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塑解剂:一个比较新的概念  发帖心情 Post By:2007/10/31 22:18:00 [只看该作者]


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Save time and money with peptizers

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Michel BIRON

Introduction
What are the peptizers?
Peptizers : for what rubbers ? and sometimes for thermoplastics also?
Peptizers: homeopathic additives
Inhibiting effects of other additives
Peptizers: The panacea? Yes and no, because of possible collateral effects
Top-of-the-range solution: proprietary zinc-free combinations of chemical and physical peptizers plasticizing in 75 seconds
Peptization of thermoplastics: example of polypropylene viscosity breaking
Conclusion

 Introduction

Originally, rubbers are independent macromolecular chains with poor characteristics and it's essential to incorporate numerous additives into them, currently 10 up to 15, during a mixing process to subsequently promote crosslinking, reinforcement, ageing protection... Sometimes the molecular weight of the elastomer, specially the natural rubber, is so high that too difficult and expensive is the incorporation of additives. The only solution is to masticate the rubber in presence of the oxygen of air by mechanical breaking and oxidative scission of the macromolecular chains. The process is time, energy and money consuming. To speed it, it is possible to use chemical additives or peptizers, which promotes the reduction of the elastomer molecular weight by chemical means thus increasing the efficiency of rubber mastication. That results in reduced viscosity and nerve thus improving the processability of the polymer.

The following figure 'Mechanical-Mastication-versus-Chemical-Peptizing' compares the dump times and temperatures, the energy consumption for the same reduction of the consistency of the same rubber. We can remark the drop in mastication time and energy consumption and the correlative reduction of the dump temperature, which is of a great interest for the addition of curing additives.

图片点击可在新窗口打开查看
Mechanical Mastication versus Chemical Peptizing

Generally speaking, peptization is defined as the dispersion of a substance into a colloidal state, usually to form a sol. For polymers, the signification is extended to the controlled scission of macromolecular chains to obtain a lower viscosity improving the process ability.


 Superabsorbent polymers - SAP: An explosive market growth

Many chemicals are able to shorten the macromolecules but to be industrially efficient it is essential that they don't produce detrimental collateral effects such as early ageing or curing disturbance. Among them we can notice:

  • Di-benzamide-diphenyl-disulphide,
  • Pentachlorothiophenol and its derivatives,
  • Nitrosocompounds,
  • Mercaptans and their zinc salts,
  • Thiocarboxylic acids and their salts,
  • Sulphenamides,
  • Hydrazines,
  • TETD, tetraethylthiuram disulfide in sulfur-modified polychloroprenes
  • Perkacit TMTD
  • Q-Flex QDI

To optimize their efficiency, peptizers can be coupled with boosters or catalysts, such as, for example:

  • Peroxides and metal complexes, having depolymerizing effects depending to a large extent on the structure of the radicals
  • Dibenzamidodiphenyl disulphide and complex iron compounds
  • Pentachlorothiophenol or the corresponding zinc salt and proprietary boosters
  • Iron, cobalt, nickel or copper complex
  • Phthalimide
  • Organic metal chelate
  • Proprietary combinations such as Renacit 8 (B 300)

The following figure 'Viscosity-versus-Storage-Time' compares the immediate and long-term efficiency of a peptizer and a combination peptizer/booster. We can remark the high drop of viscosity, about 33% with the peptizer alone and the extra decrease when the booster is added to the peptizer.

图片点击可在新窗口打开查看
Viscosity versus Storage Time

As already said, peptizers are used in combination with numerous other additives that can interact. Some peptizers are especially dedicated to applications in the presence of specific additives. For example, Renacit® 11 and Renacit®11/WG, by LANXESS offer high performances in the mastication of natural rubber in the presence of carbon black.


 Peptizers : for what rubbers ? and sometimes for thermoplastics also?

Natural rubber is the most often peptized but other rubbers can be depolymerized such as, for example SBR, polychloroprene, nitrile butadiene rubber (NBR ), butyl rubber (IIR ) etc. Concerning thermoplastics, polypropylene can be depolymerized with a very low level of peroxide.


 Peptizers: homeopathic additives

Peptizers are used at very low dosages, 0.05 up to 0.3% for example, and it is necessary to watch over:

  • The accuracy of dosing
  • A fast and efficient dispersion and distribution.

The accuracy of dosing can be obtained using an additive with a low level of active material. For example, LANXESS proposes its Renacit® RUC 9205 having an active ingredient content of 8 % and that can be metered at correspondingly higher concentrations. This improves the weighing accuracy, and, as a result of the higher weighed portion, a more homogeneous distribution of the peptizing agent can be achieved (thereby avoiding "hot spots"). Tests confirm this.

For a fast and efficient dispersion and distribution, chemical peptizers can be combined with physical peptizers or processing aids. Physical peptizers are, for example, blends of zinc salts of medium to higher molecular weight fatty acids. They ensure a much faster incorporation and a better distribution of the peptizer, easing the dispersion of the chemical peptizer, helping to overcome the problems of hot spots and improving batch to batch uniformity.


 Inhibiting effects of other additives

Peptizing effect can be inhibited by common additives such as:

  • Sulphur
  • Carbon black
  • Thiurames
  • Guanidine
  • Zinc oxide
  • Phenylene diamine...

In systems without fillers these chemicals act virtually as stoppers of peptizing agents. For this reason, it is preferable to add the peptizer to the rubber at a very early stage of manufacture to break down rapidly the rubber during the mastication step. If it is not desired, some peptizers are designed to be used in the presence of carbon black. For example, Renacit® 11 and Renacit®11/WG, by LANXESS offer high performances in the mastication of NR.


 Peptizers: The panacea? Yes and no, because of possible collateral effects

Chemical peptizers are oxidative catalysts of various structures and it is obvious that they can act on end properties of rubbers. As they catalyze the oxidative chain splitting, it is obviously conceivable that the chemically accelerated depolymerization could affect the properties and durability of the vulcanizates. This point must be examined with a special attention concerning the immediate and long-term effects.

Peptizers are commonly used in tyre industry but their choice must take into account two important features:

  • If the efficiency of chemical peptizers is high, they also produce a lot of short chains resulting in poorer dynamical properties.
  • The combination of chemical peptizers and physical ones lead to an appreciable amount of zinc considered as a hazardous element and subjected to constraints militating for its ban.

Table 1 shows the molecular and end properties obtained by using various chemical peptizers to produce a tyre compound based on natural rubber. For each property, results are expressed as the percentage of the value obtained with peptizer versus the value obtained by mastication during the same time without peptizer. Thus, the elastic modulus after ageing is the percentage of the value obtained with peptizer versus the value obtained by mastication without peptizer.

The molecular weight and the consistency are markedly decreased when the gel content is slightly reduced. The Goodrich test is detrimentally affected with a higher heat build-up temperature and a lower blow-out temperature. Dynamic properties are diversely affected particularly after ageing.

Less than 100
Higher than 100
Molecular properties
Molecular weight
65-70
Gel content
83-92
Consistency (ML 1+4)
50-75
Goodrich temperatures
Heat build-up
105-110
Blow out
90-92
Dynamic properties
Elastic modulus
105-108
Viscous modulus
111
Tangent delta
96-99
100-104
Loss compliance
83-91
Dynamic properties after ageing
Elastic modulus
104-114
Viscous modulus
107-121
Tangent delta
104-109
Loss compliance
85-92
Table 1: Properties obtained by using various chemical peptizers. Results are linked to those obtained by mastication

To overcome these problems and environmental constraints, new generations of zinc-free peptizers are designed to preserve the dynamic properties.


 Top-of-the-range solution: proprietary zinc-free combinations of chemical and physical peptizers plasticizing in 75 seconds

Table 2 shows the rheological and end properties obtained by using a proprietary zinc-free combination of chemical and physical peptizers needing as little as 75 seconds for the mastication of natural rubber to produce a tyre compound. For each property, results are expressed as the percentage of the value obtained with peptizer versus the value obtained by mastication during a sufficient time to obtain the same consistency without peptizer. Thus, the elastic modulus after ageing is the percentage of the value obtained with peptizer versus the value obtained by mastication without peptizer. These data are not comparable with those of the table 1 because of the adjustment of the mastication time to obtain the right consistency. We can notice the productivity enhancement due to the high extrusion speed without heat build up.

Rheological properties
Torque ML
97
Torque MH
101
Tc 10%
91
Tc 90%
92
Tc 100%
92
Tan delta
114
Reversion t95%
93
Mechanical properties
Hardness
101
Tensile strength
100
Modulus 100%
104
Modulus 300%
105
Elongation at break
97
Rebound
98
Abrasion loss
103
Properties after ageing
Hardness
100
Tensile strength
99
Modulus 100%
103
Modulus 300%
99
Elongation at break
101
Rebound
95
Extrusion
Rubber temperature
100
Screw speed
150
Output
149
Profile speed
145
Die swelling
103
Profile aspect
100
Table 2: Properties obtained by using a top-of-the-range peptizer Results are linked to those obtained by mastication

The results obtained with peptizer and mastication are similar as we can see on the following figure 'Frequency-Curve-of-Linked-Properties' plotting the frequency of the linked property data centred on 100 (equal properties) with most values in the range from 93 up to 107.

图片点击可在新窗口打开查看
Frequency Curve of Linked Properties

 Peptization of thermoplastics: example of polypropylene viscosity breaking

The peptization of polypropylene is commonly applied by reactive extrusion in the presence of very low levels of an organic peroxide. This one, as we can see on the following figure 'Principle-of-Viscosity-Breaker-Action' leads to the scission of polypropylene chains.

图片点击可在新窗口打开查看
Principle of Viscosity Breaker Action

The following figure 'Examples-of-viscosity-versus-peroxide-level' shows the effect of the percentage of peroxide on the viscosity of a same polypropylene treated with two different peroxides.

图片点击可在新窗口打开查看
Examples of viscosity versus peroxide level

Unfortunately, peroxides can lead to two types of collateral effects:

  • They can reduce the thermal and colour stability of the polypropylene and interfere with stabilisers protecting the polymers from free radical attacks. This is why it is strongly recommended to incorporate at first the peroxide and then the additives in a second step when most of the peroxide has reacted. Furthermore, an efficient stabilisation system is required.
  • After decomposition, the peroxide residuals can interfere with other additives such as nucleating agents and can have negative impact on final properties, long term ageing, organoleptic characteristics, odour, FDA approvals...

 Conclusion

To allow the incorporation of the additives needed for the optimization of end properties or to allow processing it can be necessary to decrease the viscosity of polymers by breaking the macromolecules. The basic solution is to masticate the rubber in presence of oxygen but the process is time, energy and money consuming. Peptizers are additives especially designed to control oxidative scission, speeding up the process and saving costs.

Top-of-the-range proprietary zinc-free combinations of chemical and physical peptizers can plasticize natural rubber in very short times as low as 75 seconds without significant degradation of end properties and ageing resistance.

This technique is also adaptable to thermoplastics such as polypropylene peptized with peroxides. Unfortunately, the peroxide structure can affect the processing and the end properties, the ageing behaviour and the service properties. As a result, selection must be careful, taking into account the targeted application of the polypropylene parts.


 References

Technical books and guides, papers, websites: Akrochem, BASF, Bayer, BP, Ciba, COMAIP, Crompton, Dow, Flexsys, FPI Flow Polymer Inc, IFOCA, Kaouchem, Lanxess, Rhein Chemie, Röhm GmbH, Schill + Seilacher Struktol, SpecialChem...

V. Subrahmanian and ALL (Rubber World, April 2006, p.37)
H. Azizi and ALL (Iranian Polymer Journal, 14, 2005, p. 465)
M. Henzel and ALL (KGK, 57, 3, 2004, p.95)
K. Menting and ALL (ACS, Rubber Division, April 2003, paper 70)
L. Steger and ALL (ACS, Rubber Division, April 2003, paper 46)
F. Ignatz-Hoover (ACS, Rubber Division, April 2003, paper 11)
F. Ignatz-Hoover (ACS, Rubber Division, October 2002, paper 106)
C.R. Stone and ALL (Tire Technology Intern. 1998, p.68)

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  发帖心情 Post By:2007/10/31 22:19:00 [只看该作者]

物质性质信息

名称催化剂型增塑剂;peptizer;peptizing agent
资料
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分子式:
分子量:
CAS号:

性质:又称塑解剂。对橡胶有解聚作用而使橡胶塑化和使橡胶烃与氧作用的增塑剂。用量少而效力大,好像是催化剂。能缩短塑炼时间。它对硫化胶的力学性质没有明显的影响。其作用机理是本身受热后在氧作用下产生游离基,使橡胶大分子裂解;或能封闭塑炼时生胶分子链断链产生的端基,使其失去活性并不再重聚。一般除用于生胶塑炼外,还可用作再生胶再生活化剂。用后不影响胶料的硫化速度和硫化胶的物理机械性能。有低温塑解剂和高温塑解剂之分,前者有苯醌和偶氮苯,后者有过氧化苯甲酰与偶氮二异丁腈。


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  发帖心情 Post By:2008/2/12 18:52:00 [只看该作者]

very thank you

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