & Gas Identification

DMA

SIMULTANEOUS TECHNIQUES

In Hyphenated Techniques in Polymer Characterization; Provder, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

84

HYPHENATED TECHNIQUES IN POLYMER CHARACTERIZATION

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 26, 2015 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1994-0581.ch007

Instrumentation A. Simultaneous Thermal Analyser (TG-DSQ. The instrumentation for STA is shown schematically in Fig. 1. The advantage of single sample simultaneous experiments have been discussed previously (i, 2). It is appropriate to summarise these advantages: 1 Removes uncertainty - a) precise correlation of events occurring on both TG and DSC assured, b) removes any problems relating to sample inhomogeneity or batch variations. 2 Gives fuller characterisation - ensures greater certainty in identifying thermal events. 3 Validates quantitative measurements from DSC for phase changes, melting and purity measurements. 4 Detects moisture content enabling in-situ dry starting weight to be known accurately. 5 Accurate TG temperature calibration using DSC/DTA standard materials.

M

G

GAS

IN

GAS OUT

Schematic diagram of simultaneous thermal analyser furnace and head. A, Ceramic tube to protect hangdown; B, movable baffle plates with gas ports; C, sample and reference crucibles; D, rigid heatfluxTG-DSC plate; G, gas entry tube; M, mineral insulated graded heating element; N, liquid nitrogen cooling jacket; R, four bore ceramic hangdown suspended from electronic microbalance; S,fixedcompartment divider with gas ports; T, side branch gas exit pipe; W, water-cooled cold finger.

Figure 1. Schematic diagram of a simultaneous thermal analyser. (Reproduced with Permission from Rheometric Scientific)

In Hyphenated Techniques in Polymer Characterization; Provder, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

In Hyphenated Techniques in Polymer Characterization; Provder, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

TG

ΔΤ ! capillary heater control*

inlet heater control

separator

molecular leak

rotary pump

rotary pump

turbo pump

QUADRUPOLE ANALYSER

τ

printer

recorder or data system

,Τίτττττί

! 8 analogue J outputs

microprocessor control unit + VDU + disc drive

ANALYSER SECTION

analyser hearing control

MASS SPECTROMETER PACKAGE INLET SECTION

Figure 2. Schematic diagram of a STA-MS system (Reproduced with Permission from Rheometric Scientific)

recorder or data system

balance control

DC amp.

MAIN UNIT with balance and furnace

temperature programmer

STA

Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 26, 2015 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1994-0581.ch007

00