EoW March 2009

EuroWire – March 2009

technical article

The most common small-scale test method

for measuring smoke from burning

products is the traditional NBS smoke

chamber in the vertical mode, according

ASTM E662. Because of the great number

of possible parameters that influence

burning and smoke propagation, a real fire

scenario cannot be simulated in the NBS

chamber. However, it is possible to assess

smoke generation of various formulations

under identical boundary conditions.

The ASTM standard requires measurements

in both the non-flaming mode (where the

sample, mounted in a vertical position, is

subjected only to a heat radiant source)

and the flaming mode (with flaming to the

bottom of the sample).

The resulting smoke reduces the intensity

of a light beam that vertically crosses the

chamber.

Toxicity

Finally, fire hazard also is

associated, at least to some extent, with

the toxicity of the smoke itself. The main

reason for this is that the most important

toxic product in any fire is carbon

monoxide (CO), which is produced by all

organic materials when they burn.

During combustion PVC, compared with

other materials, gives offmore hydrochloric

acid and little carbon monoxide. Both

of these gases are toxic, but with one

substantial difference.

The hydrochloric acid is immediately

perceptible and irritating, with an acrid

odour that stimulates people to leave the

affected area. Moreover, it will deposit

itself on the walls, disappearing quickly

from the gaseous mass.

Carbon monoxide, instead, is odourless

and flavourless, building up a concen-

tration enough to cause unconsciousness

before evacuation from the area has

occurred.

It is the carbon monoxide, and the heat

and the smoke that develops with the

combustion of all the organic materials

that is mainly responsible for deaths

during fires: it is called “the silent killer”.

So far as the risk of formation of dioxins

is concerned (normally correlated to the

uncontrolled combustion of materials

containing chlorine), it appears from

studies that the amounts emitted during

an accidental fire are very small.

There is no noticeable increase (the levels

are lower than 0.1%) of the general level of

dioxins present in the atmosphere.

There are therefore no increased risks to

people or the atmosphere in the case of a

fire that involves large amounts of PVC.

2 PVC compounds:

a contribution to

sustainability

The trend of the last years is to eliminate

risks to the environment and to human

health.

The RoHS (directive 2002/95 EC) stands

for ‘the restriction of the use of certain

hazardous substances in electrical and

electronic equipment.’ This directive

bans the placing on the EU market of

new electrical and electronic equipment

containing more than agreed levels of

lead, cadmium, mercury, hexavalent

chromium, polybrominated biphenyl (PBB)

and polybrominated diphenyl ether (PBDE)

flame retardants. This is only one of the

steps in order to arrive at the production of

materials that respect the environment.

On 1

June 2007, Regulation EC 1907/2006

REACH (Registration Evaluation and

Authorisation of Chemicals) came into

force, for an elevated level of protection of

human health and the atmosphere.

It included the promotion of different

methods for the evaluation of the dangers

that the substances involve, let alone the

free circulation of substances in EU market,

strengthening at the same time the

competitiveness and the innovation.

The Reach priorities are:

registration of about 30,000 substances,

•

commercialised before 1981 and

produced or imported in amounts of

1 ton a year; defining principle OSOR

‘one substance, one registration’ and

to invert the burden of proof to make

the people who place chemicals on the

market (manufacturers and importers)

responsible for understanding and

managing the risks associated with

their use

authorisation and substitution of the

•

dangerous substances, assuring that

the risks are adequately controlled

and that these substances are replaced

by suitable substances or alternative

technologies

compliance by manufacturers, impor-

•

ters and users

restrictions in specific applications

•

to provide a high level of protection

•

of human health and the environment

from the use of chemicals

availability of relevant data (no data –

•

no market)

Due to its versatility in applications and its

cost competitiveness, PVC has remained

a material of choice for the construction

industry as well as for medical parts

and equipment since its large-scale

introduction in the early 1950s.

Resin manufacturing and the nature of

stabilisers have undergone a tremendous

change during the past decade as a result

of regulatory limitations of hazardous

substances, as well as efforts to make the

material recyclable and complying with

sustainability requirements.

PVC stabilisers have long been under scru-

tiny and there is much concern regarding

heavy metal-containing products.

As a result, many restrictions are being

imposed, either by the industry itself,

by governmental regulations or by PVC

users. An example of this versatility is the

replacement of lead stabilisers with other

heavy metal-free systems as Ba-Zn, Ca-Zn

and Al/Mg/Ca/Zn stabilisers.

3 Targets for

development of FREC

(Flame Retardant Eco

Compounds)

The B & B Compounds project was

targeted at developing a new range of

PVC flame retardant eco-compounds.

There are a number of technological

options available to replace heavy metal

stabilisers and Sb

3.1 The function of stabilisers in PVC

When PVC is processed at high

temperatures, it is degraded by de-

hydrochlorination, chain scission, and

crosslinking of macromolecules. Free

hydrogen chloride (HCl) evolves and

discolouration of the resin occurs along

with important changes in physical and

chemical properties. The evolution of

HCl takes place by elimination from the

polymer backbone; discolouration results

from the formation of conjugated polyene

sequences of 5 to 30 double bonds

(primary reactions).

Subsequent reactions of highly reactive

conjugated polyenes crosslink or cleave

the polymer chain, and form benzene and

condensed and/or alkalised benzenes in

trace amounts depending on tempera-

ture and available oxygen (secondary

reactions).

Degradation must be controlled by the

addition of stabilisers. The heat stabiliser

must prevent the de-hydrochlorination

reaction that is the primary process in

degradation.

Chain reaction

(zip mechanism)

HCI

PVC

HCI