Additives are used to provide and/or modify some properties of PVC.
PVC is the most compounded plastic, and for this reason has to be considered as the most versatile plastic. From rigid pipes to synthetic leathers, products based on PVC and additives show tailor made properties that allow their use in a huge range of markets and applications.
Among the most usual additives, we can mention: stabilizers, lubricants, fillers, processing aids, impact modifiers, plasticizers, pigments, etc…
As you know the REACH Regulation is entered into force since 1st of June 2007.
PVC is a polymer and even though polymers are in the scope of REACH, they are exempted from the registration and evaluation processes.
By contrary, the monomers and other substances that are covalently bound into the final polymer are subject to the standard registration process.
You will find here a useful site where you can find some guidance about REACH regulation: http://reach.jrc.it/
a. Stabilisers
1. Are there still heavy metals used for the stabilisation of PVC?
2. Heavy metals are used as heat stabilisers to allow PVC to be moulded into products. Some of them are known to be dangerous. How can you defend the use of such dangerous material?
3. Which precaution must be taken to use lead stabilisers?
b. Lubricants
4. What are the effects of the internal lubricants?
5. What are the effects of the external lubricants?
6. Which modification of the lubrication can I do to reduce plate out?
7. How can I reduce the shrinkage of the profiles?
c. Fillers
8. What are the reasons to use fillers?
9. What is the difference between natural and precipitated Calcium Carbonate?
d. Processing aids
10. What are the reasons to use processing aids?
e. Impact modifiers
11. Which are the different impact modifiers on the market?
f. Plasticisers
12. What are plasticisers?
13. What are phthalates?
14. Are phthalates carcinogenic?
15. Recent reports suggest that plasticisers used in PVC disrupt the human hormone system and can reduce sperm counts. Are we sure that plasticizers do not cause reproductive health problems?
16. Why have some phthalates been banned from use in toys in the EU?
g. Pigments
17. Which kind and which quantity of TiO2 do I have to use to achieve good outdoor weatherability of profiles?
h. Others
18. Which additives can be used for better flame resistance of articles?
19. How can I improve the thermo mechanical resistance of PVC by special additives?
20. How is it possible to achieve transparent and impact resistant PVC profiles?
a. Stabilisers
1. Are there still heavy metals used for the stabilisation of PVC?
In Europe, the Cadmium (Cd) is not used anymore. It has been forbidden since 1990. The Lead is still used but despite the fact that Lead stabilizers don’t give any health or/and environmental problems when incorporated in finished products, the PVC industry has established a Voluntary Commitment called Vinyl 2010 which stated that the use of lead stabilizers must be reduced by 50% in 2010 and 100% in 2015.
2. Heavy metals are used as heat stabilisers to allow PVC to be moulded into products. Some of them are known to be dangerous. How can you defend the use of such dangerous material?
Substances based on certain metals are used in PVC compounds as stabilisers. In use, these materials are sealed into the polymer matrix and represent no danger to public and environmental health. Nevertheless, Vinyl 2010 has committed to phase out the Lead stabilisers for 2015.
When evaluating the environmental consequences of these stabilisers, one has to consider both the amount of the stabiliser which might migrate from the plastic into the environment, and its toxic potential. Research has shown that whilst migration of these compounds is possible, only a small proportion of the stabiliser will leach out of the plastic during its service life.
The use of all stabilisers is also closely regulated and, in critical applications of PVC compounds, such as in toys, food contact, potable water and medical devices, there are detailed regulatory controls with positive lists of allowed material. For theses sensitive applications, calcium/zinc and organotin compounds are used.
3. Which precaution must be taken to use lead stabilisers?
In general, exposure is controlled by modification of the equipment, implementation of adequate ventilation, wearing of personal protection equipment to avoid the emission of dusts, clothes and gloves, workplace cleaning and observance of high personal hygiene standards.
It is recommended to avoid the exposure of the workers to a dust of Lead stabilisers by using non dusty physical presentations.
(Source: ESPA: www.stabilisers.org)
b. Lubricants
4. What are the effects of the internal lubricants?
The internal lubricants are compatible with the PVC and that will give them a certain solubuility into the PVC particles. They reduce the Van der Waals forces between the PVC chains and thereby the viscosity of the melted phase and the head pressure.
They have no significant effect on the fusion behaviour and the clarity of the PVC formulations.
5. What are the effects of the external lubricants?
The external lubricants are relatively incompatible with the PVC and will not penetrate into the PVC particles. They decrease the friction between PVC grains and prevent the sticking of the melted PVC on the hot metallic surfaces. They allow the control of the gelation into the machine by decreasing the head pressure and the gelation speed of the PVC chains. At a certain level, they affect the clarity of the PVC formulations.
6. Which modification of the lubrication can I do to reduce plate out?
The plate out on the extrusion tools is often generated by an excess of external lubricants into the PVC formulation. The optimisation of the lubrication with a reduction of the incompatible external lubricants and the use of more compatible lubricants with good metal release properties can bring a significant plate-out reduction.
7. How can I reduce the shrinkage of the profiles?
To reduce shrinkage, the lubrication must be increased; internal lubrication to reduce head pressure and external lubrication to facilitate metal slipping.
A reduction of the swelling by decreasing the content of acrylic Processing-aids or by increasing the filler content can also bring some improvements.
c. Fillers
8. What are the reasons to use fillers?
They increase the rigidity and facilitate the gelation.
The fillers can in some cases (wood fibres, glass fibres) give special characteristics to the final product (appearance, extremely high rigidity, fire resistance).
Another reason is also to decrease the price of the formulation as the most commonly used fillers (natural Ca Carbonate) are cheaper than PVC.
The cost advantage must be considered in volume in most of the cases and, in that case, the difference of density between PVC and Calcium Carbonate must be taken into account. The density of the Ca Carbonate is about twice the density of PVC.
9. What is the difference between natural and precipitated Calcium Carbonate?
The main difference is the dimension of the grains. In the case of natural CaCO3 (NCC), the average particle size d50 is between 0.5 and 5 µm. In the case of precipitated CaCO3 (PCC), the average particle size is generally below 0.1µm. The PCC has a positive effect on the gelation speed, the impact strength and the gloss.
d. Processing aids
10. What are the reasons to use processing aids?
The acrylic processing aids have an effect on the gelation speed and the gelation level. They increase the melt strength and melt elongation. They are particularly used for expanded PVC applications because they avoid the collapsing of the cells. They reduce the surface defects in extrusion, in calendering and in injection moulding.
e. Impact modifiers
11. Which are the different impact modifiers on the market?
The acrylic impact modifiers (butyl or ethyl heryl acrylates) are used in window profiles, shutters and some pipe applications with high impact requirements.
The chlorinated PE can also be used. The MBS or the ABS have better impact properties but can only be used for indoor applications as the butadiene has a poor UV resistance.
f. Plasticisers
12. What are plasticisers?
Plasticisers are substances which are incorporated into PVC in order to make the finished products soft and rubbery.
They have very high compatibility with PVC and reduce the friction between PVC molecular chains.
13. What are phthalates?
Phthalates are a large variety of plasticisers used for softening the PVC products. They are colourless, viscous liquids with little or no odor and low volatility.
14. Are phthalates carcinogenic?
No phthalates are classified as human carcinogens by the World Health Organisation (WHO) and there is no evidence to suggest that phthalates can cause cancer in human beings. Since 1980 a large number of investigations have shown that feeding high levels (many thousand times greater than foreseeable exposure) of phthalates and other chemicals to rodents over their lifetime causes a large increase in microbodies in the liver called peroxisomes. This 'peroxisome proliferation' leads to the formation of liver tumours. However, when these chemicals are given to non-rodent species such as marmosets and monkeys (primates considered to be metabolically closer to humans), such peroxisome proliferation and liver damage is not seen.
On the basis of these differences in species response, it was concluded some years ago that phthalates do not pose a significant health hazard to people. This scientific view was adopted by a European Commission decision of 25 July 1990 which states that DEHP shall not be classified or labelled as a carcinogenic or irritant substance. The correctness of this decision has recently been reaffirmed by two comprehensive reviews.
In February 2000, the International Agency for Research on Cancer (IARC) - which is part of the World Health Organisation (WHO) - re-classified the phthalate plasticiser DEHP as "not classifiable as to carcinogenicity to humans."
(Source: Phthalates Information Center Europe: www.phthalates.com)
15. Recent reports suggest that plasticisers used in PVC disrupt the human hormone system and can reduce sperm counts. Are we sure that plasticizers do not cause reproductive health problems?
It has been hypothesised (and at the moment it remains a hypothesis) that some reported cases of reduced sperm count in men may be due to exposure to chemicals in the environment which mimic the natural female hormone oestrogen. There is still no evidence that there is a general problem in humans and no evidence that chemicals in general, or any chemicals specifically, are the cause. However, this hypothesis has sparked interest in the development of screening tests which could be used to identify oestrogenic substances.
The potential reproductive risk posed by some phthalate esters has recently been reviewed by the Commission of the European Communities. While it is the case that some phthalates have been shown to cause reproductive effects in rats and mice, these have occurred at levels 10,000 times higher than the estimated exposure to people. It is, therefore, very unlikely that any significant risk to human reproductive health is associated with the use of phthalates.
The hypothesis of the potential impact of industrial chemicals on animal and human health and fertility is, in fact, a question for the entire chemical industry. Cefic, the body which represents the European chemical industry, has responded to this broad debate and has already implemented a substantial program of research.
(Source: Phthalates Information Center Europe: www.phthalates.com)
16. Why have some phthalates been banned from use in toys in the EU?
The European legislature voted to pass that ban, even though the draft conclusion of an exhaustive safety review of the principal phthalates used in toys stated it was “unlike to pose a risk”, even for newborns. In other words, it was a political decision based on the precaution principle, not a regulatory one based on scientific evidence.
g. Pigments
17. Which kind and which quantity of TiO2 do I have to use to achieve good outdoor weatherability of profiles?
The TiO2 must be of the rutile type. For Europe, the grade must not be too photoactive.
The quantity depends on the climate. For the North of Europe, a minimum amount of 4 phr is recommended, for the South of Europe, a minimum of 5 phr is recommended. For very hot and dry climates, 6 to 10 phr could be requested.
h. Others
18. Which additives can be used for better flame resistance of articles?
The most used additive is the Antimony Trioxide (Sb2O3) but it requires special protection equipment for the handling and mixing. It’s one of the most efficient additives to reduce heat release and propagation of fire but it increases the smoke release.
Aluminum trihydrate (ATH) and Magnesium Dihydrate (MDH) are also used to reduce heat release and smoke production. They are efficient additives but must be used at higher amount (10 to 20 phr).
In soft PVC, the phosphate plasticizer is also efficient to improve reaction to fire.
There are also other additives that are proposed: Zinc Borate, Aluminum Octamolybdate, Molybdic oxide and Zinc Hydroxystannate.
19. How can I improve the thermo mechanical resistance of PVC by special additives?
Alloys of PVC with high temperature resistant polymers are possible. For example, polymers based on Styrene could be used (ABS, AMSAN, ASA).
20. How is it possible to achieve transparent and impact resistant PVC profiles?
The PVC polymer is instrinsically transparent.
The use of special types of additives like MBS impact modifiers allow the production of transparent and impact resistant PVC profiles.
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