**2. Properties of Flexidones in soft-PVC applications**

In terms of worldwide consumption polyvinyl chloride (PVC) stands in third place behind polyethylene (PE) and polypropylene (PP). Thank to the development of a wide range of functional additives, in particular thank to effective plasticizers PVC could achieve this important commercial relevance. PVC is one of the few thermoplastics whose hardness can be adjusted from rubber-like elasticity up to hard formulations (Franck & Knoblauch, 2005). Thus for well over 50 years plasticizers have been playing a significant role in the manufacture of soft PVC products for the most versatile applications from floor coverings to roof membranes, cable insulation to blood bags.

With a market share of approximately 85 % phthalate plasticizers — di-2-ethyl hexyl phthalate (DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP) represent the most significant class of plasticizers at present. They are the all-rounders amongst plasticizers. The remaining 15 % are taken up by plasticizers that show excellent properties in particular areas even if they have weaknesses in others. For instance trimellittic acid esters exhibit particularly good heat stability, whilst phosphoric acid esters confer re resistance. Polymeric plasticizers (polyesters) come into play when excellent oil resistance and very good migration behaviour is required.

However, for more than 25 years, plasticizers in particular phthalates, have been the subject of environmental and health debate despite attempts by the industry to defend their current status with ever new data. This has however initiated the development of numerous new plasticizers as phthalate substitutes with less toxicological concern. One of the best known examples of these new plasticizers is Hexamoll DINCH (1.2-cyclohexanedicarboxylic acid diisononyl ester) which was developed by BASF for sensitive applications.

Unfortunately most of the newly developed plasticizer alternatives do hardly offer any improvements in the processing behaviour or property prole of soft PVC alongside the ecological or toxicological factors.

Now, however, ISP-Ashland Specialty Ingredients, Cologne, Germany, and the Institute for Materials Technology at the University of Applied Sciences Cologne (Institut für Werkstoffanwendung der Fachhochschule Köln) have collaborated to develop a new class of plasticizers for PVC based on linear alkyl pyrrolidones. Initial results show that they are not only free from physiological concerns – e.g. acute toxicity is relatively low, dependent on alkyl chain length so that the LD5O for example lies between 2.05 g/kg for Flexidone 100 (C-8 Pyrrolidone) and >12 g/kg for Flexidone 500 (C-16/18 Pyrrolidone) (Ansell & Fowler, 1988) –, but also possess several outstanding properties. These properties enable gentler, cost saving processing of soft PVC and make it possible to produce highly exible products for low temperature applications.

#### **2.1 Structure and mode of action**

Due to the planar structure of pyrrolidones the oxygen with its high electronegativity can easily cause an electron to delocalize (Fig. 1). This produces a strong dipole moment.

the products are now industrially produced REACH-compliant types that are globally

In terms of worldwide consumption polyvinyl chloride (PVC) stands in third place behind polyethylene (PE) and polypropylene (PP). Thank to the development of a wide range of functional additives, in particular thank to effective plasticizers PVC could achieve this important commercial relevance. PVC is one of the few thermoplastics whose hardness can be adjusted from rubber-like elasticity up to hard formulations (Franck & Knoblauch, 2005). Thus for well over 50 years plasticizers have been playing a significant role in the manufacture of soft PVC products for the most versatile applications from floor coverings to

With a market share of approximately 85 % phthalate plasticizers — di-2-ethyl hexyl phthalate (DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP) represent the most significant class of plasticizers at present. They are the all-rounders amongst plasticizers. The remaining 15 % are taken up by plasticizers that show excellent properties in particular areas even if they have weaknesses in others. For instance trimellittic acid esters exhibit particularly good heat stability, whilst phosphoric acid esters confer re resistance. Polymeric plasticizers (polyesters) come into play when excellent oil resistance

However, for more than 25 years, plasticizers in particular phthalates, have been the subject of environmental and health debate despite attempts by the industry to defend their current status with ever new data. This has however initiated the development of numerous new plasticizers as phthalate substitutes with less toxicological concern. One of the best known examples of these new plasticizers is Hexamoll DINCH (1.2-cyclohexanedicarboxylic acid

Unfortunately most of the newly developed plasticizer alternatives do hardly offer any improvements in the processing behaviour or property prole of soft PVC alongside the

Now, however, ISP-Ashland Specialty Ingredients, Cologne, Germany, and the Institute for Materials Technology at the University of Applied Sciences Cologne (Institut für Werkstoffanwendung der Fachhochschule Köln) have collaborated to develop a new class of plasticizers for PVC based on linear alkyl pyrrolidones. Initial results show that they are not only free from physiological concerns – e.g. acute toxicity is relatively low, dependent on alkyl chain length so that the LD5O for example lies between 2.05 g/kg for Flexidone 100 (C-8 Pyrrolidone) and >12 g/kg for Flexidone 500 (C-16/18 Pyrrolidone) (Ansell & Fowler, 1988) –, but also possess several outstanding properties. These properties enable gentler, cost saving processing of soft PVC and make it possible to produce highly exible products

Due to the planar structure of pyrrolidones the oxygen with its high electronegativity can easily cause an electron to delocalize (Fig. 1). This produces a strong dipole moment.

diisononyl ester) which was developed by BASF for sensitive applications.

available in appropriate volumes.

**2. Properties of Flexidones in soft-PVC applications** 

roof membranes, cable insulation to blood bags.

and very good migration behaviour is required.

ecological or toxicological factors.

for low temperature applications.

**2.1 Structure and mode of action** 

Chemically binding a exible non-polar alkyl chain with a compact hydrophilic head makes the alkyl pyrrolidones soluble in both polar and non-polar solvents. Even though the alkyl chain length can be adjusted to lie between C4 and C30 it has been found that chain lengths between C8 and C18 are particularly suitable for use as plasticizers. Due to their excellent dissolving power and good compatibility with PVC both gelling temperature (very low solubility temperatures – see Fig. 2) and gelling time (see gelling curves Fig. 9 and 14) can be substantially reduced. At the same time this leads to highly flexible PVC formulations that do not lose their exibility even at extremely low temperatures.

Fig. 1. Electron delocalization in pyrrolidones.

#### **2.2 More cost effective dry blending**

A measure of the effectiveness of a plasticizer is its solubility temperature. This is the temperature at which a plasticizer completely dissolves a given PVC. Typical solubility temperatures lie between 87°C for butyl benzyl phthalate and 151°C for DINCH, with diisononyl phthalate at 129°C. Figure 2 shows the solubility temperatures for alkyl pyrrolidones with various alkyl chain lengths. It can be seen that the solubility temperature can be adjusted by chain length to lie between 52 and 80°C and is thus signicantly lower than the solubility temperatures of conventional plasticizers.

Fig. 2. The dependence of solubility temperature of various alkyl pyrrolidones on alkyl chain length in accordance with DIN 53 408.

This also reduces the time taken to produce a dry blend in a high speed cooler mixer without the need for external heating. Depending on the formulation mixing times can be reduced down to 20 % in comparison to phthalate plasticizer formulations. In addition,

Flexidone™ – A New Class of Innovative PVC Plasticizers 5

the rst available low volatility plasticizer which could facilitate cold break temperatures of

60

70

80

**K-Wert K-value** 40 Tl. DINP 60 Tl. DINP 40 Tl. Flexidone 500 60 Tl. Flexidone 500 40 Tl. Flexidone 300 60 Tl. Flexidone 300

99


Fig. 4. Determination of the low temperature break behaviour according to DIN EN 495-5 (foldability at low temperatures) for soft PVC sheets with various concentrations of Flexidone 300, Flexidone 500 and DINP for a range of PVC grades with different K-values.

Figure 5 shows the progression in Shore A hardness at temperatures between +20°C and - 50°C for Flexidone 300, Flexidone 500 and DINP as well as DOA which is a widely used low temperature plasticizer. It is very noticeable that Flexidone grades not only have a better

DINP

DOA

Flexidone 500

Flexidone 300


Fig. 5. Variation of Shore A values at temperatures between +20°C and -50°C for samples

with 60 parts of Flexidone 300, 500, DOA (dioctyl adipate) and DINP.

**Temperature [°C]**

lower than -70°C.

60

70

80

**Shore A**

90

100

processing temperatures are lowered by 20 to 40°C in comparison to classic soft PVC processing. These signicantly lower temperatures allow the use of temperature sensitive additives such as special colorants and scents and result in clear time and cost savings through the use of alkyl pyrrolidone plasticizers in comparison to standard plasticizers.

#### **2.3 Cold break at temperatures lower than -70°C**

The efficiency of the plasticizing effect of the Flexidones can be seen very clearly in comparative measurements of hardness (Shore A) in relation to the plasticizer content with DINP as the standard plasticizer (Fig. 3). These show e.g. a hardness of 80 Shore A can be achieved with 33 parts of Flexidone 300 (C-12 Pyrrolidone) compared to 60 parts of DINP. In this example the same exibility can be reached with 45 % less plasticizer.

Fig. 3. The dependence of hardness on plasticizer content (parts per100 parts of PVC) tor DINP and Flexidone 300.

The hardness is determined at room temperature, however, in many applications the temperature can be temporarily or permanently signicantly lower. Many soft PVC formulations are not only much harder at lower temperatures but also completely lose their toughness so that they are subject to brittle fracture under exural or tensile loadings. A practical test for determining this boundary temperature is DIN EN 495-5 (foldability at low temperature). However, since it is not only the plasticizer type and concentration that is responsible for low temperature behaviour, but also the molecular weight of the PVC grade used, tests were performed with two different concentrations (40 and 60 parts) of Flexidone 300, Flexidone 500 and DINP in PVC grades with K-values of 60, 70, 80 and 99 (Fig. 4). This showed that the cold break temperature could be reduced by 15 to 30°C through the use of Flexidones. At 60 parts of Flexidone 300 and 500 the exact cold break temperature could not be determined for the higher K-values since the cooling system of the tests apparatus could only produce temperatures down to -70°C and at this temperature none of the samples with each 60phr Flexidone 300 and 500 showed breakages or cracks. Flexidone 500 is therefore

processing temperatures are lowered by 20 to 40°C in comparison to classic soft PVC processing. These signicantly lower temperatures allow the use of temperature sensitive additives such as special colorants and scents and result in clear time and cost savings through the use of alkyl pyrrolidone plasticizers in comparison to standard plasticizers.

The efficiency of the plasticizing effect of the Flexidones can be seen very clearly in comparative measurements of hardness (Shore A) in relation to the plasticizer content with DINP as the standard plasticizer (Fig. 3). These show e.g. a hardness of 80 Shore A can be achieved with 33 parts of Flexidone 300 (C-12 Pyrrolidone) compared to 60 parts of DINP. In

DINP Flexidone 300

30 40 50 60 70 80

**Plasticizer content (phr)**

Fig. 3. The dependence of hardness on plasticizer content (parts per100 parts of PVC) tor

The hardness is determined at room temperature, however, in many applications the temperature can be temporarily or permanently signicantly lower. Many soft PVC formulations are not only much harder at lower temperatures but also completely lose their toughness so that they are subject to brittle fracture under exural or tensile loadings. A practical test for determining this boundary temperature is DIN EN 495-5 (foldability at low temperature). However, since it is not only the plasticizer type and concentration that is responsible for low temperature behaviour, but also the molecular weight of the PVC grade used, tests were performed with two different concentrations (40 and 60 parts) of Flexidone 300, Flexidone 500 and DINP in PVC grades with K-values of 60, 70, 80 and 99 (Fig. 4). This showed that the cold break temperature could be reduced by 15 to 30°C through the use of Flexidones. At 60 parts of Flexidone 300 and 500 the exact cold break temperature could not be determined for the higher K-values since the cooling system of the tests apparatus could only produce temperatures down to -70°C and at this temperature none of the samples with each 60phr Flexidone 300 and 500 showed breakages or cracks. Flexidone 500 is therefore

this example the same exibility can be reached with 45 % less plasticizer.

**2.3 Cold break at temperatures lower than -70°C** 

40

DINP and Flexidone 300.

50

60

70

**Shore A**

80

90

100

the rst available low volatility plasticizer which could facilitate cold break temperatures of lower than -70°C.

Fig. 4. Determination of the low temperature break behaviour according to DIN EN 495-5 (foldability at low temperatures) for soft PVC sheets with various concentrations of Flexidone 300, Flexidone 500 and DINP for a range of PVC grades with different K-values.

Figure 5 shows the progression in Shore A hardness at temperatures between +20°C and - 50°C for Flexidone 300, Flexidone 500 and DINP as well as DOA which is a widely used low temperature plasticizer. It is very noticeable that Flexidone grades not only have a better

Fig. 5. Variation of Shore A values at temperatures between +20°C and -50°C for samples with 60 parts of Flexidone 300, 500, DOA (dioctyl adipate) and DINP.

Flexidone™ – A New Class of Innovative PVC Plasticizers 7

Fig. 7. Elongation at break for soft PVC sheets with various concentrations of Flexidone 300,

Fillers are used in plasticized PVC to reduce costs, and also to facilitate a special change in properties so that the compound largely meets the requirements of the end products (Hohenberger, 2001). Among the fillers, calcium carbonate, with a worldwide market share of approximately 70%, plays the dominant role. For plasticized PVC, depending on the application (cable, floor covering, profiles, films), uncoated or coated calcium carbonate grades, with different particle sizes, can be used. For all experiments a stearic acid coated calcium carbonate with a d50% value of 2.4 µm and a top cut of 20 µm (Omya

In highly filled systems, e.g. with a calcium carbonate content of 150 phr important mechanical properties, like the tensile strength, can easily drop down to less than 50%, compared to the unfilled systems if a standard plasticizer like DINP is used. For a highly filled system with Flexidone 300 as plasticizer, all essential mechanical properties vary only insignificantly from the unfilled system. As shown in Figure 8, softness of the Flexidone 300 formulation decreases only slightly in comparison to DINP even with a filler load of 100 phr

60

80

**K-value**

Flexidone 500 and DINP in PVC of different K-values.

**2.5 Properties of highly filled systems** 

BSH) was used.

Calcium carbonate.

**Elongation at b**re**ak [%]**

plasticizing power in comparison to DINP and DOA at room temperature, but the progression in hardness with decreasing temperature is also very different, i.e. an initially even gradient is followed by a sharper rise. This means that Flexidones show signicantly higher cold exibility than conventional plasticizers at temperatures in the region of -20 °C which are typical for exterior applications. Thus the use of Flexidone grades not only enable extremely low cold break temperatures, but also delivers soft PVC with signicantly better exibility at very low temperatures.

#### **2.4 Good mechanical properties**

As Figures 6 and 7 show the mechanical properties of soft PVC lm made with Flexidone 500, particularly at higher K-values, have comparable mechanical values to samples made with the same content of DINP. This is remarkable considering that these samples are signicantly softer whilst as shown earlier also retaining their exibility down to the very low temperatures.

Fig. 6. Tensile strength of flexible PVC sheets with various concentrations of Flexidone 300, Flexidone 500 and DINP in PVC grades with different K-values.

plasticizing power in comparison to DINP and DOA at room temperature, but the progression in hardness with decreasing temperature is also very different, i.e. an initially even gradient is followed by a sharper rise. This means that Flexidones show signicantly higher cold exibility than conventional plasticizers at temperatures in the region of -20 °C which are typical for exterior applications. Thus the use of Flexidone grades not only enable extremely low cold break temperatures, but also delivers soft PVC with signicantly better

As Figures 6 and 7 show the mechanical properties of soft PVC lm made with Flexidone 500, particularly at higher K-values, have comparable mechanical values to samples made with the same content of DINP. This is remarkable considering that these samples are signicantly softer whilst as shown earlier also retaining their exibility down to the very

Fig. 6. Tensile strength of flexible PVC sheets with various concentrations of Flexidone 300,

Flexidone 500 and DINP in PVC grades with different K-values.

60

80

**K-value**

exibility at very low temperatures.

**2.4 Good mechanical properties** 

0

5

10

**Tensile strength [MPa]**

15

20

25

low temperatures.

Fig. 7. Elongation at break for soft PVC sheets with various concentrations of Flexidone 300, Flexidone 500 and DINP in PVC of different K-values.
