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T 7 - Taschner - Triacetine in cigarette filter - "Do we get what we add?"
Triacetine in cigarette filter - "Do we get what we add?"
Petra TASCHNERH.F. & Ph.F. Reemtsma GmbH, Research & Development, Albert-Einstein-Ring 7, 22761Hamburg, Germany.
Triacetin is the most commonly used plastiziser for cellulose acetate filters. To get asufficient hardness, target values for triacetin vary typically between approximately 6 and 9 %of the total filter weight. In the course of applying triacetin to a given cellulose acetatequality, there are some well-known factors that must be considered to achieve the mostconsistent application: - tow band width - type of application device (geometric shape, brushes and jets) - machine line speed - percentage of plasticizer applied
Additionally, some properties of the basic material itself combined with the ambient climatein the manufacturing site (mainly relative air humidity) play an important role in the filter rod,such as the moisture regain.
Investigating the triacetin content in filter rods during the manufacturing process are drivenby several reasons. The main objective in the light of production control is to avoid soft rodsand poor distribution of triacetin. Besides, it is also known that triacetin transfers into themain smoke, contributing to tar.
For production control purposes, the application of triacetin is normally monitored andadjusted by the weight difference between "dry" and "wet" filter rods, carried out on a regularbasis throughout production. If details regarding the triacetin distribution on a filter rod ortip-to-tip variation are needed, more sensitive and time-consuming methods have to be used.
Mainly GC techniques, but also spectrophotometric methods as well as NMR techniques, areused for this purposes. Currently, there is no harmonised or generally accepted or recognisedmethod available.
In 1999 Rhodia, Hauni, Filtrona and Reemtsma in Germany agreed to start activities ontriacetin, addressing in a first step the issue of methods to quantify triacetin. Four GCmethods were in use in the companies (table 1a, 1b), each of them was adjusted to thespecific purpose of analysis, such as analysing tow material, freshly produced filter rods orfilter tips of finished products.
inj. / det. temp.
The group conducted in 1999 a trial where each laboratory used its own in-house GC method.
For this purpose tow material treated with 5 different triacetin levels (3 to 15%) was speciallyprepared by courtesy of Rhodia. After spiking, the tow portions were shredded to achievehomogenous material for the trial. Table 2 summarises how the trial was carried out.
triacetin levels (%)*
no. of replicates (extraction)
no. of replicates (injection)
reporting of data
no. of data (mean of 2 inj.)
As this trial was based on 4 laboratories only and was designed to be a first cross-check, basicstatistical values were calculated without any outlier deletion.
From the single results in figure 1 it can be seen, that: - Lab A's results are below the target values for each level - Lab B and C show smaller standard deviation, compared to Lab C - Lab B, C and D are in good compliance for the lower levels, whereas for the higherlevels there is a constant ranking (Lab B < Lab C < Lab D)
The 4 methods used for this trial differ mainly in the extraction procedure, such as theextraction solvent, sample/solvent ratio and the also the extraction techniques: regarding theextraction solvent, a higher sufficiency was observed by using either pure alcoholic solvents(Labs B, C, D) than a mixture with acetone (Lab A). Comparing the extraction technique,there seems to be also a benefit from the Soxhlet extraction (Lab C) compared to the otherextraction techniques, as fresh solvent is continuously delivered during the extraction.
Another issue raised, when the group discussed the cross-check results, as the moisturecontent of the tow material was not considered in the protocol. Moisture has not only animpact on the extraction conditions by modifying the solvent polarity, but also triacetin itselfinfluences the moisture of the tow material. To address this point for the analytical work, itwas suggested that samples should be conditioned - preferably under ISO climate - prior toanalysis and to perform additional tests investigating the moisture regain.
In summary, none of the 4 original GC methods was identified to meet the requirements for amethod applicable to tow material, filter rods and filter tips. Further work will be carried out
by the group in this field, taking into account the results mentioned above.
Nevertheless, one company, Rhodia; investigated the tip-to-tip variance by using theirin-house method. Ten filter rods produced under identical conditions on KDF 2 and KDF 3from tow material 3,0Y35000 were directly taken from the rodmaker, cut into segments of 21mm and each segment was analysed separately via GC. The results for the individualsegments show a remarkable variation in the distribution of triacetin. Figure 2 representsresults for 5 out of 10 rods for both rodmaker:
For both types of rodmaker the triacetin mean values over 10 rods ranges between 7 and 9%,where within one single rod even higher variation can be observed.
For production control purposes, the application of triacetin is normally monitored andadjusted by the weight difference between "dry" and "wet" filter rods, expressed as "%triacetin". Different possibilities to calculate the results or to define target values are in use,including or excluding the weight of plug wrap, glue or even the tow.
For using the weighing procedure, a defined number of filter rods are ejected from therodmaker without stopping the triacetin application, and a respective number of rods areejected after stopping the application. The latter still contain triacetin depending on various
factors, such as: - the volume of ejected rods - brush rotation - machine line speed (g tow per minute) - type of rodmaker and application device
In one production facility the triacetin content of "dry" and "wet" rods was investigated viaone the GC methods and the routine wet/dry method during the normal production over a 1week period. 6 machines were included, equipped with 2 different types of rodmaker adjustedto different line speeds. For each machine at least two times per production shift samplingwas carried out on at least 2 days. Sampling of dry rods was performed following thecommonly used procedure: 3 seconds after stopping the application and brush rotation, 25 dryrods are ejected to form the "dry" sample. The corresponding "wet" sample is collected justbefore stopping the application. All samples were stored in properly sealed flasks prior to GCanalysis. Table 3 contains relevant details about the samples.
line speed (m/min)
Based on the line speed adjusted at the machine and the rod length, the number of rodsdiscarded prior to ejecting the "dry" sample differs between 110 and 300. Table 4 lists thenumber of rods discarded and the corresponding triacetin range determined in the "dry"sample for each machine:
n° of rods
For both types of rodmaker triacetin residue were detected in the "dry" rod samples, withmore constant and lower residue values for the KDF 3, where higher numbers of rods (300)are discarded before ejecting the "dry" sample.
The triacetin content in the so-called dry rods is well-known and should be taken into
consideration by inserting a factor into the wet/dry-calculation, which is ideally definedindividually for each machine/filter-combination. Otherwise, the wet/dry results wouldpretend too low triacetin contents: example from table 4: machine 2 (slim filters) target value 8 % triacetin result wet 428 mg result dry 398 mg
Without any correction the wet/dry result would be 7,54 %.
Corrected by 0,9 % (or 3,6 mg) - representing the triacetin still included the dry weight - theresult is 8,63 %. Under routine production conditions one overall factor is normally used tocorrect the wet/dry values.
Finally, on 1 machine a modified sampling was carried out, where the brush rotation wasstopped at different times (with a delay of 0 to 4 sec. after stopping the triacetin application).
The influence of the brush rotation could be seen from figure 3. Even when the brush rotationhas been stopped simultaneously with the triacetin application, significant contents are foundon dry filter rods:
Stop-Time brush rotation vs. triacetin (dry rods)
Depending on the line speed, even a short delay contributes to additional triacetin on theejected dry rods. Therefore it is recommended to stop brush rotation simultaneously with theapplication.
Several GC methods are in use for the determination of triacetin. For none of these methodsthe suitability for both sample types - filter rods and filter tips - has yet been proofed. Furthermethod development is therefore necessary.
For production control purposes several aspects regarding the wet/dry method have to beconsidered to avoid misinterpretation of results. An unique protocol about sampling shouldbe available and strictly followed, including the determination of triacetin content in dry rodsfor each individual machine, as well as to consider adequately the moisture contents.
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