Rubber compounding ingredients — Precipitated silica — Determination of aggregate size distribution by disc centrifuge

This document specifies a general method for determining the aggregate size distribution (ASD) of silica by using a disc centrifuge according to the principle of sedimentation. As pre-stage the silica is de-agglomerated in water using strong ultrasonic power treatment. The method is used for precipitated silica.

Ingrédients de mélange du caoutchouc — Silice précipitée — Détermination de la distribution dimensionnelle par à disque centrifuge

General Information

Status
Published
Publication Date
24-Oct-2019
Current Stage
6060 - International Standard published
Start Date
25-Oct-2019
Completion Date
25-Oct-2019
Ref Project

Buy Standard

Standard
ISO 20927:2019 - Rubber compounding ingredients -- Precipitated silica -- Determination of aggregate size distribution by disc centrifuge
English language
14 pages
sale 15% off
Preview
sale 15% off
Preview

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 20927
First edition
2019-10
Rubber compounding ingredients —
Precipitated silica — Determination
of aggregate size distribution by disc
centrifuge
Ingrédients de mélange du caoutchouc — Silice précipitée —
Détermination de la distribution dimensionnelle par à disque
centrifuge
Reference number
ISO 20927:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 20927:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 20927:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Significance and use .......................................................................................................................................................................................... 1

5 Apparatus ..................................................................................................................................................................................................................... 2

6 Reagents and materials ................................................................................................................................................................................. 2

7 Calibration of the test equipment ....................................................................................................................................................... 3

7.1 Calibration of the ultrasonic device ...................................................................................................................................... 3

7.2 Routine alignment check ................................................................................................................................................................ 3

8 Operating instructions ................................................................................................................................................................................... 3

8.1 Preparation of the disc centrifuge .......................................................................................................................................... 3

8.2 Sample preparation ............................................................................................................................................................................ 4

8.3 Cleaning the centrifuge .................................................................................................................................................................... 5

9 Procedure..................................................................................................................................................................................................................... 5

10 Evaluation and documentation of the test results ............................................................................................................. 6

11 Precision data .......................................................................................................................................................................................................... 7

12 Safety precautions .............................................................................................................................................................................................. 8

Annex A (informative) Physical principles of measurement ....................................................................................................... 9

Annex B (informative) Precision data ..............................................................................................................................................................11

Bibliography .............................................................................................................................................................................................................................13

© ISO 2019 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 20927:2019(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www .iso .org/iso/foreword .html.

This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products,

Subcommittee SC 3, Raw materials (including latex) for use in the rubber industry.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 20927:2019(E)
Introduction

The determination of the aggregate size distribution (ASD) of silica by disc centrifuge

photosedimentometry can be used for characterizing and specifying these products. It is well accepted

that the aggregate size distribution of silica could have an influence on the performance of these

materials used in different applications. Therefore, a standardized procedure regarding the sampling

preparation and the testing of the aggregate size distribution seems to be necessary in order to

compare, discuss and interpret received results between the laboratories using this method.

See Annex A for physical principles of measurement.
© ISO 2019 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 20927:2019(E)
Rubber compounding ingredients — Precipitated silica
— Determination of aggregate size distribution by disc
centrifuge
1 Scope

This document specifies a general method for determining the aggregate size distribution (ASD) of

silica by using a disc centrifuge according to the principle of sedimentation. As pre-stage the silica is

de-agglomerated in water using strong ultrasonic power treatment.
The method is used for precipitated silica.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
silica aggregate

discrete, rigid colloidal entity that is the smallest dispersible unit in a suspension

[3]

Note 1 to entry: In comparison to carbon black the term silica aggregate is less defined and has to be seen

always in context with the silica treatment (i.e. ultrasonic power in a silica suspension in water). The references

apply to carbon black but are also broadly used by the rubber industry for precipitated silica.

4 Significance and use

A disc centrifuge is used for measuring the aggregate size distribution (ASD) of precipitated silica.

As a function of test time and rotational speed, aggregate sizes in the range of approximately 5 nm

to 100 µm can be analysed according to the principle of sedimentation. Firstly, the silica sample is

dispersed in an aqueous medium by using ultrasonic power treatment. Afterwards, the suspension is

transferred to the disc centrifuge and separated according to its aggregate size. The sedimentation is

accelerated by centrifugal forces generated by the rotation of the centrifuge. By using a density gradient

of sucrose solution the sedimentation can be stabilised. Over the course of the experiment, a separation

in different silica aggregate sizes is possible and can be evaluated.

For investigations between different laboratories, it is recommended to use the IRM 100 silica

standard according to ASTM D5900 (see Clause 7).

1) IRM 100 silica standard is an example of a suitable product available commercially. This information is given for

the convenience of users of this document and does not constitute an endorsement by ISO of this product. The IRM

100 silica standard can be provided from Balentine Enterprises, INC. (www .irmsilicastandard .com).

© ISO 2019 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 20927:2019(E)
5 Apparatus
The usual laboratory apparatus and, in particular, the following.
5.1 Disc centrifuge allowing a rotational speed of 24 000 r/min.
5.2 Probe-type sonicator typically with a nominal power of 200 W or more.
5.3 Ultrasonic device with a recommended probe size of ½”.

The chosen ultrasonic device shall guarantee that the values of the IRM 100 silica standard in dispersion

are achieved (see Clause 7).
5.4 Cooling bath, e.g. cryostat.
5.5 Precision balance, to ±0,01 g.
5.6 Disposable syringe, 1,0 ml and 2,0 ml with adequate needle size.
5.7 Rolled rim bottles with a recommended size of 35 ml, d = 30 mm, h = 65 mm.

When using the IRM 100 standard, the fixing of the dimension of the vessel is not necessary any longer.

However, an ejection of the suspension should be avoided.
6 Reagents and materials

Use only reagents of recognized analytical grade and only distilled water or water of equivalent purity.

6.1 Water, de-ionized.
6.2 Sucrose, powder, ≥99,7 %.
6.3 Dodecane, 99 %.

6.4 PVC calibration standard with a recommended size of approximately 220 nm ± 20 nm.

The determination of aggregate diameters from the Stokes equation relies on the measurement time

and the knowledge of four other experimental parameters (see Annex B). Since the accuracy of those

parameters strongly depends on other variables, such as the gradient preparation conditions, the

operating temperature in the disc or the stability of rotational velocity, a relevant approach generally

consists in setting the group of four parameters by prior calibration with a standard of known narrow

size distribution. A suitable standard for the characterization of precipitated silica is PVC suspended in

water, but any other standard is acceptable as long as its size distribution (peak and width) and density

is known accurately. A size around 200 nm is a suitable size for rapid calibration.

The PVC standard can be provided by the instrument manufacturer. PVC latex with a narrow particle

size distribution is used. However, slight variations from batch to batch are possible and have to be

considered. The value of a new batch is disclosed by the supplier.
2 © ISO 2019 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 20927:2019(E)
7 Calibration of the test equipment
7.1 Calibration of the ultrasonic device

Independent from the designated power of the ultrasonic generator under 5.2, the geometry of the

ultrasonic probe and the pre-set amplitude, the energy input into the silica suspension can be supposed

on a similar level when the documented parameters of the IRM 100 are in line with the detected results.

Additionally, the probe is underlying some significant ageing effects depending from the number of

tests but also test conditions such as amplitude, time, pulsed/un-pulsed treatment of the suspension.

These ageing effects can influence the ultrasonic power input into the sample and manipulate the

results. The comparison of results with former data or between different laboratories is impeded or

even impossible. By using the IRM 100 as calibration standard, the ageing effects can be detected very

early and precautions up to a replacement of the ultrasonic probe can be undertaken timely.

7.2 Routine alignment check

Before starting a test run, screen the disc centrifuge by using a silica standard. It is recommended to

revert to the international IRM 100 according to ASTM D5900.
Carry out the calibration procedure in accordance with Clauses 8 and 9.

By using the documented test parameters in Clause 9, the following results can be found.

— Mode, linear [nm]: most frequent aggregate size: 66,0 ± 2,8.
— Mean (dw) [nm]: average diameter by weight: 87,8 ± 3,9.
— D (25 oversize weight percentile) [nm]: 97,2 ± 3,3.
— D , median (50 weight percentile) [nm]: 76,4 ± 2,7.
— D (75 oversize weight percentile) [nm]: 60,7 ± 2,5.
— FWHM, linear [nm]: 55,1 ± 2,5.

The given ranges are calculated on a 95 % confidence level based on the total variation determined by

an analysis of variance.

This procedure makes sure that the production of the silica suspension has happened under the same

ultrasonic energy input, independently from the used device and the adjusted conditions (i.e. power of

the generator, ultrasonic time, suspension density, ageing status of the probe, etc). The ageing status of

the probe can be eliminated up to a certain level.

Hereby, it is possible to compare test results received by different laboratories or within one laboratory

(i.e. different operators).
8 Operating instructions
8.1 Preparation of the disc centrifuge

Turn on the disc centrifuge (5.1) and warm up the device as recommended by the supplier. Start

program and set the rotational speed of the disc to 20 000 r/min. When the target speed is reached, fill

the disc centrifuge with a density gradient of sucrose solutions.

The disc speed should be adjusted based on the size range of the sample to be measured. Typical values

are 20 000 r/min to 24 000 r/min for fine silica.
© ISO 2019 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 20927:2019(E)

The solutions of sucrose (6.2) in water consist of different concentrations. These solutions have to be

prepared. The concentrations of sucrose solutions, w , are between 8 % and 24 %. The density

sucrose
gradient is structured in 10 levels:

— 24,0 % - 22,2 % - 20,4 % - 18,7 % - 16,9 % - 15,1 % - 13,3 % - 11,6 % - 9,8 % - 8,0 %

Inject 1,8 ml of sucrose solution per density level into the disc centrifuge, starting with the highest

concentration.

Alternatively, it is possible to prepare only two sucrose solutions with the highest and lowest

concentration: respectively solution A = 24,0 % and solution B = 8,0 %. Mix them together in the

injection syringe (5.6) according to Table 1.

It is also possible to use automatic gradient builder (for example offered by CPS Instruments) for

preparing the solutions of sucrose.
Table 1
1 1,8 ml solution A + 0,0 ml solution B
...

Questions, Comments and Discussion

Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.