Safety/Toxicity

INTRODUCTION

Globally, the rubber industry has been very active in its social commitments to control the adverse effects of chemicals, hazardous to the human body.

As a consequence of this several rubber chemicals have been removed from the market:

  • Phenyl Alfa Naphthlylamine
  • Phenyl Beta Naphthylamine
  • DPPD
  • IPPD
  • Nitroso compounds
  • Isocynate type bonding agents
  • Morpholine derivatives in the class of sulphenamides
  • And many others

At Solidite we have implemented many of the Safety and Toxicity guidelines produced by the following organizations:

  • EU associations and related authorities.
  • FDA from USA
  • Other pollution control and health protection authorities also from India, Korea and Japan.

Solidite is committed to Safety and Toxicity throughout all of our manufacturing processes:

  • Solidite respects and conforms with the Global Commitment to environmental safety and health hazards.
  • The Solidite range of solid cushioned and Press On Band tyres when mounted on prescribed rims will fit, without slip, thereby not contributing to vibrations.
  • Solidite have chosen Noise Reduction and suitable cushion compounds to minimize vibrations and improve damping.
  • All known chemicals hazardous to health, including Aromatic oils, have been removed from Solidite formulations since December 2008.
  • In Non-Marking tyres, Solidite use only chemicals that are within usage limits cleared by FDA (USA) in rubber products that come in long or continuous contact with food products.
  • Solidite tread formulations are designed to offer best wet-skid resistance.
  • Solidite R&D has many programmes in hand to serve to global needs.

SOLIDITE R&D PROGRAMMES

The focus of Solidite for their R&D programme was mainly based on:

  • Physical factors like vibrations, wet skidding etc.
  • Influence of micro-fine carbon black during mixing,
  • Health hazards like suspected carcinogenic and other harmful materials.
  • Selection of rubber chemicals in products that come in contact with food products.
  • (Non – marking solid cushioned tyres).

Generally vibrations are developed by high speed movement. If contribution from tyres has to be considered, tyres begin used at speed are generally more vulnerable to increased vibrations or will contribute adversely to the vibrations created by the vehicle itself.

Slow moving tryes like Solid Cushioned tyres or Press on Band tyres significantly reduce vibrations (These tyres are designed to run at low speed and on indoor pavements). Fork-lift and industrial tyres have a maximum speed limit of 25 km/hour.

Using EU Directive 2002/44/EC- “on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration)” of the European Parliament and the Council , Solidite undertook a programme to ensure that no slippage takes place when Solidite Solid Cushioned tyres are fitted onto the recommended rims.

CARBON BLACK PARTICLES

Micro fine particles of carbon black are yet another health hazard when carbon mixing is done on open mills. To solve these issues, Solidite adopted two systems.

  • Use of carbon black master batches where carbon blacks are mixed in rubber at the latex stage and
  • Use of internal mixers like Banbury, Intermix or a Kneader; with chemical aid for dispersion.

CHEMICALS AND HUMAN HEALTH

Substantial quantities of OE – Extended Polybutadiene were used to achieve good abrasion resistance, but this also developed low wet skid resistance. Experimentation led to Solidite removing Polybutadiene and still being able to achieve the required level of abrasion resistance by using finer particle sized carbon blacks and special usage of precipitated silica. This was possible only because the maximum speed for Solid Cushioned and Press on Band tyres is limited to 25 km/hour.

Chemicals that were constituted as health hazards were replaced by chemicals that are safe.

And finally, in the non – marking tyres only such chemicals were used in formulations that are cleared by FDA of USA for use in articles coming in long or continuous contact with food products.

VIBRATIONS AND HUMAN PERCEPTIONS

Dropping every synthetic rubber and opting only for (Natural Rubber) in the Solid Cushioned Tyres of Solidite is not by default but by design.

The choice of Natural Rubber to reduce vibrations and shocks is fully supported by authentic technical literature. To quote just one reference we would like to highlight pages 28 and 29 of Hoffmann Rubber Technology Handbook that says–

“ The favourable elastic properties manifest themselves in very low damping (low hysteresis) and a low heat build-up in dynamic deformations. This behaviour combined with very short relaxation times, qualify NR especially for products which function in dynamic applications. These include vibration and suspension elements and tyres. The dynamic fatigue resistance of NR vulcanizates is also excellent”.

Solidite use only Natural Rubber as the basic polymer in their compounding of components for solid cushioned tyres.

Fast moving objects create vibrations. An engine creates vibrations. Rubber components like “Vibra-mounts” are fixed into the vehicle systems to ensure that vibrations created by the engine do not reach the vehicle passengers. Rubber based “Vibra-mounts” thus help damping. Typically the engine mountings or vibramounts are a sandwich of a rubber cured compound between two metal plates with solid bonding between metal and rubber.

Tyres, whether pneumatic or solid have a component called cushion which is sandwiched between tread and core, both much harder compared to cushion.

Load – Deflection curves indicate quality norms of cushion. The Lower the deflection the better the vibration damping properties but the load carrying capacity is reduced.

Solidite have fixed minimum and maximum levels of deflection that allows the tyre to meet ETRTO load specifications;

  • ‘a’ is the toughest tyre.
  • ‘f’ is the softest tyre.
  • b,c,d,e will depend on cushion (and obviously the required damping effect)

a>b>c>d>e>f for Load Bearing Capacity and

f>e>d>c>b>a for cushioning effect. ( > means “better than” )

An Interesting study of vibrations effect on humans is correctly exhibited by Reiher – Meister scale of human perception of vibrations (Fig. 2). Consider only solid cushioned tyres the best contribution from tyres will come when –

  • Deflection (in load – deflection curves) is lowest and
  • Tyres fit into rims without slip.

Solidite have mastered rubber technology that can provide any level of deflection within limits of loads specified by ETRTO and also ensure fitment of tyres into rims without slip.

(Frequency is in cycles per second)

  • a – Imperceptible
  • b – Just perceptible
  • c – Easily Noticeable
  • d – Annoying
  • e – Unpleasant
  • Beyond e – Painful (Dangerous for short period)

As per EU Directive every work location has to select levels of damping to ensure that finally transferred vibrations are within specified limits. Solidite can help in selection of Load – Deflection curve for a given solid tyre size.

VIBRATION CONTROL

Contribution to vibration can be controlled or totally eliminated by ensuring that the grip of tyre bead zone into the rim is perfectly satisfactory and shows no slip when the tyres are run with maximum specified loads at maximum permissible speed on a good concrete pavement.

This was achieved by creating compression in the bead zone, both vertically and laterally.

Lateral compression was achieved by providing higher bead zone width compared to same in the specified rim drawing.

Vertical compression was achieved by reducing the ID of tyre compared to rim ID.

Both settings can influence tyre width and tyre OD to a very small extent but this was taken care of by selecting these norms to fall in line with the requirement of ETRTO (European) specifications.


All the solid cushioned tyres produced with such compression showed zero slip. A strong chemical antifatigue agent used in the bead zone formulation ensured that development of fatigue was considerably reduced to avoid fatigue failures even after substantial ageing.

EU DIRECTIVE RELATED TO VIBRATIONS

Amongst several world standards one specific directive that covers this subject is Directive 2002 / 44 / Ec of the European Parliament and of the Council of the European Union (25 June 2002). This directive covers minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibrations). Though this is directed to basically European community for safety, Hygiene and Health at work places, the requirements were studied and measures taken by Solidite certainly helped to reduce risks due to vibrations and shocks. Solid cushioned tyres produced by Solidite thus satisfy basic requirements of this directive.

This specifically satisfies the point 3 of the directive which says that it is necessary to introduce measures protecting workers from the risk arising from vibrations. Use of Solidite solid tyres can thus contribute to a great extent to minimize vibration effect.

It will not be out of place here to mention that several Indian companies are also signatories to worldwide authorities like Global Reporting Initiatives (GRI) which shows India’s awareness and commitment to Global requirements.

WET SKID RESISTANCE
(REFERENCE POINT 7, EU DIRECTIVE 2005 / 69 / EC)

Extensive work has been carried out by several tyre technologists on Wet-Skid resistance and while techniques are being developed to measure ‘skid’ and attempts made to correlate effects with likely causes, the subject of skid resistance has still remained highly complex.

Rather than chasing, the quantitative regression equations to arrive at skid resistance mathematically it is more logical to consider observations and to arrive at guide information that may help tyre technologists in designing tyres to have best possible skid resistance. With this view in mind following observations have been considered in suggesting practical ways to handle skid.

  • Wet slippery roads, contamination with debris such as general slush or mud, high speeds in cornering, defective braking system and above all bad old tyres are the frequent causes of skidding. Even the knowledge of this by a trucker in a country like India is as important as scientific aspects of this subject.
  • High resilience is an important factor that contributes towards skid, (Particularly wet skid resistance which is poor with polybutadiene). A compound of polybutadiene having some 20% higher rebound compared to its blend with natural rubber will certainly have skid resistance as indicated by stopping distance lower by at least 10%. Addition of SBR or substitution by EPDM will therefore improve wet skid resistance. It is also possible to reduce rebound by means of compounding.
  • Hardness contribution towards wet skid is also well acknowledged. Following data reveals this clearly.
    Rubber
    Hardness
    Stopping distance (ft observed)
    BR
    62
    180
    NR / BR
    57
    163
    SBR / BR
    55
    158
    SBR
    52
    151
  • Loss of fine particles due to abrasion is also a contributing factor towards skid. Brittleness in a polymer therefore can be a serious cause of skidding tendency of a tyre. Stiffening of a polymer to a brittle state is associated with glass transition temperature and hence a polymer with TG closer to operating temperatures will be most dangerous as it will have a high potential of causing low temperature stiffness. With polymer having TG between 30 degree centigrade to 105 degree centigrade, wet skid resistance is known to inversely dependant on TG. With polymers that are available in India the order of merit can be established as under (sign > stands to indicate superior wet skid resistance) as far as wet skid resistance is concerned.

Solidite tyres use, polymers chosen from a range where TG is not higher than –40 degree centigrade. Even though temperatures like –40 degree centigrade are not experienced in India often, the low temperature stiffening component continues to be present to an extent in polymers even above their TG. TG of required level can be obtained by blending those polymers in required ratio.

RESTRICTION (LEADING TO ELIMINATION) OF AROMATIC OILS

EU Directive 2005 / 69 / Ec has pointed out that materials like Aromatic oils used in oil extended rubbers and in compounding of rubber contain dangerous elements like Polycylic Aromatic Hydrocarbons presence of PAHS makes the extender aromatic oil suspects to be carcinogenic, mutagenic and toxic to reproduction.

The said Directive, though is restricted its application to only four selected sizes of Pneumatic tyres, Solidite undertook the required R&D work to replace the aromatic oil from basic polymers and in processing.

In USA, the OSHA (Occupational Safety and Health Administration) adopted the IARC (International Agency for Research on Cancer) report which classified untreated Naphtenic oils as carcinogenic and a user of such oils has to have a statement on the Material Safety Data Sheet (MSDS) that it contains untreated naphthenic oil which is considered carcinogenic. This is also applicable to oils which contain Polynuclear Aromatics (PNA).

ELIMINATION OF OIL EXTENDED RUBBER

Only common OE synthetic rubber used was SBR 1712 which contains 37.5 PHR of highly aromatic oil. Basic norms without its usage can be seen below. This was considered as a
basic change formula and other requirements were adjusted by selective use of fillers and other compounding materials. Basic comparison of SBR 1712 with our NR compound given below is good enough to understand the change. Actual component formulations cannot be disclosed for obvious reasons.

SBR 1712
Natural Rubber
A
B
Rubber
137.50
100.00
100.00
Zinc oxide
5.00
5.00
5.00
Stearic Acid
2.00
2.00
2.00
Non Aromatic / Non Mineral
oil (Process oil 500)
-
15.00
15.00
Carbon Black (HAF)
50.00
50.00
45.00
PPT Silica
-
Not disclosed
Not disclosed
Diethylene Glycol
-
1.00
1.00
CBS
1.20
1.00
1.00
TMT
0.20
0.15
0.15
Antioxidant
1.00
1.00
1.00
Sulphur
2.00
2.20
2.50

Properties

SBR 1712
Natural Rubber
A
B
ML 4 @ 100 deg. C
45.0
48.0
45.0
Rheometric MI
31.0
36.0
33.0
Rheometric ML
22.0
26.0
23.0
Thermoplasticity
9.0
10.0
10.0
Scorch – t2 (150 degree centigrade)
2.5
2.4
2.4
Optimum cure t90 (150 degree centigrade)
8.9
8.8
8.8

Cured at 150 deg. C for 30 minutes

SBR 1712
Natural Rubber
A
B
Tensile strength psi
Kg / cm2
3250
3300
3400
232.1
235.70
243.0
300% Modulus psi
Kg / cm2
1240
1260
1250
88.6
90.0
89.0
Elongation %
Hardness Shore A
550
580
570
54
57
55
Abrasion Index
120
122
122

Basically the concerned EU directive is applicable to only a selected range of Pneumatic tyres probably due to reference to wet skid resistance. Nevertheless, even solid tyres use aromatic oils as processing aids and Solidite took quick steps to replace these oils with suitable ones (that do not have suspected polycyclic aromatic hydrocarbon).

PROCESS OILS IN COMPOUNDING

EU Directive 2005 / 69 / EC points out that not only the oil extended rubbers contain such extender oils that carry Polycyclic Aromatic Hydrocarbons that are not added intentionally but when such oils are used as a processing aid in rubber compounds they automatically find way to be present in the tyres and other products also.

Completed in 2008,Solidite successfully implemented a programme to totally replace Naphthanic and Aromatic oils

NON-MARKING TYRES

Sulphur donors and antioxidants have to be within the limits cleared by FDA(section 121.2562 of the code of Federal Regulations) for rubber articles that come in repeated or continuous contact with food products.

Solidite tread and sidewall compounds of non–marking solid cushioned tyres are designed to observe the required limits stipulated by FDA.

While every effort has been made to see that data provided in this technical note is accurate; the company Solidite Rubber Industries Pvt. Ltd or the authors are in no way responsible for results of the application of this data as conditions of applications are beyond the control of the company or the authors.

Comments are closed.