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The effect of antioxidants for thermostablization upon high Density polyethylene by using various Techniques Mahdi M. Al...

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The effect of antioxidants for thermostablization upon high Density polyethylene by using various Techniques Mahdi M. Almaky1, Moussa I. Khlifa1, Saleh N. Ahdiri1, and Gamal J. Aboulgasem2. 1. Department of Chemistry, Sebha University, Sebha - Libya. 2. Department of Chemistry, Alzawia University, Alzawia - Libya.

Abstract:Themost important additives of thermostabilization of High Density Polyethylene (HDPE) realized through the action of primary antioxidantssuch as phenolic antioxidants and secondary antioxidants as aryl phosphates. The efficiency of two secondary antioxidants, commercially named Irgafos 168 and Weston 399,investigated by using different physical, mechanical, spectroscopic and colorimetric methods. The effect of both antioxidants on the processing stability and long-term stability of HDPE produced in RasLanuf Oil and Gas processing Company were thatmeasured and compared. The combination of antioxidants, Irgafos 168 with Irganox 1010,as used in smaller concentration, results to cause a synergetic effect against thermo-oxidation and protect better than the combination of Weston 399 with Irganox 1010 against the colour change at processing temperature and during long-term oxidation process. Key wards: FTIR, DSC, oven aging, antioxidant. Introduction Virtually all polymeric materials undergo oxidation reactions. Oxidation can occur in every stage of the life cycle of the polymer, i.e. during manufacturing, storage of the material or during processing,as well as end use.Typical manifestation of oxidation of polyolefins can be change of appearance and loss of mechanical properties such as elongation, tensile strength, and flexibility. Antioxidants protect polyolefin against oxidation by controlling molecular weight changes that leads to loss of physical and mechanical properties. HDPE cannotapplication without the addition of suitable stabilizers. The type and concentration of additives required to stabilize the polymer adequately will depend on the severity of processing conditions, services environment, the thickness of the fabricated pieces, mechanical strain, chemical environment and the duration of useful life desired.[1]

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The thermostabilization of HDPE is realised through the action of a combination of phosphite processing stabilizer and a phenolic antioxidant used as long-term heat stabilizer. Compatibility is a key parameter in choosing a stabilizer for a given resin of application. The most important secondary antioxidant, named preventives antioxidants are the phosphorous acids esters. Phosphite or phosphonite type secondary antioxidants are generally add to phenolic antioxidant to reduce crosslinking and chain scission during processing steps at elevated temperature. A brief description of the most used secondary antioxidant will showing below as following: Tris(nonyl-phenyl)phosphite – Weston 399 or Irgafos TNPP [2] is used from a long time ago as a stabilizer for styrene-butadiene rubbers. It is a

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viscous

liquid

with

the

(H C

molecular

O)

19 9

P

3

structure:

Fig. 1Tris(nonyl – phenyl)phosphite

Irgafos 168, Tris(2, 4-ditertbutyl)phosphite, is a white powder with melting point 180 – 185 °C and the molecular structure: (tBu

O)

3

P

Secondary antioxidants have the ability to yield non-radicals products and therefore, frequently called hydro peroxide decomposers. Aryl phosphates are able to form an efficient chain-terminating agent in

.

reaction with ROO radicals [3]. They react with simple alkyl-peroxylradicals, which are capable of terminating the antioxidation chain.

tBu

Fig.2 Tris(2, 4-di-tertbutyl)phosphite

.

ROO + P(OAr)3

.

RO + P(OAr)3

.

.

ROO + ArO

.

.

-

HDPE is normally processing at temperature between 200 and 280 °C. If insufficiently stabilized, polyethylene will be degraded. Primary antioxidant, hindered phenolic antioxidants (Irganox 1010, Irganox1076),contributes significantly

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mechanism proceeds according to a non-radical mechanism:

-

RO + HO-P+(OAr)3

Processing stabilization of HDPE; Long – term heat stabilization of HDPE.

-

.

ROP(OAr)2 + OAr

Inactive products

Furthermore, they act as metal complex forming agents blocking metal ions, which are cause chain initiation, and branching by reaction with ROOH and RH [3]. They are two important types of HDPE stabilization: -

RO + O=P(OAr)3

ROP (OAr)3

In addition, organic phosphates react with hydroperoxides to form phosphates and alcohols. The ROOH + P(Oar 3

.

ROOP (OAr)3

ROH + O=P(OAr)3

to reducing polymer degradation and thus to maintaining the melt stability and measured by melt flow index. [1] Phosphiteas secondary antioxidant (Weston 399,Irgafos 168 )are generally added to phenolic antioxidants to reduce cross linking during processing steps at elevated temperature and thus to obtain easier processing and less gel formation.[3] The usual method for assessing the effectiveness of antioxidant under processing conditions is the multiple extrusion test in which change in melt flow index and colour of the extruded material are determined after each of five successive extrusions [4]. Besides providing viscosity stability to the polymer, melt during processing, antioxidants should not discolour the

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polymer and should protect against colour change processing temperature. This is particularly important to the packaging. Hindered phenolic antioxidants are the most important additives in long – term heat stabilization of HDPE. HDPE leads itself to such application as boilable food packages.For these types of high temperature application, a stabilizer has to be able to provide an extended useful life to fabricate product. Manymoulding and packaging film application using HDPE must withstand boiling water as well as autoclave sterilization temperature. The effectiveness of antioxidant under conditions of actual use i.e. as longterm heat stabilizers determined almost exclusively by mean of oven aging test, at temperature below the melting point of polymer [5]. Discoloration during oven aging and significant change of mechanical properties such as tensile strength andelongation, as a function of aging time, are often used as test criteria.[6] The objective of this experiment was to test a new secondary antioxidant

supplied by cyba-giegy,irgafos 168. The efficiency of this antioxidant comparedwith the efficiency of Weston 399, which is still using for obtaining HDPE film grade in RasLanufoil and gas processing co. The main disadvantages presented by the Weston 399 are as the following: -

-

-

It is viscous liquid which is hardly manipulated and donated in full-scalemanufacture; It is high hygroscopic substance, which is decompose by exposure to water or high humidity. The phosphorous acid formed by alcoholiseis corrosive to processing equipments,particularly at high temperature. Furthermore,hydrolyzed phosphates do not contribute to the melt stability; FDA accepts Weston 399 as an indirect food additive.

The preferred physical form of an additive is a non-viscous liquid or a free flowing powder [7].

Experimental: There are three methods used for characterize the degradation of this type of polyethylene. A) Measuring the changes in melt index after each of five successive extrusions, at 190°C,by using a Ray Ran melt indexer apparatus; B) Retention of physical properties of 0.7 mm HDF plaques placed in a forced draft oven at 100°C, using a LR 5K Lloyd instruments; C) Spectroscopic and thermo calorimetrical measurements using a PYE Unicam SP 3-200 IR spectrophotometer and PL polymer

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laboratories differential scanning calorimeterrespectively. The base resin for experiments was polyethylene grade resin DGX 5117, in which obtained through Union Carbide method by using catalysttype S2 (such as a catalyst) in RasLanuf oil and gas processing Company. Irganox 1010 and Irgafos168, both supplied by Ciba-Giegyand were mixed with polyethylene resin by tworoll mill at 180°C. The plaquesattained by compression moulding at a platen pressure of 2000 psi and temperature of 200 °C.

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For FTIR spectroscopy measurements, one sample of HDPE containing only zincstearate placed in the reference beam, and samples with

additives HDPE that placed in the other beam. The stabilization formulas are depicts in Table 1.

Table 1: Composition of additives blended with HDPE DGX 5117

Sample No.

Polymer

1. 2. 3. 4. 5.

DGX-5117 DGX-5117 DGX-5117 HDF-5116 – Lot 051A/2002 HDF-5116 – Lot 137A/2001

Primery antioxidant (Irganox 1010), (%) 0.075 0.050 0.080 Master Batch (LFMB-3)

Secondary antioxidant (Irgafos 168), (%)

Lubricating and antiacid additive (Zinc stearate), (%)

0.075 0.100 0.120(Weston) Master Batch

0.15 0.15 0.15 0.20 MB

Results and Discussions: A) Measuring the change in melt index after multiple extrusions: The multiple extrusion approach used to optimize a processing stabilizer formulation to obtain the most costefficient product suitable for one under the wide variety of processing conditions found in today’s markets. Process stability was determined by following change in melt index, as the polymer successively re-extruded through melt Flow Indexer at a

temperature of190°C and a dead weight of 21.6kg. For this test,a comparison of the polyethylene in which used Weston 399 (sample no. 4) with the formulation in which used a smaller concentration of Irgafos 168 (sample no.3) takes place. Polyethylene with zinc stearate (sample no.1) used as a reference.The data presented in Figure 1. As can be observed, both formulas 3 and 4 have convergent values, i.e., it can be with comparisonbehaviour.

Figure 1: Variation of Melt Flow Index with number of extrusions.

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The effect of antioxidants for thermostablization............................................. Almaky et al..

B) Retention of physical properties after oven aging at 100°C: As failure criterion for tensile properties and colour is taken 50%-retained properties (Figures 2) .These results are present in Table 2.

Figure 2: Variation of colour with the exposure time. Table 2: The properties of HDF exposed in oven aging at 100 °C. No

Content,

Time,

MI,

MFI,

1.

% 0.15 Zn St

Week Initial 4 5 6 Initial 4 5 6 15 Initial 4 5 6 15 Initial 4 5 6 15 Initial 4 5 6 15

g/10min. 0.05 0.15 0.15 0.15 0.15 0.15 0.11 0.10 0.10 0.10 0.10 0.11 0.10 0.10 0.11 0.09 0.16 0.14 0.14 0.13 0.14

g/10min. 8.5 13.6 13.9 13.9 14.0 13.0 11.4 11.0 11.0 11.0 11.0 11.1 12.0 11.0 11.0 11.0 16.0 16.0 16.0 16.0 16.0

2.

3.

0.15 Zn st 0.075 Ir1010 0.075 Irg168 0.15 Zn st 0.05 Ir-1010 0.10 Irg-168

4.

0.20 Zn st 0.08 Ir-1010 0.012 W399

5.

0.20 LFMB3

From those data, it can observed those smaller concentrationsofIrganox 1010 (0.05%) and Irgafos 168 (0.10%)

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MFR

170 91 95 93 93 89 104 107 100 109 112 104 122 113 107 117 100 116 123 113

Stress at Stress at Elongat yield, break, -ion, 2 2 N/mm N/mm % 24 29 1053 24 36 1190 24 32 721 24 28 647 25 25 612 25 25 566 23 36 1154 24 34 702 25 33 686 24 31 666 25 31 586 23 35 1129 25 35 752 25 25 31 676 25 28 523 24 34 1193 23 29 707 25 28 677 24 26 683 25 28 600

gave the same properties like the polyethylene HDF 5116 from Lot No: 051A/2002 prepared with 0.08%

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Color

85 47 37 34 70 48 43 42 34 84 75 71 70 66 77 60 58 57 49 76 72 66 69 60

The effect of antioxidants for thermostablization............................................. Almaky et al..

Irganox 1010 and 0.12% Weston 399 and it is comparable with the polyethylene obtainedby using master batch for thermostabilization. Moreover, the colour after 6 weeks exposure in oven is much better than for composition with Weston 399 and approximately the same value with sample no.5. C. Spectroscopic and thermo calorimetric measurements DSC has made the Oxidation Induction Time (OIT) measurements, at 200 °C (ASTM D-3895) with the polymer in molten state. The OIT method

produces rapid results, which however do not correlate with the corresponding oven-aging data gathered from the polymer in the solid state. Accelerated test in the melt can be usefulfor quality control purposes (constant polymer/stabilizer system). However, OIT measurements do not permit selection of a stabilizer formulation with respect to its performance under actual end-use conditions. The results of OIT measurements for sample formulations are present in Table 3 and one example in Figure 3.

Figure 3: Measuring of OIT for sample of HDPE containing (0.5% Irganox 1010, 0.1% Irgafos168 and 0.15% Zn. St.) after 15 weeks exposure in oven at 100 °C.

Table 3: OIT- DSC, in oxygen, at 200 °C. Sample No.

Stabilization

2

0.15%-Zn st 0.075%-Irganox 1010 0.075%-Irgafos 168 0.15%-Zn st 0.05%-Irganox 1010 0.10%-Irgafos 168 0.20%-Zn st 0.08%-Irganox 1010 0.12%-Weston 399 0.2%-Master batch

3

4

5

From those data, it could observed also that Irganox 1010 and Irgafos 168 composition have a synergistic effect.

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OIT-initial, minutes 8.46

OIT-after weeks, Minutes 9.18

6 OIT-after weeks, minutes 7.56

13.70

12.62

10.32

16.60

14.43

11.69

6.53

8.88

5.55

15

This effect is more pronounce with the increasing of amount of Irgafos 168 reported to Irganox 1010.

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The effect of antioxidants for thermostablization............................................. Almaky et al..

FTIR spectroscopy measurements show the absorbance beaks whichspecific for Irganox 1010, Irgafos 168 and Weston 399.As it can be observed from Figure 4, these spectra absorbed by functional groups are :

-Irganox 1010 – 1745 cm-1, -Irgafos 168 – 1189; 1176; 1065 cm-1, -Weston 399 – 1186; 11651 cm-1, -Zn St – 1247; 1083 cm-1.

Figure 4: FTIR Spectrum for samples 1 -5 used in the experiment. Polyethylene without additives used as a reference sample. It observed that the concentration of Irganox 1010 remained in the samples after exposure in the oven. Polyethylene presents also as absorbance peak in the region 1717 –

1760 cm-1. Therefore, we have to subtract its absorbance at 1745 cm-1 from the absorbance of Irganox 1010. The results aredescribing in Table 4 and one example is presenting in Figure 5.

Table 4: The consumption of Irganox 1010 during the exposure in oven. Sample No. 2

3

4 5

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Stabilization formula 0.15%-Zn St 0.075%-Irganox 1010 0.075-Irgafos 168 0.15%-Zn St 0.05%-Irganox 1010 0.10-Irgafos 168 0.20%-Zn St 0.08%-Irganox 1010 0.12-Weston 399 0.2% Master batch

Irganox 1010 content After 4 After 6 Initial weeks weeks 0.085

0.06

0.055

0.049

0.041

0.040

0.110

0.100

0.074

0.063

0.050

0.040

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The effect of antioxidants for thermostablization............................................. Almaky et al..

Figure 5: spectra forIrganox 1010 consumption after 6 weeks exposure in oven. We point out that the consumption of Irganox 1010 in the sample with Weston 399 is faster than in the case of Irganox 1010/Irgafos 168. This fact is also correlated with the decreasing of mechanical properties of the sample prepared with Weston 399 was faster than those prepared with Irgafos 168.

In figure 6, the spectrum of polyethylene without antioxidants before and after four weeks exposure in ovenwas registered. The disparities of peaks from 3445 cm-1, developing of hydroperoxides at 3547 cm-1, and modification of carbonyl group at 1717 cm-1 are noted.

Figure 6: FTIR spectrum of HDPE, DGX-5177, without antioxidants before and after 4 weeks.

Figure 7: FTIR spectrum of HDPE contains (0.05 % irganox 1010, 0.1 % Irgafos 168 and 0.15 % Zn-St.) before and after 4 and 5 weeks exposure in oven at 100 °C.

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The effect of antioxidants for thermostablization............................................. Almaky et al..

In Figure 7, an example of samples contain antioxidants after 5 weeks of exposure in oven at 100 °C is present.

In those samples, modifications after 6 exposure.

no such weeks of

Conclusion: The combination of change at processing temperature and Irgafos168/Irganox1010 results in a during long-term oxidation process. synergistic effect better than the The efficiency of combination Irgafos combination of Weston 168 /Irganox 1010 increased for a 399/Irganox1010.Blend of irgafos1010 report between additives of 2:1.The show superiority over the primary increasing of thoseconcentrations of antioxidant alone. antioxidants in 2:1 report produces Irgafos is the only phosphiniteimprovementsof the properties. processing stabilizer with sufficient For a product with a recycling potential hydrolytic stability for trouble – free and injection products therefore it usage and acceptance for films with could beadvantageous choosing and food contact.Irgafos 168 protect better antioxidant formulation high in than Weston 399 against colour phosphite phenol ratio (4:1). ‫دراسة تأثير مضادات األكسدة على الثبات الحراري للبولي ايثيلين عالي الكثافة‬ ‫باستخدام تقنيات متعددة‬ 2

‫ جمال جمعة أبوالقاسم‬،1‫ صالح ناجي احضيري‬،1‫ موسى ابراهيم خليفة‬،1‫المهدي محمد المكي‬ .‫ الزاوية – ليبيا‬،‫ جامعة الزاوية‬،‫ قسم الكيمياء‬. 2 .‫ سبها – ليبيا‬،‫ جامعة سبها‬،‫ قسم الكيمياء‬.1

‫ يحدث الثبات الحراري للبولي ايثيلين مرتفع الكثافة باستخدام كل من مضادات التأكسد األحادية مثل الفينوالت‬:‫الخالصة‬ .‫ومضادات التأكسد الثانوية مثل مركبات األريل أو األلكيل فوسفات‬ ‫ على‬Irgafos 168 ‫ و‬Weston 399 :‫في هذه الدراسة تم قياس تأثير كل من مضادات التأكسد الثانوية المختلفة‬ ‫ ومقارنة النتائج المتحصل‬،‫الثبات الحراري للبولي ايثيلين مرتفع الكثافة المصنع بشركة راس النوف للنفط والغاز الليبية‬ ‫ وكالوريمترية) والتي أجريت على فترات زمنية تبدأ من بعد‬،‫ طيفية‬،‫ ميكانيكية‬،‫عليها بطرق التحليل المختلفة (فيزيائية‬ .‫التصنيع مباشرة وتمتد الى فترات زمنية متفاوتة‬ ‫( واضافتهما بكميات قليلة لعينات البولي ايثيلين‬Irganox 1010/Irgafos 168) ‫تبين من خالل النتائج أن خلط مادتي‬ ‫( في الحماية من عمليات األكسدة الحرارية والتغير‬Irganox 1010/Weston 399) ‫ينتج عنه نتائج أفضل من خليط‬ .‫ وكذلك الحماية من عمليات األكسدة لفترات طويلة‬،‫في اللون أثناء عمليات التصنيع‬ .‫ مضادات التأكسد‬،‫ البولي ايثيلين‬،‫ الثبات الحراري‬:‫المفاتيح‬

References: [1]R.F.Becker, L.P.J. Burton and S.E. Amos,( 1996 ), Polypropylene Handbook. Ed. by E. P. Moore, Jr. Montell U.S.A., Inc.. [2]Encyclopaedia of Polymer Science and Engineering, (1985), Wiley – Interscience publication, John Wiley and Sons , New York, vol.10 [3]K.Schwatlick , (1983), Pure and Appl. chem., vol. 55, no.10, pp.169. [4] F. K. Meyer, E.Pediazzetti,(1986),LLDPE in Europe

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– world prospective and developments, Madrid, vol. 3-5 . [5] CIBA – Geigy,(1988),Processing and Long Term Heat Stabilization of Polyolefin’sPubl. No 28622/e, Switzerland, Apr. (1988). [6]M. R. Kamal,Weatherability of plastic materials, Applied Polymer Symposium, Ed. Interscience, New York, 1967 - viii + 306 pp. 2745–2746. [7] C.Rawendeal,(1994),Polyme Extrusion,hauser/gardnerpuplicationinc , Cincinnati,pp. 164.

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