1、BRITISH STANDARDBS ISO 18373-2:2008Rigid PVC pipes Differential scanning calorimetry (DSC) method Part 2: Measurement of the enthalpy of fusion of crystallitesICS 23.040.20g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51
2、g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS ISO 18373-2:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 March 2008 BSI 2008ISBN 978 0 580 57185 5National forewordThis British Standard is the UK implementa
3、tion of ISO 18373-2:2008.The UK participation in its preparation was entrusted by Technical Committee PRI/88, Plastics piping systems, to Subcommittee PRI/88/4, Test methods.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not pu
4、rport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.Amendments/corrigenda issued since publicationDate CommentsINTERNATIONALSTANDARDISO18373-2First edition2008-
5、02-15Reference numberISO 18373-2:2008(E)Rigid PVC pipes Differential scanning calorimetry (DSC) method Part 2:Measurement of the enthalpy of fusion of crystallitesTubes rigides en PVC Mthode utilisant la calorimtrie diffrentielle balayage Partie 2: Mesurage de lenthalpie de fusion des cristallitesBS
6、 ISO 18373-2:2008ii iiiContents Page1 Scope 12 Terms and definitions 13 Symbols and abbreviated terms . 24 Principle 25 Apparatus . 26 Preparation of the test pieces 27 Procedure . 38 Expression of results 39 Test report 5Annex A (informative) Possible presentations of DSC curves . 6Annex B (informa
7、tive) Example of peaks due to the presence of additives . 8Annex C (informative) Possible sources of error . 9Annex D (informative) Correlation between enthalpy of fusion and processing temperature 10Bibliography . 11BS ISO 18373-2:2008ivForewordISO (the International Organization for Standardizatio
8、n) is a worldwide federation of national standards bodies(ISO member bodies). The work of preparing International Standards is normally carried out through ISOtechnical committees. Each member body interested in a subject for which a technical committee has beenestablished has the right to be repres
9、ented on that committee. International organizations, governmental andnon-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the InternationalElectrotechnical Commission (IEC) on all matters of electrotechnical standardization.International Standards are dra
10、fted in accordance with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International Standardsadopted by the technical committees are circulated to the member bodies for voting. Publication as anInternational Stand
11、ard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patentrights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 18373-2 was prepared by
12、Technical Committee ISO/TC 138, Plastics pipes, fittings and valves for thetransport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials andtheir accessories Test methods and basic specifications.ISO 18373 consists of the following parts, under the gen
13、eral title Rigid PVC pipes Differential scanningcalorimetry (DSC) method: Part 1: Measurement of the processing temperature Part 2: Measurement of the enthalpy of fusion of crystallitesBS ISO 18373-2:2008vIntroductionStudies have been undertaken at the international level to determine a method of me
14、asuring the enthalpy offusion of crystallites produced during the processing of rigid pipes. These studies have demonstrated that a testusing differential scanning calorimetry (DSC) fulfils these requirements.The method involves taking small samples from the pipe wall and heating these in a differen
15、tial scanningcalorimeter. Small endotherms are used to detect the thermal history of the samples and the enthalpy of fusionof crystallites is derived from these data.The technique requires a good understanding of DSC instruments and techniques, particularly in relation toPVC. It is important that ne
16、wcomers to the technique familiarize themselves with both the instrumentation andmethod prior to undertaking reportable tests.This method is given as a guide and no specific requirement is given in this part of ISO 18373 for the enthalpyof fusion.The method can also be suitable for other types of ex
17、truded rigid PVC products, but different sampling protocolsmight be required.BS ISO 18373-2:2008blank1Rigid PVC pipes Differential scanning calorimetry (DSC) method Part 2:Measurement of the enthalpy of fusion of crystallites1ScopeThis part of ISO 18373 specifies a method for the determination of th
18、e enthalpy of fusion of crystallites in rigidPVC pipe samples. The method is based on the measurement of the thermal history using differential scanningcalorimetry (DSC) and is suitable for all types of rigid PVC pipes.2 Terms and definitionsFor the purposes of this document, the following terms and
19、 definitions apply.2.1 curve magnificationmagnification of the DSC curve around A-onset and B-onset temperature (“zooming”)2.2 A-onsetenthalpy of fusion measurement first indication of “secondary” crystallite melting2.3 B-onsetindication of maximum processing temperature2.4 enthalpy of fusionA-endot
20、hermfusion enthalpy of the secondary crystallites in the pipeNOTE Enthalpy of fusion is expressed in joules per gram.2.5 instrumental baselinemeasurement with empty sample pan, i.e. background subtraction2.6 position of samplelocation in the product from where the sample was taken2.7 purge gasgas us
21、ed to ensure an inert environmentTpHABS ISO 18373-2:200822.8 repeat samplessamples from the same position3 Symbols and abbreviated termsDSC differential scanning calorimetrymaximum temperature reached by the melt during processingenthalpy of fusion4PrincipleDSC is a well-established method for testi
22、ng the enthalpy of fusion, , or A-endotherm, in PVC products(see References 1 and 2). The enthalpy of fusion depends upon processing conditions used to make the pipeand an optimum value reflects a well-processed pipe which will have optimum mechanical properties.The benefits of this test are that an
23、 accurate assessment can be made of the enthalpy of fusion, as well as thepossibility of finding variations in local areas of the product, due to the fact that only a small size of sample isrequired for the test. This enables the operator to cut samples from different locations around the pipecircum
24、ference. Thus, variations in the enthalpy of fusion in the pipe wall may be examined.The characteristic A-endotherm occurs because secondary crystallites produced during the cooling phase afterextrusion of the pipe will melt as the sample is heated, absorbing the latent heat of fusion of these cryst
25、allites asthey do so.5 Apparatus5.1 DSC instrument, and associated software, calibrated.NOTE Calibration should be carried out using at least two different metals. An instrumental baseline must be obtained withan empty sample pan and reference pan in place, and with temperature settings and purge ga
26、s identical to the settings to beused for the sample analysis.5.2 Aluminium sample pans.5.3 Inert purge gas (e.g. nitrogen, argon), of at least industrial quality.5.4 Analytical balance, with an accuracy to within .5.5 Slow speed saw (see Reference 3), knife, or any other device introducing neither
27、heat nor stress intothe sample as it is cut.6 Preparation of the test pieces6.1 Take at least four samples at the , , , and positions, respectively, around the pipecircumference, with all the samples being taken from the centre of the pipe wall.NOTE The samples are taken from the centre of the pipe
28、wall because the processing temperature at the centre of the pipewall is often lower than that close to the inner and outer surfaces, where additional shear occurs.CAUTION Taking samples from the locus of a spider line can lead to an increase in the spread ofresults.6.2 Prepare the test pieces havin
29、g a mass of in a way that maximizes the contact surfacebetween the pan and the test piece.TpHAHA0,01 mg090180270(20 10) mgBS ISO 18373-2:20083NOTE Maximizing the contact surface between the pan and the test piece reduces the resistance to heat flow through theDSC temperature sensors and results in m
30、aximum peak sharpness and resolution.6.3 The best test piece shapes for optimum performance are thin disks placed on the bottom of the pan. Testpieces may be conveniently prepared by cutting out sections with a slow speed diamond saw, or with a razor orknife (5.5). A hole punch or cork borer may be
31、used if the sample is very thin.7 Procedure7.1 Ensure that the scanning device is calibrated.7.2 Encapsulate the test piece in an aluminium pan with cover (5.2).7.3 The test piece shall not move in the pan during the measurement. The most common method of test pieceimmobilization is to crimp the pan
32、 cover in place with a crimper. This yields a tightly, but not hermetically, sealedpan without movement of the test piece in the pan during the measurement. Other methods of pan closure thatimmobilize the test piece can be used.7.4 Using the following test parameters, perform and register the scan:a
33、) start temperature: ;b) end temperature: ;c) heating rate: ;d) purge gas (5.3): .8 Expression of resultsIf necessary, magnify the relevant part of the curve using the zooming feature of the DSC instrument (5.1).Figure 1 depicts a typical curve. The A-onset temperature should lie somewhere between a
34、nd ;if it does not, it is most likely that there is interference in the DSC curve due to the presence of some additive(s)and these must be allowed for. If it is not possible to allow for these interferences, it may not be possible todetermine the enthalpy of fusion for the sample.The enthalpy of fus
35、ion, , is the net area under the curve lying between the A-onset and B-onsettemperatures, after subtracting any area under the curve due to additive peaks. This area is normally calculatedusing the computer software built into the DSC apparatus. A straight line should be drawn between the A-onsetand
36、 B-onset temperatures. Since the value of derives only from the secondary crystallites of the PVC andnot from other components present in the pipe, such as fillers, pigments and stabilizers, the value of should be normalized to account for the PVC content of the pipe. For example, if the PVC content
37、 is bymass, the value of should be divided by 0,99. If it is by mass, then divide by 0,85.NOTE 1 A typical curve consists of two endotherms between approximately and approximately where theA-onset temperature corresponds to the melting of the first “secondary” crystallites and the B-onset correspond
38、s veryclosely to the maximum processing temperature, . The enthalpy of fusion is derived from the first (lower temperature)endotherm. The change in energy levels is usually quite small. See Figure 2 for an example.NOTE 2 Peaks due to additives are generally reproducible.If the standard deviation of
39、the results from three consecutive tests on samples taken from the same location(i.e. the same angular location) within a pipe is greater than , then the furthest outlying result shall bediscarded and another single test carried out. If this does not bring the standard deviation of the results to le
40、ssthan , then the instrument may need recalibrating.Uneven or irregular scan data shall be discarded. See Figure 3 for an example.NOTE 3 The appearance of DSC curves can differ depending upon whether the instrument displays the results via an “exoup” curve (see Figures 1 and 2) or an “exo down” curv
41、e. The latter type produces inverted curves compared with Figures 1and 2. Examples of the different types of presentation are shown in Annex A.(35 15)C225C(20 1)C/min(20 5)ml/min100C 120CHAHAHA99 %HA85 %100C 200CTp1 J/g1 J/gBS ISO 18373-2:20084The presence of some additives can also be detected by D
42、SC and so extra peaks may appear in the DSCcurves as a result. Examples of these are shown in Annex B.Keyheat flow, in milliwattstemperature, in degrees CelsiusA extrapolated peak at : “A-onset”B extrapolated peak at : “B-onset”Figure 1 DSC result curve after zoomingKeyheat flow, in milliwattstemper
43、ature, in degrees CelsiusFigure 2 Typical DSC curve from a PVC pipeT107,9C188,38CTBS ISO 18373-2:200859 Test reportThe test report shall contain at least the following information:a) reference to this part of ISO 18373;b) sample reference number (e.g. production code number of the pipe);c) location
44、from where the samples were taken (e.g. , , , around the circumference of thepipe);d) mean and standard deviation of the enthalpy of fusion expressed as:1) value of as determined from the DSC curve,2) value of normalized for the PVC content of the pipe;e) number of repeat samples tested;f) any facto
45、rs which may have affected the results, such as any incidents, test interruptions or any operatingdetails not specified in this part of ISO 18373 or regarded as unnecessary;g) date(s) of test.Keyheat flow, in milliwattstemperature, in degrees CelsiusFigure 3 Curve that should be discarded because of
46、 severe noise/interferenceT090180270HAHABS ISO 18373-2:20086Annex A(informative)Possible presentations of DSC curvesFigure A.1 shows a typical “exo up” curve and Figure A.2 shows a typical “exo down” curve.Keyheat flow, in milliwattstemperature, in degrees CelsiusFigure A.1 Typical curve from an “ex
47、o up” display with the measured area, , shadedTHABS ISO 18373-2:20087Keyheat flow, in milliwattstemperature, in degrees Celsius1 intersection at Figure A.2 Typical curve from an “exo down” displayT189,4CBS ISO 18373-2:20088Annex B(informative)Example of peaks due to the presence of additivesFigure B
48、.1 shows an example of a spurious peak, due to the presence of an additive, and how it can becompensated for with a best fit secondary line (generated by an experienced technician); is thencalculated as , which should then be normalized for the PVC content, as a percentage bymass, of the pipe.Keyhea
49、t flow, in milliwattstemperature, in degrees CelsiusFigure B.1 Derivation of the area under the curve due to an additiveHA8,0 0,72 = 7,28 J/gTBS ISO 18373-2:20089Annex C(informative)Possible sources of errorPotential sources of error include:a) sample inhomogeneity due to poor mixing of additives and/or poor processing;b) movement of the sample in the pan;c) internal stresses in the material that are released when th
