Chicago 2002 Paper

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New Additive Solutions for the PVC Industry

CONFERENCE PAPER · SEPTEMBER 2002

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3 AUTHORS, INCLUDING:

Wolfgang Andreas Voigt

Lonza

10 PUBLICATIONS 19 CITATIONS

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Available from: Wolfgang Andreas Voigt

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New Additive Solutions for the PVC Industry

Alex Wegmann, Alfred G. Oertli, Wolfgang Voigt

Ciba Specialty Chemicals Inc.

Plastic Additives Segment

CH-4002 Basel / Switzerland

Abstract

Phenolic products, especially sterically hindered phenols, are widely used throughout the PVC industry.

For instance, as chain-stoppers and antioxidants in PVC polymerization, to terminate the reaction and

prevent degradation of the virgin resin in the stripper and dryer. Methylmethacrylate-butadiene-styrene

(MBS), a frequently used impact modifier for rigid PVC, needs highly efficient protection against

oxidative degradation of its rubber phase by a synergistic blend of a phenolic antioxidant with a

thiosynergist. Plasticizers for flexible PVC in thermally demanding applications are also stabilized with

phenolic antioxidants.

In the above mentioned applications, traditionally used solid antioxidants are increasingly replaced by

more efficient, liquid products which give additional invaluable advantages in handling, dosing, and ease

of emulsification, very important for introduction into aqueous processes, as well as a good toxicological

profile, enabling broad registration and food approval status, thereby enhancing PVC's environmental

acceptance. Alternatively to stabilizing plasticizers, or to further boost the thermal stability of PVC, solidhindered phenol antioxidants can be added to heat stabilizers, or directly to the compound.

Newly developed high performance light stabilizers and other effect additives (biocides, antistats,

antifogging and fluorescent whitening agents, etc.) enhance the quality of finished PVC articles, thereby

further strengthening the position of PVC applications in the marketplace.

1) Introduction:

PVC is one the most important thermoplastic polymers, approximately 25 million tons are produced and

processed each year. PVC is very versatile, and can be mixed with a variety of other polymers orsubstances, to modify its mechanical and physical properties, very important among them are impact

modifiers for rigid PVC (e.g., MBS, acrylates), plasticizers for flexible PVC (e.g., phthalates, adipates,

trimellitates), pigments, fillers, thermal stabilizers (salts based on Pb, Ca/Zn, Sn, etc.), effect additives

(UV light stabilizers, biocides, antistats, antifogging and fluorescent whitening agents, etc.). Hindered

phenols are used in the polymerization of PVC, of MBS resins, and also for the stabilization of

plasticizers, thermal stabilizers, and PVC compounds (figure 1).

2) Chain-stopper / antioxidant for the PVC polymerization process [1]:


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A good chain-terminator has to stop the polymerization reaction completely, and quench any remaining

catalyst residues (radicals), to avoid post-polymerization during the work-up of the resin. This will

guarantee less cleaning operations and, thus, a better plant productivity. IRGANOX® 1141 (AO1) is a

synergistic liquid blend of two hindered phenols (figure 2). It is an excellent chain-stopper and catalyst

quencher, and its antioxidant properties give good thermal stability to PVC resins and compounds.

Moreover, the liquid supply form ensures easy handling, storing, and dosing. There are no dust

problems, nor organic solvents or carriers needed. This greatly reduces potential health, fire and

environmental hazards. The product can be added to the aqueous PVC suspension, either as straight

liquid, or, alternatively, as emulsion. The low viscosity makes it easy to emulsify. There is no significant

weight loss of AO1 in the temperature range relevant to the PVC polymerization, stripping, and drying,

i.e. up to 150°C. AO1 is increasingly replacing traditionally used products such as BPA (Bisphenol A)

or BHT (di-t-Butyl-Hydroxy-Toluene).

3) Polymerization of MBS:

MBS is produced, similarly to ABS, by emulsion copolymerisation of a rubber (polybutadiene or

styrene-butadiene-rubber) together with styrene and methylmethacrylate. The MBS copolymer is

separated from water by coagulation, centrifugation and drying. MBS has a large internal surface area

(because its particles are very small) and contains a high amount of unsaturated rubber (up to

approximately 80%). Therefore, it is very prone to oxidation in the drying step in presence of oxygen,

and needs extremely efficient thermal protection. Market requirements for antioxidants for MBS: give

very good thermal stability to the MBS powder, as well as better heat stability to PVC compounds

modified with MBS, improved handling of the additive, better cost/performance, easier preparation and

better storage stability of antioxidant emulsions.

State of the art have been solid, fully or partially hindered phenols, like IRGANOX® 1076 (OBP) or

IRGANOX® 245 (AO2) in emulsified form, together with thiosynergists, like DLTDP (dilauryl-

thiodipropionate) or DSTDP (distearyl-thiodipropionate). Here also, the liquid supply form of AO1 is a

big advantage. It can be emulsified easily, and the emulsion can be stored at room temperature. Figure 3

shows that AO1 is even better in thermal stabilization than other hindered phenols, and it also improves

the performance of PVC in the milling test (figure 4).

4) Antioxidants for plasticizers:

Only for thermally very demanding applications, like flexible PVC for wire & cable or automotiveinterior, plasticizers need to be stabilized with antioxidants. The main purpose of the antioxidant is to

protect the plasticizer in the PVC formulation against thermal oxidation during the processing, as well as

during the manufacturing and the life time of the finished article. In presence of oxygen, tertiary carbon

atoms in the plasticizer can undergo autoxidation to form, ultimately, low molecular weight acids that

have no more plastifying effect (figure 5). The antioxidant, in combination with traditional heat stabilizers

(e.g. salts containing Sn, Pb, Ca/Zn), also helps to protect the PVC to a certain extent against

dehydrochlorination. This is also important because hydrogen chloride released during the thermal

dehydrochlorination of PVC can further accelerate the decomposition of the plasticizer.


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Up to now, BPA has clearly dominated the market for the stabilization of plasticizers. For practical

reasons, and to ensure a homogeneous distribution, the antioxidant is usually added to the plasticizer.

Important requirements the antioxidant has to fulfill: Miscibility, compatibility, and good solubility in the

plasticizer; low volatility (little weight loss during thermal aging), and no fogging tendency; retention of

mechanical properties (tensile strength, elongation), no discoloration, and low hydrogen chloride release

under thermo-oxidative conditions.

In the so-called “Congo-Red-Test” (DIN VDE 0207 part 614), a good measure for the efficiency of an

antioxidant, IRGASTAB® PVC 11 (AO PL-L), based on very similar chemistry as AO1, shows a

similar performance as BPA or OBP, whereas BHT is clearly inferior (figure 6). The clear advantage of

AO PL-L is the liquid supply form that renders it well soluble in plasticizers, compared to solid products,

and makes its handling and dosing very easy. The weight loss in a PVC compound (14 days/ 140°C) is

approximately 5%, comparable to BPA. Alternatively, the antioxidant can be added by the PVC

compounder to the PVC formulation, in this case a solid supply form is preferred. IRGASTAB® PVC

86 (AO CO-S) fulfills this requirement, and is also very effective in the Congo-Red-Test.

5) Regulatory issues:

Lately, BPA has come under pressure because of its alleged endocrine modulating properties (“estrogen

mimic”). Therefore, the PVC industry in Western Europe has made the decision to phase-out BPA in

PVC polymerization by the end of 2001. Depending on the actual recipes, the amount of BPA in PVC

compound formulations, needed for the stabilization of plasticizers, is about 10x higher than the amount

from the polymerization step. Therefore, the phase-out of BPA in PVC resins will remain of limited

practical value, as far as the concentration of BPA in the final PVC article is concerned, as long as BPA

is still used in plasticizers. Nevertheless, it is a first step and clear signal that the PVC industry isdetermined to use additives which strengthen the image of PVC from an environmental point of view,

and foster it’s sustainable future.

Investigations have shown that AO1, and also AO PL-L and AO CO-S, do not show endocrine

modulating properties. Besides, the products have very favorable toxicological profiles, and are

registered globally. They have FDA approval for rigid PVC (0.04%), as well as for flexible PVC

(0.03%), in PVC films thinner than 1 mil (= 2.5mm), for aqueous and acidic food. In Europe, the

components of AO1 are approved in all plastics up to a SML (specific migration limit) of 1mg/kg food

(CGX AO 145), respectively 6 mg/kg food (OBP).

6) Effect additives:

High Performance UV Light Stabilizers

PVC compounds have traditionally been stabilized by hydroxyphenyl-benzophenone or hydroxyphenyl-

benzotriazole UV-absorbers (UVA). Although in certain formulations Hindered Amine Light Stabilizers

(HALS) showed an improvement of the light stability, HALS have so far not found broad acceptance in

PVC light stabilization. The reason is, most likely, that hydrogen chloride released during degradation of

PVC can protonate the HALS, thereby reducing their efficacy. Now, new high performance UV light

stabilizer systems (TINUVIN® XT) have been developed, that can be effectively tailored towards the


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type of PVC compound and its application. They do not react easily with hydrogen chloride, showing a

considerably improved light stability after artificial weathering, in retention of color (figure 7) and

mechanical properties (table 1).

Biocides

IRGAGUARD® A 2000 (white powder, melting range 128 - 133°C) prevents the growth of algae, moss,

etc., on the surface of PVC articles (inliners, sidings, roofings, tents, etc.), thereby retaining the or iginal

appearance and transparency. Due to the good compatibility with PVC, it is highly efficient. Controlled

release of the molecule ensures an excellent long-term activity. It is highly specific and effective, by

inhibiting the photosynthesis in the algae (figure 8). The product has favorable toxicity and ecotoxicity

profiles: low acute toxicity, not irritant, not mutagenic, only weakly skin sensitizing, and inherently

biodegradable. Despite the intended high toxicity against algae, the product is not toxic against

invertebrates, birds, fish, and sediment living organisms.

IRGAGUARD® B 1000, a bacteriostatic antimicrobial, can be incorporated into polymers, often via a

masterbatch. It migrates to the surface of the finished articles, thus inhibiting the growth of many

microorganisms (bacteria, mold, yeast, etc.) and, thereby, considerably increasing safety, hygiene, and

health standards. This antimicrobial is supplied as a fine, thermally stable (>300°C) powder, with a

melting point of 57°C. It is highly effective, has a broad spectrum of activity, and does not cause

resistance in microorganisms. Whereas PVC itself is relatively resistant to microbial attack, plasticizers,

fillers, pigments, and additives in the plastic can serve microorganisms as nutrients. Figure 9

demonstrates visually the efficacy of the antimicrobial in a rigid PVC formulation: there is a large zone

free of microbes around the treated article.

Antistatic Additives

Static electricity is commonly generated in polymers by friction. High electrical charges can have a

negative impact on polymer production and processing (risk of electrical shocks to employees, risk of

spontaneous electrical discharges causing fires or explosions, etc.), as well as on the use and appearance

of finished plastic materials (e.g., dust contamination). The magnitude of the charge depends on the

degree of contact, the plastic’s frictional and intrinsical electrical properties (dielectric constant and

resistivity), as well as the surrounding medium (relative humidity).

Antistatic additives are amphiphilic molecules, capable of reducing electrical charges on plastic surfaces

by rendering them slightly conductive, i.e. lowering their surface resistivity. Surface resistivity is defined

as the intensity of current flowing over the surface of a plastic when a given potential is applied between

two electrodes (ASTM D257). Internal antistats are added to polymers during the processing. In the

finished article they continuously migrate to the surface, where they adsorb water in order to develop a

mid to long term effect of reduced resistivity (figure 10). The rate of migration is influenced by the

concentration of the antistat, the temperature, the relative compatibility of the antistat with the polymer,

the polymer crystallinity (migration proceeds through the amorphous phase), and potential co-additives.

Fillers and pigments tend to adsorb and retard migration, whereas HALS and slip additives tend to

promote it. For good antistatic properties, the surface resistivity should be lower than 10-12 Ohm/Square.


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ATMER 190 (AS-1, based on alkyl sulphonate) provides the best performance in terms of lowering

surface resistivity in rigid PVC. It is very suitable for high temperature processing, but leads to opacity in

clear articles. ATMER 129 (AS-2, based on GMS = glycerolmonostearate), on the other hand, is less

efficient, but has no adverse effect on transparency (figure 11). In flexible PVC, ATMER 154 (AS-3,

based on ethoxylated coconut acid) performs better than AS-2 (figure 12). An additional advantage of

AS-3 is its liquid product form, which enables an easy miscibility with other components in the PVC

formulation. In general, AS-2 is a suitable short term antistat with a quick performance build-up, but

provides less long-term effect compared to AS-3.

Antifogging Additives

The term “fogging” is typically used to describe the condensation of water vapor upon a plastic film’s

surface in form of small discrete droplets. Fogging may be observed when an enclosed mass of humid air

cools to a temperature below its dew point. This effect is especially undesired in food packages, stored

in refrigerated cabinets, where condensed water droplets reduce the attractiveness of the packed good,

and in agricultural applications, such as greenhouses, where the droplets and the resulting loss of

transparency reduces the light transmission and, therefore, the crop growth behind the film. Antifogging

Agents reduce the surface tension of the film, are soluble in water and, thus, lead to an improved spread-

out of the water on the surface. The desired lifetime of the antifog effect necessitates a clear distinction

between the two major applications: food packaging and agricultural films:

In food packaging, the antifog effect should typically last for a few days, as the packed good will

normally not exceed a shelf life longer than one week in the cold cabinet. An excellent reduction of fog

formation in PVC with classical plasticizers is achieved by a combination of an ethoxylated sorbitan ester

such as ATMER 116 (AF-1) with a glycerol ester such as ATMER 1010 (AF-2) in a ratio of 1:2 or1: 3 (table 2). If polymeric plasticizers are used, the migration of the antifogging agent is often reduced.

In these cases, the use of a sorbitan ester, e.g. ATMER 100 (AF-3) should be taken into

consideration. The choice of a suitable greenhouse antifogging agent is governed by different

requirements: long term performance for several months or years and continuous wash-off of the

antifogging agent by the condensed water necessitate a different approach: PVC films for greenhouse

application with “antifogging effect” typically contain sorbitan esters such as ATMER 103 (AF-4) with

a modified chemical structure in order to maximize the duration of the effect and to minimize the

extractability of the surfactant.

Fluorescent Whitening Agents (FWA):

Many thermoplastics absorb light in the blue spectral range of natural daylight (“blue defect”), hence

causing a more or less pronounced yellowish appearance. Fluorescent whitening agents, or optical

brighteners, are capable of absorbing invisible UV radiation, converting it to longer wavelength and re-

emitting it as a visible blue or violet light (fluorescence). Thereby, the unwanted yellowish appearance of

the substrate is compensated and, in addition, more visible light in the range of 400 to 600 nm is

reflected than was originally incident; hence the article appears whiter, brighter and more brilliant (figure

13). In practice, concentrations of 50 - 500 ppm of fluorescent whitening agents are used in

thermoplastics. Benefits for the end use articles include masking of the initial color of plastics, increase of


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the brilliancy of white, black, or colored articles (fashion goods of imitation leather, packaging materials,

etc.).

For PVC, the following products are used: UVITEX® OB (FWA-1), UVITEX® FP (FWA-2);

UVITEX® OB-ONE (FWA-3). They achieve a substantial whitening effect in rigid (figure 14), and

flexible PVC (figure 15), relatively good light fastness, excellent compatibility and thermal stability, which

makes them suitable for melt processing.

7) Conclusions:

Hindered phenol antioxidants are widely used in the PVC industry as chain-stoppers and antioxidants in

PVC polymerization, thermal stabilizers for MBS impact modifiers, antioxidants for PVC plasticizers and

heat stabilizers, as well as PVC compounds. Benefits are the excellent technical performance, easy

handling (liquid supply forms), good toxicological profile, and broad food approvals. New high performance

additives for PVC compounds feature UV light stabilizers, biocides, antistats, antifogging and fluorescent

whitening agents. These additives help considerably to strengthen the performance and acceptance ofPVC in the market.

8) Bibliography:

[1] A. Wegmann, P. Xanthopoulos, Proceedings of the “Current Trends in PVC Technology

Conference”; 2000, Loughborough University, Loughborough, UK.

Figure 1: Use of phenolic antioxidants (AO) in PVC Applications

PVC Compound

PVC Resin Plasticizer forflexible PVC:

- phthalates,

- trimellitates,

- adipates, ...

Heat stabilizers

Ba / CaZn / Sn salts

pigments

Additives:

- Biocides

- Fluorescent Whitening

- Light stabilizers

- Antistats, Antifog

Impact modifier

for rigid PVC

- acrylic resin

- MBS

AO

AO

AO

AO

AO

fillers


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O H

B H T

O HOH

B P A

®IRGANOX 1076 (OBP)

OH

O

O

H3 7C18

O H

C14H 29

OH

O

O

CGX-AO1 4 5 (8 0 % ) IRGANOX® 1 0 7 6 (2 0 % )

® I R GA N OX 1 1 4 1 A O 1

H3 7C18

2I R GA N OX 2 4 5 A O 2

OH

O

O

O

Figure 2: Chemical structures of chain stoppers / antioxidants


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Figure 3: Thermal stability of MBS (DSC isothermal method, at 180°C, oxygen)

Figure 4: Thermal stability of PVC, evaluated by milling test at 180°C

Figure 5: Autoxidation mechanism of branched plasticizers

0

20

40

60

80

100

0.15% AO 1 / 0.45%

DLTDP

0.15% AO 2 / 0.45%

DLTDP

0.15% OBP / 0.45%

DLTDP

m i n u

t e s

t o t h e

m a x o

f t h e e x o

t h e r m

P V C s t a b i l i t y

M i l l i ng t es t of R -P V C c o n t a i n i n g 1 5 % M B S

0

5

1 0

1 5

2 0

2 5

3 0

3 5

0 1 0 2 0 3 0

M i l l i n g t i me i n m i n

Y e l l o w n e s s

I n d e x

O B P

A O 2

A O 1

M B S S t a b i l i z a t i o n :

0 . 2 % A O +

1 . 0 % D L T D P

P V C s t a b i l i z a t i o n :

o c t y l t i n s t a b i l i z e d

ŸCH2-(CH2)x-1-CH3-C-(CH2)x-CH3

OOH O2

CH2

CH3

β-scission -C

O

+

CH2

CH3

-C-(CH2)x-CH3

OŸ

CH2

CH3

R-C-(CH2)x-CH3

CH2

CH3

ACIDS

O2 / HŸ

HOO-CH2-(CH2)x-1-CH3 C -(CH2)x-1-CH3

H

O


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Figure 6: Performance of antioxidants in plasticized cable formulations

Figure 7: Color retention of flexible PVC after artificial weathering

Table 1: Retention of mechanical properties of flexible PVC after artificial weathering

74

95.5

136125

132 130

0

40

80

120

160

C o n g o - R e d - V a l u e

( m i n u

t e s )

c o n t r o l B H

T B P

A O B P

A O P L - L

A O C O -

S

PVC Sheathing

Formulation: parts

PVC 100.0DIDP 52.0

Filler 50.0

Heat stabilizer 4.5

AO 0.3

Lab Test: Congored

DIN VDE 0207 part 614)

-1

0

1

2

3

4

5

6

0 2000 4000 6000 8000 10000 12000

Hours

D e l t a Y I

0.5 parts Benzophenone UVA

0.5 parts High Performance UV LS3.0 parts Ba/Zn

Thermal stabilizer

0.5 mm plaques;

WOM (xenon)ASTM G 26

% Retention of elongation

after artificial weathering

2000 Hrs 4000 Hrs 6000 Hrs 8000 Hrs

0.5% Benzophenone UVA 100 100 100 71

0.5% High Performance

UV Light Stabilizer

100 100 100 91


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Control 0.1% Algae growth inhibitor

Figure 8: Biocides for algae growth inhibition in flexible PVC

Pseudokirchneriella subcapitata SAG No. 61.81 (= Selenastrum capricornutum ATCC 22662)

Incubation period 7 days at 25°C, continuous light 100 Microeinstein / m2 x sec (400-700 nm)

(1 Einstein = 1 Mol Photons = 6 x 1023 photons)].

No Microbial 0.1% Microbial 0.5% Microbial

Growth Inhibitor Growth Inhibitor Growth Inhibitor

Figure 9: Microbial Growth Inhibitors in rigid PVC formulations

(Staphylococcus aureus ATCC 9144)

H2O

H2OH2O

H2OH2O H2OH2O

H2O

H2OH2O

H2O

H2OH2O

H2OH2O H2OH2O

Plastic part

Amphiphilic

Antistatic

Agent


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Figure 10: Mode of action of antistatic agents


13/17


14/17


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Table 2: Antifogging agents in flexible PVC food wrap films

Figure 13: Mode of action of fluorescent whitening agents

Untreated material:

absorbs only visible, mainly blue

light à yellow cast

Material + FWA: UV also absorbed,

converted to blue light à reflectance

+ fluorescence. Compensates yellow cast

and increases brilliance

incident

radiation

reflection

visible light

absorption

UV light

absorption

Description Performance Rating

Opaque layer of small fog droplets Very poor A

Opaque or transparent layer of large droplets Poor B

Complete layer of large transparent drops Poor C

Randomly scattered or large transparent drops Good D

Trans arent film dis la in no visible water Excellent E

time 5

M

30

M

1

HR

3

HR

6

HR

1

D

4

D

1

W

control A A A AB AB AB AB AB

3 parts

AF-2

DE DE E E E E E E

cold fog test

refrigerator 4°C

water

film


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Figure 14: Whiteness index of a rigid PVC formulation as function of FWA concentration

Figure 15: Whiteness index of a flexible PVC formulation as function of

FWA concentration

50

70

90

110

130

150

170

0 200 400 600 800 1000

concentration [ppm]

W h i t e n e s s I n d e x

( G A N Z )

Control FWA- 1

FWA- 2 FWA- 3

Rigid PVC

Formulation:

parts

100.0 PVC

2.5 S/Sn stabilizer

2.0 ESBO

0.2 Lubricants

5.0 Titanium dioxide

compression molded

50

70

90

110

130

150

170

190

210

0 200 400 600 800 1000

concentration [ppm]

W h i t e n e s s

I n d e x

( G A N Z )

Control FWA- 1

FWA- 2 FWA- 3

Flexible PVC

Formulation:

parts

100.0 PVC

35.0 DOP

2.0 Thermal-

stabilizer

5.0 Titanium

dioxide

compression molded


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Chicago 2002 Paper