WO2015047077A1

WO2015047077A1 - Palm oil-based compounds as environmentally friendly plasticisers for pvc

Info

Publication number: WO2015047077A1
Application number: PCT/MY2014/000236
Authority: WO
Inventors: Seng Neon Gan; Ang Teck Chye Desmond
Original assignee: Universiti Malaya
Priority date: 2013-09-26
Filing date: 2014-09-23
Publication date: 2015-04-02
Also published as: MY171591A

Abstract

A plasticiser for polyvinyl chloride (PVC) comprising an alkyd compound derived from palm oil, a polyol and a polycarboxylic acid or acid anhydride.

Description

PALM OIL-BASED COMPOUNDS AS ENVIRONMENTALLY FRIENDLY

PLASTICISERS FOR PVC

Field of Invention

This present invention relates to a composition for plasticising polyvinyl chloride (PVC) and a method of producing thereof. In particular, the composition is substantially resistant to migration from the plasticised-PVC besides imparting flexibility therein. Background of The Invention

Polyvinyl chloride (PVC) is one of the important technical polymers that has been utilised in many industries. It can be found in wide varieties of products, ranging from structural materials and piping, medical devices, and household appliances. Raw PVC is a rigid plastic having T_g around 80-100°C as the polymer is composed of highly polar repeating units that enable strong interaction between the polymer chains. In order to improve the flexibility of the plastic, plasticisers are commonly introduced during fabrication of PVC products. Plasticisers are substances introduced into polymeric materials to modify its workability or flexibility. Despite having approximately 450 different plasticisers in the market, 90% of them are designed to plasticise PVC. Nevertheless, only 8 - 10 % of these plasticisers are considered commercially significant in terms of efficiency, stability and compatibility with PVC.

One serious problem commonly encountered is the migration of the plasticisers from the PVC matrix onto its surface, followed by leaching from the polymer. This common phenomenon is due to the fact that plasticisers are usually incorporated into the polymer through mere physical interaction with the PVC chain. These interactions are relatively weak, and the plasticisers could slowly be separated and migrate to the surface. In fact, many case studies have shown exemplified migration of plasticisers out from PVC intravenous blood bags, PVC container, plastic kitchen wrap, and plastic toys. In fact, there are some patented technologies relating to plasticisers for PVC.

An International Publication No. WO 2013/048775 Al discloses a phthalate-free plasticiser which comprises a blend of an epoxidized oil and an epoxidized fatty acid Ci to C_M ester.

A United States Patent Application Publication No. US 2012/0214920 Al reveals a bio-based plasticiser for halogen-containing polymer such as PVC. The plasticiser comprises vicinally diacylated fatty acid esters derived from vegetable oil. Apart from transesterification between diols and the vegetable oil, the synthetic route includes epoxidization of glyceride diacetate, followed by acylation with anhydrides.

Another United States Patent No. US 6797753 B2 discloses a plasticiser for PVC polymer containing fatty acids derived from vegetable oils. The fatty acids are unsaturated and fully epoxidized. Nevertheless, the disclosure is only limited to the use of vegetable oil having iodine values (I.V.) above 100.

Other prior art mentions that di-ethylhexylphthalate (DEHP) and citrate derivatives are among the commonly used plasticisers for PVC. Although introduction of plasticisers into a PVC matrix makes the polymer more flexible, some of the properties of the polymer, such as thermal stability may be compromised.

In view of the above-mentioned problems, it would be highly desirable and advantageous to develop plasticisers for PVC which possess good migration resistance. Considering the depleting and scarcity of petroleum supply, it would be even more desirable if the plasticisers are produced from sustainable materials.

Summary of The Invention

The main object of the invention is to provide a plasticiser having good migration resistance. Hence, it is safe to be used in preparation of plastic toys, food containers, plastic kitchen wrap as well as medical apparatus such as catheters.

Another object of the invention is to provide an environmentally friendly plasticiser comprising an alkyd compound derived from natural vegetable oil. Further, it provides an alternative to the use of petroleum-based plasticiser.

At least one of the preceding objects is met, in whole or in part, by the present invention, in which the embodiment of the present invention describes a plasticiser for polyvinyl chloride (PVC) comprising an alkyd compound derived from palm oil, a polyol and a polycarboxylic acid or acid anhydride.

Preferably, the palm oil is in an amount ranging from 15 to 85 wt% of the composition of the alkyd.

Preferably, the polyol is in an amount ranging from 5 to 55 wt% of the composition of the alkyd. Preferably, the polycarboxylic acid or acid anhydride is in an amount ranging from 15 to 45 wt% of the composition of the alkyd.

The polyol used is any one or more of glycerol, ethylene glycol, 1, 4-butandiol, propanediol, pentaerythritol, mannitol and sorbitol.

The polycarboxylic acid used is any one or more of maleic acid, fumaric acid, trimellitic acid, succinic acid, adipic acid and itaconic acid.

The acid anhydride is used is phthalic anhydride, maleic anhydrice or a combination thereof.

One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments described herein are not intended as limitations on the scope of the invention as well as not limited to what are described herein.

Brief Description of Drawings For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawing the preferred embodiments from an inspection of which when considered in connection with the following description, the invention, its construction and operation and many of its advantages would be readily understood and appreciated.

Figure 1 is an 1H-NMR spectrum of the disclosed plasticiser derived from palm oil with an inset of a plausible structure of the plasticiser. Figure 2 shows FTIR spectra of (a) The disclosed palm oil-base plasticiser synthesized from palm oil (b) Unplasticised PVC and (c) Plasticised- PVC. shows shifting of peaks in the expanded FTIR spectra of (a) Unplasticised PVC and Plasticised-PVC (b) The disclosed palm oil- base plasticiser and plasticised-PVC.

Figure 4 shows an experimental setup used for investigation of migration resistance in PVC plasticised using the disclosed palm oil-based plasticiser.

Figure 5 shows the FTIR spectra of (a) PVC plasticised with 20 wt of the disclosed palm oil-based plasticiser (b) PVC plasticised with 20 wt% acetyl triethyl citrate (ATEC) and (c) PVC plasticised with 20 wt% di- ethylhexylphthalate (DEHP) under migration resistance test for 1 to 8 days.

Figure 6 shows the ratio of FTIR peak absorbance (Ai₇₄₀ Ai33o) of the unplasticised PVC and plasticised-PVC which uses ATEC, DEHP and the palm oil-based plasticiser for migration resistance test.

Figure 7 shows the Differential Scanning Calorimetry (DSC) thermograms of

(a) Unplasticised PVC (b) PVC plasticised with 20 wt% of the palm oil-based plasticiser and (c) The palm oil-based plasticiser

Figure 8 shows the glass transition temperature (T_g) of PVC plasticised with the palm oil-based plasticiser at different loading based on DSC analysis and Fox relation.

Detailed Description of The Invention

The present invention relates to a plasticiser for poly(vinyl chloride) (PVC) and a method for producing thereof. In more particular, the present invention relates to an alkyd compound which is derived from palm oil through a chemical synthesizing process. The disclosed compound substantially reduces the rigidity of PVC and may serve as an alternative to petroleum-based plasticisers.

Hereinafter, the invention shall be described according to the preferred embodiments of the present invention and by referring to the accompanying description and drawings. However, it is to be understood that limiting the description to the preferred embodiments of the invention and to the drawings is merely to facilitate discussion of the present invention and it is envisioned that those skilled in the art may devise various modifications without departing from the scope of the appended claim.

The present invention discloses a plasticiser for polyvinyl chloride (PVC) comprising an alkyd compound derived from palm oil, a polyol and a polycarboxylic acid or acid anhydride. In the present invention, a composition of polymeric chains with polyfunctionality is developed to encourage strong interaction between the polymeric plasticiser with PVC chains. As a start, the present invention prefers palm oil to derive an alkyd compound. In this context, the palm oil includes palm oil derivatives such as palm stearin, palm olein, palm kernel oil or any one of the combination thereof.

The use of palm oil could reduce the overall cost of product, and yet exhibit excellent plasticizing effect. Preferably, the palm oil can be used in an amount ranging from 15 to 85 wt% of the composition of the alkyd. More preferably, 20 to 80 wt% of palm oil can be employed. In the most preferred embodiment, the present invention uses 30 to 60 wt% of palm oil.

It is important to note that the palm oil is in an amount ranging from 15 to 85 wt% of the plasticiser. The plasticiser having an amount of palm oil less than 15 wt% tend to increase in hardness and rigidity, thus has lower plasticising effect. On the other hand, the plasticiser having an amount of palm oil exceeding 85 wt% can affect workability of the plasticiser. In accordance to that, the relative amount of polycarboxylic acid or acid anhydride and polyol is reduced. Hence, the polymerization process is rendered difficult so as to obtain a polymeric plasticiser.

Preferably, the polyol is a bifunctional alcohol such as ethylene glycol, 1, 4-butandiol, or propanediol, or polyfunctional alcohol such as glycerol, pentaerythritol, mannitol or sorbitol, or any one or more thereof. Most preferably, glycerol derived from vegetable oil is used in the present invention. The alkyd is preferably prepared by reacting palm oil with glycerol to produce a predominant mixture of monoglycerides. Preferably, the reacting step involves alcoholysis of palm oil with glycerol. Notably, the alcoholysis involves the use of an alkaline catalyst. In particular, glycerol increases natural content of the resulting plasticiser. In the present invention, an amount of polyol less than 5 wt% may retard polycondensation process due to limited supply of -OH groups in the system. If the amount of polyol used is greater than 55 wt%, an excess of unreacted polyol in the product could lead to an increase in hygroscopicity of the plasticiser. Hence, the amount of the polyol used in the synthesis of the plasticiser is preferably in an amount ranging from 5 to 55 wt of the composition. More preferably, 10-35 wt% of polyol can be used. In the most preferred embodiment, 20 - 25 wt% of polyol can be utilised to produce the plasticiser. In accordance to the preceding description, the plasticiser is prepared from the reaction between the predominant mixture of monoglycerides with polycarboxylic acid or acid anhydride. Favourably, the polycarboxylic acid is any one or more of maleic acid, fumaric acid, trimellitic acid, succinic acid, adipic acid and itaconic acid. Yet, acid anhydride can also be used to react with the mixture of monoglycerides aforementioned. Preferably, the acid anhydride is phthalic anhydride, maleic anhydrice or a combination thereof. Most preferably, the phthalic anhydride is used. In the present invention, the 5- membered ring in phthalic anhydride encourage higher rate of reaction, thus reducing the overall time required to synthesize the plasticiser.

In the present invention, the amount of polycarboxylic acid or acid anhydride less than 15 wt% may retard the polycondensation process due to limited supply of - COOH groups in the system. On the other hand, an amount of polycarboxylic acid or acid anhydride greater than 45 wt% would lead to an excess of unreacted -COOH groups in the plasticiser. Hence, the amount of polycarboxylic acid or acid anhydride introduced to the mixture of monoglycerides is preferably 15 - 45 wt% of the composition. More preferably, 25 - 40 wt% can be used. Favourably, 30 - 35 wt% of polycarboxylic acid or acid anhydride is used.

In the preferred embodiment, a method of producing a plasticiser for polyvinyl chloride (PVC) comprising the steps of reacting palm oil with polyol in the presence of an alkaline catalyst at a temperature ranging from 150 to 250 °C to obtain a mixture of monoglycerides; and subjecting the mixture of monoglycerides to a polycondensation reaction with polycarboxylic acid or acid anhydride at a temperature between 200 to 240°C until the mixture achieves an acid number of 5 to 45 mg KOH g. Hence, an alkyd compound which could be used as plasticiser for PVC is essentially produced.

In the present invention, the method preferably employs palm oil including palm oil derivatives such as palm stearin, palm olein, palm kernel oil or any one or a combination thereof.

The alkaline catalyst used can be lithium hydroxide, potassium hydroxide, sodium hydroxide, calcium hydroxide, calcium carbonate or any one or combination thereof. It is important to note that the alkyd produced preferably achieves an acid number between 5-45 mg KOH/g to ensure its workability as a plasticiser. In the present invention, an acid number between 15 to 25 mg KOH/g is preferably achieved. The palm oil-based plasticiser and PVC can be blended using more than one method. A commonly practiced blending technique is dry blending, where PVC and plasticiser are mixed at elevated temperature using equipment such as heating mixer, roller mixer and cooling mixer. At temperature above the softening point of PVC, plasticiser could easily migrate into regions between the PVC chains. Consequently the glass transition temperature of the PVC would drop. Mixing at an upper limit temperature in between 140 - 170 °C is common to avoid thermal degradation of the PVC.

Solvent blending is another method that can be used to mix PVC and plasticiser. This blending is usually carried out in the presence of mutual solvent at temperature slightly higher than room temperature. After blending, the solvent is preferably removed by evaporation to obtain plasticised PVC.

Using an amount of plasticiser less than 2 wt% may not produce significant plasticizing effect, while using an amount greater than 40 wt may cause the plasticised PVC to become tacky. In the preferred embodiment, the amount of palm oil-based compound introduced into PVC is preferably 2-40 wt%, more preferably 5 - 30 wt%.

A series of evaluation tests have been conducted on the composition invented, including characterisation of the palm oil based plasticiser and plasticised PVC, shown in Figure 1 to Figure 3. Evidence of interaction between PVC and the palm oil- based plasticisers are indicated in Figure 3 which observe shifting of some characteristic peaks; the -OH peak at 3500 cm^-1 of plasticiser has shifted to 3441 cm ¹ upon blending with PVC, and peak at 2974 cm ¹ which is one of the unique peak of PVC from the stretching and deformation of C-H of -CHC1 is no longer visible in the FTIR spectrum of plasticised PVC. The peak could have shifted to a lower wave- number and merged into broad peak at 2918 cm ¹. Interaction between plasticisers and PVC is important to provide effective plasticising effect. Besides, significant interaction between plasticisers and PVC has led to excellent migration resistance of the plasticisers. Figure 4 shows the experimental setup used to investigate the migration resistance of plasticisers in the PVC. Unplasticised PVC films are used to sandwich plasticised PVC at 75 °C, and after several days, the unplasticised PVC are then removed and analyzed for trace of plasticisers on the surface of the PVC. Figure 5 shows presence of carbonyl peaks from plasticisers in the unplasticised PVC during migration resistance test. Comparison reveals that the palm oil-based plasticiser has lower migration tendency than commonly used commercial monomelic plasticisers such as di- ethylhexylphthalate (DEHP) and acetyl triethyl citrate (ATEC), as summarized in Figure 6.

The palm-oil-based plasticiser as described in the present invention reduces the glass transition temperature (T_g) of PVC, as shown in Figure 7 and 8. At high loading of plasticisers (20 wt %), T_g of the plastic has dropped from 85.3 °C to 66.7 °C.

Thermal stability of the plasticised PVC with respect to activation energy of dehydrochlorination did not significantly depreciate upon plasticisation with palm oil- based plasticiser. Based on calculation using Kissinger equation, the activation energy of dehydrochlorination of unplasticised PVC is 81.9 kJ mol ¹, whereas PVC film plasticised with 10 wt% palm oil-based compound is 76.4 kJ mol ¹, PVC plasticised with 10 wt ATEC is 69.9 kJ mol ¹ and that with 10 wt% DEHP is 72.4 kJ mol ¹. EXAMPLE

The present invention is further explained in detail based on examples, but the present invention is not limited only thereto.

(Synthesis of plasticiser)

The palm oil-based plasticiser is prepared according to the following preparation procedures. The amounts of palm oil derivative, polyol and acid anhydride are used in accordance to composition denoted in Table 1. To prepare plasticiser PI, mixture of glycerol and palm olein are heated gradually to 230 °C in the presence of Ca(OH)₂ as catalyst. The amount of Ca(OH)₂ included is 0.08 % of the weight of palm olein used. The temperature of the mixture is held at 230 °C for approximately 2 hours with constant stirring. The temperature of the mixture is then lowered to a temperature less than 150 °C, and phthalic anhydride is introduced into the reaction mixture. The temperature is then gradually increased and held around 200-240 °C until the acid number of the reaction mixture achieves approximately 20 mg KOH/g. During polycondensation, water is removed from the system using Dean-Stark trap attached to the reaction flask. Plasticiser P2 is prepared using the same experimental procedure as PI, that part of the phthalic anhydride is replaced by fumaric acid. Plasticiser P3 is prepared using the same procedure as PI, but using palm stearin instead of palm olein. Plasticiser P4 is prepared using the same procedure as P3 but part of the phthalic anhydride is replaced by maleic acid. Plasticiser P5 is also synthesized using the same procedure as plasticiser P3 but part of the phthalic anhydride is replaced by maleic anhydride during the synthesis.

Table 1 : Compositions of Plasticisers

Composition (weight )

plasticiser Palm Palm Phthalic Fumaric Maleic Maleic

Glycerol

Olein stearin anhydride acid acid anhydride

PI 45.2 - 21 .6 33.2 - -

P2 46.5 - 22.3 20.5 10.7 -

P3 - 45.2 21.6 33.2 - -

P4 - 43.2 23.7 21.8 11.4 -

P5 - 43.9 24.1 22.2 - 9.8 (Chemicals used in Example 1)

Chemicals used in the examples mentioned under Table 1 are described in the following.

Palm oil used in the examples are refined, bleached, and deodorised palm stearin (R.B.D. Palm stearin), and R.B.D. palm olein are available from Emery Oleochemical Malaysia Sendirian Berhad and they were used without further treatment. Polycarboxylic acids or acid anhydrides used in the examples include phthalic anhydride (PA obtained from Merck (Hohenbrunn, Germany), fumaric acid (FA), maleic anhydride, and maleic acid (MA) are available from Sigma Aldrich. Polyol used in the examples is glycerol 99.5 % and is available from Emery Oleo- chemical Malaysia Sendirian Berhad.

PVC used in the examples has K value 69 and is available from Sigma Aldrich. (Blending of plasticiser and PVC)

The plasticiser is dissolved in tetrahydrofuran (THF) at a concentration of 50 wt%. PVC is dissolved in THF at concentration 10 wt%. The PVC and palm oil based plasticiser solutions (in THF) are blended according to composition given in Table 2. The blending was carried out in water bath to maintain the temperature at approximately 60 °C for 6 hours. The blends are then removed and formed into films and allowed to dry through complete evaporation of the solvent.

Table 2: Compositions of PVC-plasticiser blends

Plasticised Composition / weight %

PVC PVC PI P2 P3 P4 P5

PVC-Pl-5 95 5 - -

PVC-Pl-10 90 10 - - -

PVC-Pl -15 85 15 - - -

PVC-Pl -20 80 20 - - -

PVC-P2- 10 90 - 10 - -

PVC-P3- 10 90 - 10 - -

PVC-P4-10 90 - - 10 -

PVC-P5-10 90 - - - 10

Differential scanning calorimetry (Model: Mettler Toledo 822e) was used to measure the glass transition temperature (T_g) of the plasticised PVC. The T_g of the plasticised PVC along with the T_g of the raw PVC are summarised in Table 3.

Table 3: Glass transition temperatures (T_g) of PVC-plasticiser blends

Samples T_e / °C

Raw PVC 85.3

PVC-Pl -5 76.7 PVC-Pl-10 76.0

PVC-Pl-15 68.1

PVC-Pl-20 66.0

PVC-P2-10 74.6

PVC-P3-10 76.4

PVC-P4-10 72.1

PVC-P5-10 69.4

As shown in Table 3, addition of palm oil-based plasticiser into the PVC managed to reduce the T_g of the PVC. There is a consistent reduction in the T_g with increasing amount of plasticiser PI introduced into the PVC. High amount of plasticiser in the PVC means there are more plasticisers to penetrate and occupy the region between PVC chains, and this would effectively disrupt the close proximity of the repeating units in the PVC chains. Besides, the long chains of non-polar pendant groups in the plasticiser from the fatty acids of palm oil can cause reduction in polar forces between the PVC chains. This would allow the chains to glide past each other more easily, and consequently lower the T_g of the PVC.

Plasticiser synthesized using palm stearin is having comparable plasticizing effect to plasticiser synthesized using palm olein. This can be shown by minimal difference in the T_g of PVC-Pl-10 and PVC-P3-10. Besides, using a mixture of polycarboxylic acid or acid anhydride could affect the structure of the alkyd compound produced. Consequently, the plasticising effect of the alkyd compound towards PVC may be affected. This is indicated in Table 3, where the T_g of all 5 PVC films plasticised with 10 wt% of alkyd exhibit T_g in the range of 69 - 77 °C. The present disclosure includes as contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted to without departing from the scope of the invention.

Claims

1. A plasticiser for polyvinyl chloride (PVC) comprising an alkyd compound derived from palm oil, a polyol and a polycarboxylic acid or acid anhydride.

2. A composition according to claim 1, wherein the palm oil is in an amount ranging from 15 to 85 wt% of the composition of the alkyd.

3. A composition according to claim 1, wherein the polyol is in an amount ranging from 5 to 55 wt% of the composition of the alkyd.

4. A composition according to claim 1, wherein the polycarboxylic acid or acid anhydride is in an amount ranging from 15 to 45 wt% of the composition of the alkyd.

5. A composition according to claim 1, wherein the polyol is any one or more of glycerol, ethylene glycol, 1 , 4-butandiol, propanediol, pentaerythritol, mannitol and sorbitol.

6. A composition according to claim 1, wherein the polycarboxylic acid is any one or more of maleic acid, fumaric acid, trimellitic acid, succinic acid, adipic acid and itaconic acid.

7. A composition according to claim 1, wherein the acid anhydride is phthalic anhydride, maleic anhydride or a combination thereof.

8. A method of producing a plasticiser for polyvinyl chloride (PVC) comprising the steps of:

reacting palm oil with polyol in the presence of an alkaline catalyst at a temperature ranging from 150 to 250°C to obtain a mixture of monoglycerides;

subjecting the mixture of monoglycerides to a polycondensation reaction with polycarboxylic acid or acid anhydride at a temperature between 200-240 °C until the mixture achieves an acid number of 5 to 45 mg KOH/g.