NZ209160A - Apparatus and method for testing properties of wood pulp sample: wood pulp vibrated against screen - Google Patents

Description

9109160 Sd. Dalt 209160 9 August 1984 NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION "Improvements in or Relating to a Method of Testing Properties of a Wood Pulp Sample and/or Apparatus for Testing Properties of a Wood Pulp Sample" I/We. THE UNIVERSITY OF AUCKLAND, a Body established by the University of Auckland Act 1961, of Princes Street, Auckland, New Zealand hereby declare the invention for which I f we pray that a patent may be granted to me/us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a method of testing properties of fibres in a wood pulp sample and/or a method of predicting the properties of paper sheet and/or apparatus for testing properties of fibres in a wood pulp sample and/or predicting the properties of paper sheet.

The physical properties of a paper sheet depend, to at least a substantial degree, on the type of fibres from which the paper is made and their subsequent refining treatment during the preparation stage.

In New Zealand, pinus radiata forms the current major source of fibre but there are several pulping processes used to convert the wood or wood chips to pulp. Wood density varies with tree age, position in the tree radially and longitudinally, and is affected by other factors such as latitude, elevation, soil type and the like. The mean fibre length and diameter are substantially similar but the cell wall thickness of the fibre varies and hence the fibre density also varies leading to variation in the wood density. This affects the paper sheet bonding and bulk and paper strength properties such as tensile, tear, burst and stretch. Present techniques for differentiating between pulp fibre characteristics, such as the coarseness method, are disadvantageous in that the techniques are laborious, time consuming and difficult to perform.

Similarly where pulp is provided from mixtures of hardwood and softwood, the pulp will Include fibres of differing characteristics such as length and diameter. These characteristics will also affect the physical Properties of paper sheet made from that pulp.

It is therefore an object of the present invention to provide a method of testing properties of fibres in a wood pulp sample and/or a method of predicting properties of a paper sheet and/or apparatus for testing properties of fibres in a wood pulp sample and/or predicting properties of paper sheet which will obviate or minimize the foregoing disadvantages in a simple yet effective manner or which will at least provide the public with a useful choice.

Accordingly in one aspect the invention consists in a method of testing properties of fibres in a wood pulp sample comprising the steps of mixing wood pulp with water, vibrating said wood pulp against a screen or screens and after said vibration determining the t quantity of fibres that have passed through or been retained by said screen or screens.

In a further aspect the invention consists in a method of predicting' the properties of paper sheet comprising the steps of mixing wood pulp with water, vibrating a sample of said wood pulp against a screen or screens and aftefc said vibration determining the quantity of fibres that have "passed through or been retained by said screen or screens, and predicting the selected property or properties of a paper sheet made from said wood pulp from the quantity of fibres that have been passed through or been retained by said screen or screens.

In a still further aspect the invention consists in apparatus for testing properties of fibres in a wood pulp sample and/or predicting properties of paper sheet, said apparatus comprising two or more chambers, a screen or screens between said chambers, means to vibrate material in at least one said chamber against said screen or screens, an inlet to said chambers and closable outlets from each said chamber.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense t limiting.

One preferred form of the Invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of part of apparatus for testing the ratio of thin wall to thick wall fibres in a wood pulp sample and/or predicting properties of paper sheet according to one preferred form of the invention; screen usable In the apparatus of figure 1; Figure 3 is an end elevation of the apparatus of figure 1 mounted on a suitable track; Figure 4 is a side elevation of the apparatus of figure 3; Figure 5 is a graph of results obtained from the apparatus of a preferred form of the invention and the fibre coarseness of various pulp samples; Figures 6 to 9 and 11 are graphs showing the percentage mass fraction in the first chamber of the apparatus of a preferred form of the invention plotted against respectively handsheet bulk, tear index, burst index, breaking length and stretch after beating of the pulp; and Figure 10 is a graph of results obtained from the apparatus of a preferred form of the invention being % mass retained in the first chamber against % mass of hardwood or softwood. t In the preferred form of the invention a method of testing properties of fibres in a wood pulp sample and/or a method of predicting properties in paper sheet and/or apparatus for testing properties of fibres in a wood pulp sample and/or predicting properties in paper sheet are provided as follows: The apparatus of the invention comprises two or more chambers such as a pair of chambers 1 and 2 which are separated in the preferred form by a screen 3. If more than two chambers are required such as three chambers then further screens such as two screens are provided. The screen 3 may be removably positioned in a groove or slot 4 between the chambers 1 and 2 which may therefore be formed as a single item. The chambers 1 and 2 may be formed by providing the construction in the form of a base part 5 and a lid part 6, for example, connected through a hinge 7 therebetween. The base part 5 and lid part 6 are able to be closed one to the other, for example, by providing a flange 8 on the base part 5 and a flange 9 on the lid part 6. The flange 8 may have one or more and for example two apertures 10 therein and corresponding slots or apertures 11 may be provided on the flange 9 so that a connecting device such as, for example, bolt 12 and nut 13 may be passed therethrough to secure the construction.

The construction is completed by end walls 14 and 15 over which the lid may engage.

An inlet is provided which may comprise an aperture through the lid part 6 or other parts of the construction such as the end walls.

The mesh size of the mesh or screen 3 is any suitable size and it has been found that for pinus radiata thin wall/thick wall fibre determinations 16 mesh is suitable for use in the invention. For hardwood/softwood determinations other mesh sizes may be required.

In order to perform the method of testing of the invention the chambers 1 and 2 must be reciprocated or vibrated and this may be achieved by providing wheels, rollers, slides or the like, for example, wheels 20 on axles 21 which wheels 20 run in tracks 22 mounted on a suitable stand 23 which has a slot 24 on the upper face thereof so that outlets 25 from the chambers 1 and 2 may pass through the slot 24 in use.

In order to effect the reciprocal motion, a crank 30 is provided, for example, in the form of a wheel driven by motor 31 and pivotally connected between the crank 30 and the chambers 1 and 2 is provided a connecting arm 32. The positioning of arm 32 is adjustable to vary the "throw" of the reciprocal movement if desired. Alternatively any other electronic, electric, pneumatic or hydraulic actuator may be used or employed.

In use the stop cocks 25 are closed. The pulp fibre mix is then prepared to a prespecified concentration and entered into one chamber e.g. chamber 1* The lid is then closed and the construction vibrated for a predetermined period of time. Once stopped the liquids are drained from the chambers 1 and 2 and the samples are filtered for example by use of filter paper. Once filtered the samples are dried in an oven and weighed. The properties of the pulp are then calculated. So as to obtain an effective draining of the chambers 1 and 2 the throat diameter of stop cock valves 25 should be relatively large. In use in a thinwall/thickwall determination the more flexible or thin walled fibres will tend to pass through the screen into chamber 2 more readily leaving the less flexible or thick walled fibres in chamber 1. The apparatus therefore provides substantial separation of the thick and thin walled fibres. With fibres from mixed hardwood softwood samples the longer wider fibres will be less likely to pass through the mesh again leading to a separation.

The precise construction of the chambers 1 and 2 and operating requirements need not be rigidly defined but it has been found that the optimum oscillating amplitude is about 30mm and a screening time of about 2 minutes has been found satisfactory. An oscillating frequency of about 360 rpm has also been found satisfactory but will depend on chamber size. It has been found that an operating amplitude of 20mm gives insufficient separation whereas 40mm amplitude creates greater noise and wear whilst showing no substantial improvement in fibre separation.

Similarly a 1 minute screening time is found to give less separation than 2 minute screening whereas longer times do not markedly increase the separation of the thick wall and thin wall bulk fibres. Hardwood/softwood separation will usually require longer screening times such as, for example, 5 minutes.

It has been found that a stock consistency of 0.140% J/r ' O is close to the optimum with an acceptable tolerance of ± 0.005*.

It has been found that reproducability of the results of a skilled operator can be within ±1%.

Referring to the graphs figure 5 is a plot of apparatus results and the fibre coarseness of various pulp samples. The entries marked "S" are slabwood and the entries marked "C" are corewood. This graph shows that the apparatus is capable of differentiating between the different pulps. The scatter of the results is mainly due to the limited accuracy of the coarseness determination within the acceptable uncertainty of ± 1mg per 100m. So as to evaluate the capability of the apparatus more accurately, correlations were then sought from conventional pulp handsheet properties. The square of the regression co-efficient for the readings forming figure 5 is 0.65.

Graphs 6 to 9 and 11 show percentage mass fraction in chamber 1 against handsheet properties with handsheets r made from beaten pulp. A lampen mill beating of 1000 revolutions was chosen as this was thought to be sufficient to bring out the characteristics of the fibres, result in good handsheet formation and is in accordance with standard sheet evaluations. The slabwood pulp would respond less to the beating because of the higher proportion of the thick wall fibres.

It can be seen that results achieved from this ,10JULl987 r*cr testing show for percentage mass fraction in chamber 1 against handsheet bulk a regression co-efficient squared of 0.9i for percentage mass fraction in chamber 1 against tear index a regression co-efficient squared of 0.87, for percentage mass fraction in chamber 1 against burst index a regression co-efficient squared of 0.74, for percentage mass fraction in chamber 1 against breaking length a regression co-efficient squared of 0.64, and for percentage mass fraction in chamber 1 against stretch a regression co-efficient squared of 0.82. These results suggest that the percentage mass fraction in chamber 1 is a reliable guide to the properties of handsheet bulk, tear index, burst index, breaking length and stretch that can be expected in paper, samples of the wood pulp used in the making of which have been tested by the apparatus and method of the invention. Thus for a given screen mesh size various paper sheet properties can be determined for a given percentage mass fraction retained in chamber 1. Thus charts can be developed such as empirically to predict paper sheet properties for a given percentage mass fraction retained in chamber 1.

When the same handsheet properties are graphed using fibre coarseness testing methods, corresponding regression squared co-efficients of 0.72, 0.73» 0.47, 0.48 and 0.56 have been found thereby indicating that the method of the present invention provides a more U-1 m satisfactory assessment of the paper properties than the ' fibre coarseness method.

Figure 10 shows a group of % mass retention in chamber 1 plotted against the mass % hardwood or mass % softwood.

Again the results show a substantial degree of reproducability. The screen used for these tests was 20 xnesh with 1 mm square holes, and 20 wire threads per inch. For summerwood/springwood determinations a 14 mesh screen with 1.36 mm square holes is useful.

It has also been found that there is no substantial significant effect of P number on the apparatus results. P number is the number of mis (millilitres) of O.IK (normal) permanganate solution which is absorbed by lg (gram) of OD (oven-dry) pulp fibre. The percentage mass fraction and P > number have shown no direct relationship and percentage mass fraction in chamber 1 against P number have been found in tests to have a regression co-efficient squared of 0.097.

Thus it can be seen that a method of testing the 0 properties of fibre in a wood pulp sample and/or a method of predicting properties of paper sheet and/or apparatus j for testing properties of fibres in a wood pulp sample and/or predicting properties of paper sheet is provided which at least in the preferred form of the invention has 5 the advantage that a substantial determination of the properties of paper made from that wood pulp may be achieved in a simple yet effective manner. *oyiou differentiating between pinus radiata at least corewood and slabwood pulp more accurately than the coarseness method presently used. Also hardwood/softwood ratios can be determined.

Correlation of the apparatus results with conventional pulp handsheet properties are excellent when compared with fibre coarseness and pulp property correlations. The operation of the apparatus is simple with good reproductive results and the results of the analysis can be obtained within minutes, usually less than 20 minutes. The separation of the fibre types has also been found not to be affected by P number in the range of 16 to 31. 3

Claims (2)

1. WHAT WE CLAIM IS: 1. A method of testing properties of fibres in a wood pulp sample comprising the steps of mixing wood pulp with water, vibrating said wood pulp against a screen or screens and after said vibration determining the quantity of fibres that have passed through or been retained by said screen or screens.
2. 2. A method of testing properties of fibres in a wood pulp sample as claimed in Claim 1 wherein said step of vibrating said wood pulp against said screen comprises the steps of providing a pair of chambers separated by said screen, placing said wood pulp in a first of said chambers and vibrating said chambers and said screen. 3* A method of testing properties of fibres in a wood pulp sample as claimed in either Claim 1 or Claim 2 wherein said step of determining the quantity of fibres that have passed through said screen comprises measuring the ratio of the mass of material remaining in said first chamber against the mass of material Initially placed in said first chamber.;4. A method of testing properties of fibres in a wood pulp sample as claimed in any one of the preceding Claims wherein said wood pulp sample comprises a mixture of thick wall and thin wall fibres.;5. A method of testing properties of fibres in a wood pulp sample as claimed in any one of Claims 1 to 3 wherein said wood pulp sample comprises a mixture of fibres having differing lengths and diameters.;6. A method of testing properties of fibres in a wood pulp sample substantially as herein desribed with reference to the accompanying drawings.;7* A method of predicting the properties of paper sheet comprising the steps of mixing wood pulp with water, vibrating a sample of said wood pulp against a screen or screens, after said vibration determining the quantity of fibres that have passed through or been retained by said screen or screens, and predicting the selected property or properties of a paper sheet made from said wood pulp from the quantity of fibres that have passed through or been retained by said screen or screens. 8. A method of predicting the properties of paper sheet as claimed in Claim 7 wherein said step of vibrating said wood pulp against said screen comprises the steps of providing a pair of chambers separated by said screen, placing said wood pulp in a first of said chambers and vibrating said chambers and said screen. 9. A method of predicting the properties of paper sheet ' t as claimed in either Claim 7 or Claim 8 wherein said step of determining the quantity of fibres that have passed through said screen comprises measuring the ratio of the mass of'material remaining in said first chamber against the mass of material initially placed in said first chamber. 10. A method of predicting the properties of paper sheet as claimed in any one of Claims 7 to 9 wherein said wood pulp sample comprises a mixture of thick wall and thin wax fibres. 11. A method of predicting the properties of paper sheet as claimed in any one of Claims 7 to 9 wherein said wood pulp sample comprises a mixture of fibres having differing lengths and diameters. 12. A method of predicting the properties of paper sheet substantially as herein described with reference to the accompanying drawings. 13. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulpr said apparatus comprising two or more chambers, a screen or screens between said chambers, means to vibrate material in at least one said chamber against said screen or screens, in a direction substantially normal to the plane of said screen or screens, an inlet to said chambers and closable outlets from each said chamber. 14. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting the properties of paper sheet made from said vood pulp as claimed in Claim 13 wherein said chambers have an openable lid. 15. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulp as claimed in either Claim 13 or Claim 14 wherein an outlet from each chamber is provided having a substantially large aperture size. 309 /v <10 JUL 1$ 16. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulp as claimed in any one of Claims 13 to 15 wherein said chambers are mounted on rollers, wheels or the like able to move on a track and a means is provided to effect reciprocal movement of said chambers. 17. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulp as claimed in Claim 16 wherein said means to effect reciprocal movement of said chambers comprises a crank and an arm pivotally connected between said crank and said chambers. 18. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulp as claimed in any one of Claims 13 to 17 wherein said screen has a mesh size between 14 and 2Q. mesh. 19. Apparatus for testing properties of fibres in a sample of wood pulp and/or predicting properties of paper sheet made from said wood pulp substantially as herein described with reference to the accompanying drawings. r\. si. rnm\ « OVJ1N PER AGENTS FOR THE APPLICANT V