Processing promoters - keys to successful compounding.

The goal of this article is to provide a better understanding and appreciation of processing promoters. It is hoped that by explaining how processing promoters function and showing a few examples, you will feel more comfortable in selecting and using them.

In the broadest definition, a processing promoter is a chemical that facilitates or, indeed, makes possible the production and processing of rubber compounds.

Specifically, a good processing promoter should be able to improve mixing and processing characteristics of a rubber stock, and preferably improve physical properties of the vulcanizate, without changing cure behavior.

Over the long history of the rubber industry, as mixing or processing problems presented themselves, solutions were found empirically, i.e., a `try this, try that' approach. Through this trial and error process and good observations, certain chemicals were found that produced the desired changes. It was found that the different problems could be grouped into categories and the chemicals that solved these problems could likewise be grouped into families. Table 1 summarizes the families of chemicals that produce certain effects. This article will focus on mastication aids, dispersants, lubricants and homogenizers.

Table 1 - processing promoters according to
their effect

Effect                  Examples

Mastication aids        Pentachlorothiophenol and its
                        Zinc salts
                        Diaryldisulfides

Dispersants             Fatty acids
(internal lubricants)   Metal soaps
                        Fatty acid esters
                        Fatty alcohols

Lubricants              Metal soaps
(external lubricants)   Fatty acid esters
                        Fatty acid amides
                        Low mw hydrocarbons

Homogenizers            Hydrocarbon resins
                        Fatty acid derivatives
                        Bitumen

Tackifiers              Phenolic resins
                        Coumarone-indene resins
                        Hydrocarbon resins

Reinforcing agents      Phenolic resins

Assembling agents       Factice (vulcanized vegetable oil)

Table 1 shows that the same chemicals are listed for both dispersants and lubricants, with the term internal lubricants in parentheses under dispersants, and the term "external lubricants" in parentheses under lubricants. These differences will be explained when we study the theory of processing promoters and amply demonstrated with examples.

Theories

Lubricity theory

The first is called the lubricity theory in which a polymer matrix is likened to a pile of nonwoven fibers, somewhat like a piece of felt. The individual fibers are the polymer chains. Because they are randomly oriented and entwined, they are difficult to move. If a plasticizer/lubricant is introduced between the chains, then they become physically separated and can slide past one another more easily; consequently, the whole mass is more deformable.

Gel theory

In the gel theory, the stiffness of the polymer chain is due to a three-dimensional structure or gel-like network with active sites along the chains serving as hooks between the chains. By adding a plasticizer/lubricant, these points of attraction are masked and there is a swelling of the gel so deforming is made easier.

Free-volume theory

The free-volume theory proposes that the presence of a plasticizer lowers the glass transition temperature of the polymer. In so doing, it increases the free volume of the matrix, which is a function of temperature and structure.

In practice, the percentage of any one theory to a given application depends to a large extent on the particular polymer being used. The first theory best describes the case for very nonpolar hydrocarbon polymers like EPM and EPDM. The second theory would apply to polar polymers like NBR and EVM, as well as highly unsaturated polymers such as NR, SBR, IR, etc. The third theory would apply more to the thermoplastic polymers.

The assumption made in all of the theories is that the plasticizer/lubricant ends up between the polymer chains. In layman's terms, this refers to solubility. Solubility or insolubility of the processing promoter in the polymer determines its function on the mixing and processing characteristics of the compound.

This relationship between solubility and performance can be described as follows: Polymer soluble processing promoters are known as internal lubricants. They swell and lubricate the polymer chains, thus facilitating dispersion of ingredients.

Polymer insoluble processing promoters are known as external lubricants. They tend to migrate to the surface of the compound, thus facilitating release from metal surfaces such as mill rolls or mixer rotors, and improve extrusion and injection molding characteristics where rubber is sliding over metal surfaces.

A processing promoter consisting of a blend of ingredients (Aflux 42M) will be used to show that a given product can perform different functions in different polymers. The function of a processing promoter in any given polymer is determined by its solubility in that polymer, as shown in table 2.

Table 2

              EPDM   NR   CR   NBR

Alcohols       0     1    7    7
Fatty acids    2     3    5    8
Esters(*)      2     3    5    10
Total          4     7    17   25

The ratings are from 0 to 10 where 0 means total
insolubility and 10 means total solubility

(*) Esters of fatty alcohols and fatty acids

(**) Pentaerythrityltetrastearate

After summing the relative solubilities of the various components of the processing promoter in the various polymers, it is obvious that it is not very soluble in EPDM, a little more soluble in NR, more soluble in CR and very soluble in NBR. So, theoretically, the processing promoter will behave as a lubricant in EPDM and even NR, whereas it will perform as a dispersant in CR and NBR. Keep in mind that in reality, since most processing promoters are blends, they can do some percentage of both functions simultaneously, the percentage depending on the particular polymer.

Mastication

Mastication is the process, especially dramatic in the case of natural rubber, in which the higher molecular weight polymer chains are broken into smaller units to reduce the "nerve" of the rubber, lower the viscosity, and improve flow properties. This process can be carried out using either mechanical shear or a combination of mechanical shear and chemical peptizers.

Mechanical mastication

Mechanical mastication yields a homogeneous and smooth rubber compound with good flow properties that produces a vulcanizate with good physical properties. However, mechanical mastication takes a long time and requires a lot of energy.

Chemical mastication using peptizers

Some commercially available chemical peptizers include (a) activated pentachlorothiophenol; (b) the zinc salt of pentachlorothiophenol; (c) di-o-benzamidophenyl disulfide; (d) zinc 2-benzamidothiophenate; (e) activated mixtures of fatty acids, soaps of fatty acids and fatty alcohols; and (f) others.

The use of chemical peptizers shortens the required mixing time and generally reduces the total amount of required energy. However, there are several disadvantages associated with the use of chemical peptizers, such as:

* Distribution problems with small amounts of peptizer;

* masterbatch is not homogeneous;

* masterbatch stickier and not easy to process;

* SBR and NR/SBR blends tend to form gel.

Since these are very powerful chemicals, they are consequently used in small quantities. Because they are used in small quantities and are mixed in short mixing cycles, one frequently experiences distribution and dispersion problems. For example, the masterbatch might not be homogeneous due to undispersed particles of peptizing agent. This leads to "hot spots." The polymer chains immediately surrounding these pockets of chemical peptizer are broken into smaller segments than in the bulk of the mix. These little domains of low MW polymer are tacky. In fact, natural rubber stocks peptized with small concentrations of chemical peptizers are generally more sticky and tacky due to the formation of more low MW fragments.

Second, in NR/SBR blends, some of the SBR crosslinks and forms gel. This phenomenon is referred to as cyclization.

To minimize the problems mentioned above, some suppliers of processing promoters used for peptizing natural rubber and NR/SBR blends have developed diluted forms of these active chemical peptizers. The chemical peptizer is generally dissolved or diluted in a zinc soap, which, as you will see later, is itself a processing promoter.

The main advantages of using diluted chemical peptizers are:

* Efficient peptization, even at mill temperatures as low as 60 [degrees] C;

* reduce mixing time;

* facilitate more homogeneous distribution of the active chemical resulting in no hot spots, less surface tackiness and less mold fouling in injection molding;

* improve overall flow characteristics of uncured stocks;

* facilitate more homogeneous dispersion of fillers/curatives;

* eliminate tendency toward cyclization in SBR and NR/SBR blends;

* polymer retains higher overall average molecular weight resulting in better carbon black dispersion due to higher shear and overall improvement in physical properties.

Table 3 shows the inconsistency of a stock mixed with a chemical peptizer based on activated pentachlorophenol and the homogeneity of a stock mixed with a diluted chemical peptizer based on an activated zinc soap. After equal mix times of 60 seconds, the viscosity of the stock mixed with the "diluted peptizer" is significantly lower than that mixed with the "pure peptizer." This holds true even as the speed of the internal mixer is increased from 60 rpm to 80 rpm. However, of particular interest, is the variation in viscosity within each batch. The variation in the stock mixed for 60 seconds at 60 rpm with pure peptizer shows a variation of almost 10 Mooney points, whereas the stock mixed under the same set of conditions with the diluted peptizer shows a total variation under four Mooney points. Although the differences become less with more shear, the stock containing the diluted peptizer still shows about half the variation as the stock with the pure peptizer.

Table 3 - peptizing effect of "diluted" versus
"pure" peptizers

The conditions were as follows:

  BR laboratory internal mixer
  40% fill factor
  60 second mix time
  Rotor speed: 60 rpm

Ingredients:

  SIR 20 natural rubber
  0.3 phr "pure" peptizer
  2.0 phr "diluted" peptizer

Test procedure:

  Each batch passed once through a 1/4" open mill
  Each batch cut into 16 pieces
  Mooney viscosity at 100 [degrees] C determined on all pieces
    from center and edges of "sheeted" batch

    Test results (Mooney viscosity at 100 [degrees] C)

Mixed 60 sec. at 60 RPM:   Mixed 60 sec. at 80 RPM:

"Pure"   "Diluted"          "Pure"   "Diluted"
 61.3      54.2              63.4      53.4
 68.3      55.5              63.6      54.1
 70.9      58.0              67.0      55.8

Another significant difference is the time to achieve dispersion of the carbon black. Table 4 shows the incorporation rate of carbon black into stocks mixed without processing promoter (only stearic acid), Renacit 7, Aktiplast F and Aktiplast M. As you can see, it took 63 seconds for the carbon black to be incorporated into the stock without processing promoter, 45 seconds for carbon black incorporation into the stock with Renacit 7, 45 seconds for carbon black incorporation into the stock with Aktiplast F, and only 24 seconds for carbon black incorporation into the stock with Aktiplast M.

Table 4 - carbon black incorporation as a
function of peptizing agent

Recipe                 A      B      C      D

SIR 10               96.0
SBR 1516              4.0
Carbon black N-330   60.0
Naphtolen ZD          8.0
Vulkanox 4010         1.2
Vulkanox 4020         0.8
Vulkanox HS           1.0
Antilux 654           1.2
ZnO special           3.0
Vulkacit DOTG         0.2
Vulkacit TMTD         0.2
Vulkacit TBBS         1.0
Sulfur                2.0
Rhenogran CTP-80      0.3

Stearic acid          2.0    1.0    1.0    1.0
Renacit 7              --    0.2     --     --
Aktiplast F            --     --    2.0     --
Aktiplast M            --     --     --    2.0

Carbon black
  incorporation      63.0   45.0   45.0   24.0
  (seconds)

In this study, the polymers were masticated 60 seconds, the ram raised, the carbon black added, the ram closed and the mixing started. As the carbon black was being incorporated into the stock, the viscosity of the stock increased and the power consumption increased. After the carbon black was incorporated into the rubber, the viscosity began to drop and the power consumption began to drop. The time between when the ram was lowered and the time the power consumption curve began to go down was taken as the carbon black incorporation time. The carbon black incorporation times were determined from the power consumption charts shown in figure 1.

[ILLUSTRATION OMITTED]

Since we have just shown that actuated zinc soaps provide faster incorporation time, we will demonstrate the improved properties obtained by this improved carbon black dispersion. To do this, two identical stocks were mixed, one with and one without the activated zinc soap, for each type of carbon black from low surface area to high surface area. The recipe and mix procedure are shown in table 5. The results of the study are shown in table 6.

Table 5 - improving dispersion of high surface
area carbon black using zinc soaps

Recipe:

SMR-20           70
Polybutadiene    30
Carbon black     65
Zinc oxide        3.5
Stearic acid      1.6
6-PPD             1.5
TMQ               1.5
MBS               0.9
Sulfur            1.5
                110.4

Mixing procedure:
  First cycle: 80 rpm, water on one-half
  Load rubber and Aktiplast M (if present) ram down
      0' Start time
     50" Raise ram, add all ingredients except Santocure
         MOR and sulfur
      2' Raise ram, sweep, ram down
  3-1/2" Raise ram, discharge, pass through open mill
  Second cycle: 80 rpm, water off
  Load all ingredients, ram down
      0' Start time
     50" Raise ram, scrape, ram down
  1-1/2" Raise ram, discharge, pass through mill
Table 6 - zinc soaps excel in dispersing high
surface area carbon blacks

                             A      A'      B       B'      C       C'

Compound                   10.4   110.4   110.4   110.4   110.4   110.4
Aktiplast M                   2      --       2      --       2      --
N-330                        65      65      --      --      --      --
N-220                        --      --      65      65      --      --
N-110                        --      --      --      --      65      65
Naphthenic oil               15      16      15      16      15      16

ML 1+4(100 [degrees] C)      89    >200    >200    >200    >200    >200

Cure @ 330 [degrees] F
[T.sub.2]                   1.8     1.7     1.8     1.7     1.8     1.9
[T.sub.90]                  4.4     4.0     4.7     4.2     4.3     4.3
Minimum                    19.3    24.0    23.6    26.7    29.4    32.5
Maximum                    79.7    79.0    79.2    75.2    78.4    75.8

Cure 10' @ 330
  [degrees] F

Modulus, psi
100%                        590     610     750     750     630     720
200%                      1,480   1,480   1,750   1,680   1,530   1,500
300%                      2,410   2,350   2,760   2,620   2,530   2,410
Tensile psi               3,410   3,270   3,450   3,220   3,650   2,940
Elongation, %               430     420     370     370     430     360
Shore A                      71      71      72      71      74      74
Die C [tear.sup.1]          471     450     434     440     432     402
Rebound, %                   47      45      42      42      42      42
[sup.1] lbs. f/in.

It is quite obvious in every case that the tensile strength values for the stocks containing the activated zinc soap are significantly higher than those for the controls. It is especially noticeable in the case of the N110 carbon black where the processing promoter allowed for the complete and homogeneous distribution of the carbon black, thus facilitating the exceptional properties expected of such a carbon black.

One practical use of an activated zinc soap is demonstrated in a typical NR/BR retread stock, shown in table 7. In this very complicated, highly loaded retread stock containing both NR and BR, two different kinds of filler, and a relatively low level of oil, the use of an activated zinc soap makes it possible to mix this compound in 8.5 minutes using only two passes as opposed to a conventional three pass mix taking 12 minutes.

Table 7 - activated zinc soap in a retread stock

Recipes                           A              B
                             (3 pass mix)   (2 pass mix)

SMR 20                             60             60
BR                                 40             40
Rhenosin 145A                     1.5            1.5
Aktiplast M                        --              2
Tread black                      45.6           45.6
HiSil                            18.1           18.1
Stearic acid                        2              2
Zinc oxide                          4              4
6-PPD                             1.5            1.5
TMQ                               1.0            1.0
Antilux 654                       0.7            0.7
Oil                                15             15
TBBS                              0.9            0.9
PVI                               0.2            0.2
Sulfur                            1.5            1.5
Total mix time (min.)            12.0            8.5
ML(1+4) 100 [degrees] C            70             69
Extrusion speed (cm/min.):        102            111
Extrusion output (g/min.):         97            105
300% modulus (MPa):              11.0           11.7

Comparing the physicals of the two stocks, it is obvious that they are very similar. The only apparent difference between the two stocks is that the one mixed with the activated zinc soap has a lower tan delta, which suggests lower heat buildup and thus better tire life.

There are two rules of thumb when using chemical peptizers. First, the chemical peptizer is added to the polymer at the very beginning of the mix cycle. Second, mix as long as possible before introducing the antioxidant.

Dispersants and lubricants

As you saw earlier, the same families of chemicals that are used as dispersants are also used as lubricants. It is the goal here to show that the basic reason a processing promoter will either function predominantly as a dispersant (internal lubricant) or a lubricant (external lubricant) - (in reality they do some percentage of both simultaneously) - is the solubility of the processing promoter in the base polymer. Solubility is the key to understanding processing promoters. If the chemical is very soluble in the polymer, it dissolves fast, opens the polymer network, and allows faster filler incorporation. The chemical then remains in the bulk of the polymer matrix affecting the viscosity of the compound. On the other hand, if the processing promoter has limited solubility in the polymer, or contains components that have limited solubility in the polymer, then that insoluble portion can bloom to the surface of the rubber stock or to the interface between the rubber and the surfaces of the processing equipment. This gives a lubricating effect between the rubber stock and the parts it contacts, such as metal surfaces of the mixing equipment, extruder dies, injection molding mold surfaces, calender rolls, etc. Thus, the portion of the processing promoter that blooms to the surface acts as an external lubricant. The portion that dissolves in the rubber stock behaves as an internal lubricant and reduces the viscosity. The combined effect of lower viscosity and greater surface lubricity has a pronounced effect on flow properties.

Advantages of using dispersants or internal lubricants include:

* Reduced mixing time;

* improved carbon black/filler dispersion;

* improved dispersion of curatives;

* improved batch-to-batch consistency;

* reduced compound viscosity;

* improved flow characteristics of the compound.

Figure 2 clearly shows the advantages of using a good dispersing agent such as a polymer soluble zinc soap of predominantly unsaturated fatty acids.

[GRAPH OMITTED]

It was the custom at a certain rubber company to run a rheometer curve on each batch of stock mixed in the internal mixer. At the end of each shift, all of the rheometer curves would be printed on a single sheet of paper. The set of 25 curves you see at the top are from a period of time when the stocks were mixed without a processing promoter.

The set of 25 rheometer curves on the bottom was made after the company started using a processing promoter composed of zinc soaps. This shows a rather dramatic difference in batch-to-batch consistency.

This obvious improvement in batch-to-batch consistency provides a number of downstream advantages.

External lubricants offer the following advantages:

* Higher extrusion rates;

* constant extrusion temperature;

* lower energy consumption;

* extrusions free of pulsations;

* higher dimensional stability;

* little decrease in viscosity;

* smoother surfaces.

Table 8 shows a couple of practical examples in which the differences between dispersants and lubricants can clearly be seen. Figure 3 is a comparison between Aflux 12, which has very limited solubility in NBR, and Aktiplast T, a soap, which is totally soluble in NBR. In this example, the Aflux 12 generates an incredible surface lubrication resulting in greatly increased injection molding speed and a much higher loading of the injection spider mold. Aktiplast T, which is totally soluble in NBR, also provides a slight improvement in flow properties over the control, partly due to some of the material being on the surface and partly because of the reduced viscosity of the compound. However, because of its greater solubility in the rubber matrix, it cannot give the same improvement in flow properties as obtained with the Aflux 12.

[ILLUSTRATION OMITTED]

Table 8 - internal versus external lubricants in
NBR

Recipe:
Perbunan N 3307                   100    100    100
Carbon black N-550                 65     65     65
Vulkanol 85                        10     10     10
Stearic acid                      0.5    0.5    0.5
Vulkanox HS                       1.5    1.5    1.5
Vulkanox MB 2                     1.5    1.5    1.5
Zinkoxyd Aktiv                      5      5      5
Sulfur                            0.4    0.4    0.4
TMTD                              2.5    2.5    2.5
Aktiplast T                        --      3     --
Aflux 12                           --     --      3

Mooney viscosity ML(1+4) 100
  [degrees] C                      85     80     70

Physical properties (cured 10'
  @ 160 [degrees] C)
Hardness (durometer A)             73     70     70
Elasticity (%)                     31     30     30
Tear strength (N/mm)             24.4   22.9   27.2
100% modulus (MPa)                4.9    4.1    4.3
300% modulus (MPa)               16.3   13.6   13.8
Tensile strength (MPa)           19.8   20.1   19.1
Elongation at break (%)           400    500    435

Extrusion speed (cm/min.)         118    140    144
Extrusion output(g/min.)          100    125    140

Rheovulkameter (180 [degrees]
  C/50s/80 bar)
IM volume ([mm.sup.3])            305    580    863
IM speed ([mm.sup.3]/s)          11.3   16.5   24.5

One point worth mentioning is that the tensile strength values have been maintained throughout the entire gamut of the test series, and percent elongation at break values have only slightly changed with the increased levels of plasticizer. If these changes are unsatisfactory, they can be restored by simply removing some of the plasticizer.

The most important point to remember from the above discussion is that a processing promoter can behave as an internal lubricant (dispersant) in one polymer and as an external lubricant (lubricant) in another. Thus, it is extremely important to know the nature of the compound you are using and the properties you wish to influence before selecting the processing promoter.

Homogenizers

Processing promoters that function as homogenizers are composed of chemicals that are compatible with polar and nonpolar polymers. The most efficient homogenizers are typically resins containing aromatic, naphthenic and paraffinic fractions. These processing promoters, when added to a blend of two dissimilar polymers, become the common solvent, if you wish, and thus allow more intimate mixing of the two different polymer phases within the mix. Because of their solubility in the polymers, as you would expect, they greatly improve filler dispersion, especially carbon black dispersion. One can achieve a comparable degree of homogenization by using a blend of processing promoters, each being soluble in one of the polymers to be blended, but then there is the risk of blooming.

The most common homogenizing agents include low molecular weight resin blends, fatty acid derivatives and products based on bitumen. A graphic example of a homogenizing processing promoter at work can be seen in the electron microscope pictures of an NR/SBR/BR blend with and without the homogenizing agent Rhenosin TP 100 in figure 4. The large color variation in the first picture indicates areas of unmixed polymer phases, while the uniform color in the second picture indicates good homogeneity of the mix.

[ILLUSTRATION OMITTED]

Misconception

Some people believe that a simple process oil can be used as a process promoter. This is a misconception. The data in table 9 distinguish rather dramatically the differences between a processing promoter and a process oil. Process promoters do function as plasticizers, whether you like it or not; however, they provide properties that a process oil cannot provide.

Table 9 - comparison between plasticizer and
process promoter

Compound                              165.9       165.9
Naphthenic oil                         13.0        10.0
Aktiplast T                              --         3.0
                                      178.9       178.9
Mooney ML (1+4) 100 [degrees] C          37          37
Mooney scorch 120 [degrees] C
t5-min.                               40:39       39:22
t35-min.                              45:05       43:23

Vulcanizate 150 [degrees]
  C/20 min.
Hardness - durometer A                   53          59
Modulus - MPa
100                                     1.5         1.9
300                                     6.0         9.0
500                                      11          16
Tensile - MPa                            20          24
Elongation - %                          830         690
Tear- N/mm                               69          58

Compression set - %
168 h./70 [degrees] C                    55          42
24 h./70 [degrees] C                     34          25
24 h./RT                                 16          15

Hot air aging - 7d/70
  [degrees] C
Hardness - ShA                        57 +4        60+1
Modulus - MPa
100                               1.8 + 20%   2.3 + 21%
300                                12 + 53%     10 + 9%
500                                22 + 73%     17 + 3%
Tensile - MPa                      25 + 10%   23.5 - 2%
Elongation - %                    580 - 37%    685 - 1%
Tear - N/mm                        50 - 28%     57 - 3%

Rheovulcameter (100 [degrees]
  C/150 [degrees] C mold)
Volume - ccm                          1,930       2,165
Velocity (max.) - ccm/sec.               86          99

To demonstrate this phenomenon, we very conservatively used 13 parts of a naphthenic oil in the control stock and a comparison stock in which we replaced three parts of the oil with a zinc soap. As we look at the data, we see that the Mooney viscosity and Mooney scorch are the same, so you can say that the processing promoter behaved as a process oil. The rest of the data, especially the modulus, as you may expect, is a lot higher because of the lower oil content. But due to the increased solubility of the zinc soap, some of this improvement is due to a much tighter rubber matrix. The tensile strength inevitably increases and percent elongation at break inevitably decreases due to better carbon black dispersion. The compression set values are much lower compared to the control stock. And last, but not least, if you look at the aging characteristics between the control stock and the one containing less oil and the processing aid, you see an astounding difference. The compound with all oil ages poorly, which would indicate an obvious problem with the comly, which would indicate an obvious problem with the compound.

Looking at a few specific properties, specifically the aging performance of the elongation, there is a difference of 37% for the oiled stock versus a 1% change for the stock mixed with the processing promoter. This is a significant difference. The differences in processability are nicely demonstrated in the injection molded volume. The stock with the processing promoter shows more than a 10% improvement over the other. Since this compound is a lot tougher, you would expect that it would be more difficult to process, but the reverse is true.

Summary

Processing promoters can provide dramatic improvements in mixing and processing of rubber compounds. The goal is to select the correct processing promoter to achieve the desired results, which is based on the properties to be changed and the base polymer of the compound.

The four basic categories of processing promoters are peptizers or mastication aids, internal lubricants or dispersants, external lubricants and homogenizers. The solubility of the processing promoter in the base compound determines how it will function in that compound, either as a dispersant or lubricant.

Processing promoters that are composed of several chemicals will perform the various functions to the extent of solubility and percent of each component in the base compound.

Processing promoters should be added at the correct time in the mixing cycle to achieve maximum results. Peptizers are commonly added at the very beginning with the polymer. Dispersants are to be added with the fillers. Lubricants can be added even later in the mix cycle.

Processing promoters can have an effect on Mooney scorch, t2 and t90; therefore, processing promoters should not be treated as simple additives to an existing compound, but rather, should be considered critical ingredients.