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Coating compositions based on modified phenol-formaldehyde resin and urethane prepolymers
Progress in Organic Coatings 49 (2004) 109–114
Coating compositions based on modified phenol-formaldehyde resin and urethane prepolymers ˙ Anna Zmihorska-Gotfryd Faculty of Chemistry, Rzeszow University of Technology, Rzeszow, Poland Received 23 June 2003; accepted 3 September 2003
Abstract New polymer compositions were synthesised on the base of butyloxylated phenol-formaldehyde resin and three kinds of urethane oligomers. These oligomers were obtained from TDI and selected commercial oligoetherols Rokopol. Coatings based on these compositions were manufactured and their various properties were determined. The coatings exhibited a very good adhesion to metallic substrate, good elasticity and an excellent chemical resistance to selected corrosive media. © 2003 Elsevier B.V. All rights reserved. Keywords: Polymer compositions; Urethane oligomers; Butoxylated phenol-formaldehyde resin
1. Introduction The chemical modification of well-known and widely used polymers gives the possibility of obtaining new materials with advantageous properties and new ranges of applications. With respect to resol phenol-formaldehyde resins this modification is the subject of interest of many investigators [1–3]. Resol phenol-formaldehyde resins (PF) obtained in reaction of condensation of phenol and formaldehyde in alkali environment belong to the oldest synthetic polymers. They are widely used in production of laminates, moulding compositions, glues and coatings [4]. The drawback of these polymers is, after curing, a considerable fragility and a low impact resistance. The chemical structure of phenol-formaldehyde resols, especially the presence of reactive hydroxymethyl groups suggests a possibility of chemical modification enabling the reduction of these unfavourable features. Urethane oligomers with isocyanate end groups may be used as modifiers in this respect [5–7]. Such modified compositions are used as binders for laminates with glass fibre as carrier. The addition of polyurethane enlarges elasticity of the compositions and plays part as a coupling agent, increasing the adhesion of polymer matrix to the carrier [8,9]. PF compositions modified with polyurethanes are also used to obtain foam heat-insulating materials with good ˙ E-mail address: [email protected] (A. Zmihorska-Gotfryd). 0300-9440/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2003.09.002
strength parameters [10–12]. There were also produced as glues for metals with high mechanical strength and thermal resistance [13]. In the literature data can also be found about the use of phenol-formaldehyde compositions, modified by polyurethanes, for obtaining protective coatings [14,15], however, there is a lack of information about their properties. The objective of this work was the synthesis of compositions based on butoxylated PF resin and three kinds of oligomers obtained from 2,4- and 2,6-toluenediisocyanate (TDI) and selected polyetherols and afterwards the determination of the properties of the coatings made from these compositions. The use of etherified resin was forced by the necessity of decreasing its reactivity with oligomer isocyanate groups in order to expand the “life time” of the compositions, i.e. to expand their possible processing time. 2. Experimental 2.1. Materials • Phenol (Fluka AG). • Formaldehyde (37% aq. solution) (POCH Gliwice, Poland). • Ammonia 25% (POCH Gliwice, Poland). • Butan-1-ol (Fluka AG). • TDI (mixture of 2,4- and 2,6-TDI isomers at the ratio of 80 and 20 wt.%, respectively (Aldrich)).
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• Rokopol 7p: oligo(oxypropylene)diol, LOH = 255 mg KOH/g and Mn = 450 g/mol (manufacturer: Zaklady Chemiczne ROKITA, Brzeg Dolny, Poland). • Rokopol 750D: oligo(oxypropylene)diol, LOH = 146 mg KOH/g and Mn = 750 g/mol (manufacturer as above). • Rokopol M-12: oligo(oxypropylene)triol, LOH = 35 mg KOH/g and Mn = 3200 g/mol (manufacturer as above).
Table 1 Physicochemical properties of butoxylated phenol-formaldehyde resin Specific gravity (g/cm3 ) Viscosity (mPa s) Solid mass content (%) Free formaldehyde content (%) Free phenol content (%) Hydroxymethyl groups content, CH2 OH (%)
1.17 379 73.0 0.86 1.79 2.9
2.3. Synthesis of urethane-isocyanate oligomers (PUR) 2.2. Synthesis of butoxylated phenol-formaldehyde resin (PFBu)
The oligomers were manufactured following a known method [16] with three types of oligoetherols: two diols (Rokopol 7p, Rokopol 750D) and one triol (Rokopol M-12). Before the synthesis the oligoetherols were dried in nitrogen atmosphere during 3 h at 110 ◦ C and pressure p = 1.33 kPa. After the reaction was brought to an end, the content of free –NCO groups in the products obtained was analysed and the density and viscosity were measured.
The resin was obtained in a two-stage process consisting of phenol and formaldehyde condensation in alkali medium and next—etherification in the presence of butan-1-ol acidified to pH = 5.8 by phosphoric acid. The synthesis was carried out according to earlier presented paper [3]. Physical and chemical properties of the obtained resin are depicted in Table 1.
Table 2 Physicochemical properties of the urethane oligomers Symbol of oligomer
Amount of TDI (mol)
Amount of oligoetherol (mol)
Specific gravity (g/cm3 )
Viscosity (mPa s)
R7p/TDIa
1.19 1.31 2.4
1 1 1
1.12 1.14 1.16
1555 1980 2200
RD750/TDI RM12/TDI a
Denotes urethane oligomer obtained from Rokopol 7p and TDI.
Fig. 1. IR spectrum of butoxylated phenol-formaldehyde resin.
NCO groups content (%) Measured
Theoretical
4.88 4.95 4.91
5.00 5.00 5.00
˙ A. Zmihorska-Gotfryd / Progress in Organic Coatings 49 (2004) 109–114
Fig. 2. 1 H NMR spectrum of butoxylated phenol-formaldehyde resin (compare Eq. (1)).
Fig. 3. IR spectrum of urethane oligomer R7p/TDI.
111
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112
Fig. 4. 1 H NMR spectrum of urethane oligomer R7p/TDI (compare Eq. (2)).
2.4. Analytical methods employed The –NCO groups were analysed by the usual method which consists in using n-dibutylamine to react with isocyanates. Excess unreacted amine was then titrated with 0.2 M HCl in presence of bromophenol blue indicator. The viscosity was measured by means of the Rheotest 2 rotary viscometer. The density of oligomers was measured by pycnometric method. All results are shown in Table 2. The IR absorption spectra of PFBu resin and urethane oligomers were taken after applying thin films on ZnSe crystals using HATR technique. A FTR-IR PARAGON 1000 spectrometer was used. The 1 H NMR spectra of the products were obtained by means of the NMR 80 MHz Tesla 587A spectrometer. The spectra are shown in Figs. 1–4.
Table 4 Properties of coatings from PFBu modified by RD750/TDI urethane oligomer Coatings properties
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd
Content of RD750/TDI oligomer in composition (%) 5
10
15
20
25
50 8 2 0.95
50 8 1 0.89
50 2 1 0.70
60 2 1 0.68
60 2 1 0.61
a
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
Table 3 Properties of coatings from PFBu modified by R7p/TDI urethane oligomer
Table 5 Properties of coatings from PFBu modified by RM12/TDI urethane oligomer
Coating properties
Coatings properties
Content of R7p/TDI oligomer in composition (%) 5
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd a
50 10 1 0.96
10 50 8 1 0.90
15 50 2 1 0.75
20 50 2 1 0.66
25 50 2 1 0.55
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd a
Content of RD750/TDI oligomer in composition (%) 5
10
15
20
25
50 3 2 0.87
70 2 1 0.66
70 2 1 0.59
70 2 1 0.53
70 2 2 0.40
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
˙ A. Zmihorska-Gotfryd / Progress in Organic Coatings 49 (2004) 109–114
2.5. Preparation of coatings Coating compositions were manufactured using PFBu and the obtained PUR oligomers, the latters dosed in quantities 5; 10; 15; 20; 25% of total mass. The components were well mixed, deaerated in vacuum and applied as 60 m films on glass and metal plates. The coatings were oven-baked for 90 min at 110 ◦ C. The properties of coatings are summarised in Tables 3–5.
3. Discussion of results 3.1. Properties and structure of PFBu resin The properties of butoxylated phenol-formaldehyde resin (Table 1) reveal that the resin is distinguished by a high solid mass content (73%) and a low free monomers content. The resin contains only 0.86% of free formaldehyde and 1.8% of free phenol, that is undoubtedly advantageous in respect to its processing and application. The resin contains also 2.9% of free hydroxymethyl groups. These groups, in the final composition, are partially involved in reaction with isocyanate groups in urethane oligomers, the remaining ones take part in the thermal curing process. The specific absorption bands in the IR spectrum of the resin (Fig. 1) confirm the presence of its typical structural components. They are as follows: aromatic ring, 1594–1605 cm−1 ; hydroxyl groups, 3306 cm−1 ; hydroxyl groups connected with phenyl ring, 1229.4 cm−1 ; hydroxymethyl groups, 993–1023 cm−1 ; methylene linkages, 2873–2959 and 1456–1473 cm; ether linkages, 1069 cm−1 . The band at 751.5 cm−1 indicates the presence of carbon chain due to butan-1-ol. The chemical structure of the resin is also confirmed by 1 H NMR spectrum (Fig. 2), where are indicated the chemical shifts corresponding to the protons from relevant structural segments (Eq. (1)): a
OH
OH b
CH2
e
CH2OH d
c
CH2
CH2
OH
f
O
CH2
CH2
CH2
CH3
(1)
3.2. Physical and chemical properties of urethane oligomers The urethane oligomers ended with isocyanate groups were obtained in polyaddition reaction of the excess of TDI and selected oligoetherols according to the conditions depicted in Table 2. Properties of the oligomers show that their
113
specific gravity is in the range 1.12–1.16 g/cm3 and increases with the increase of molecular weight of the oligoetherol. The same may be observed with respect to their viscosity. The measured free isocyanate groups content is in the range 4.88–4.95% and was somewhat lesser then the predicted, theoretical value. This small difference (1–2%) may be accounted for by a possible inaccuracy of the measurements. The chemical structure of urethane oligomers is confirmed by the spectra IR and 1 H NMR (Figs. 3 and 4). The spectrum of only one type of oligomer is given because the other ones showed a very close resemblance to it. The analysis of the IR spectra of the obtained oligomers shows the presence of the following absorption bands: 1st amide band, 1728 cm−1 ; 2nd amide band, 1537 cm−1 ; –NH– groups in urethane segment, 3297 cm−1 ; –NCO groups, 2265.3 cm−1 ; ethers bridge from oligoetherols, 1080 cm−1 ; aromatic rings, 1520–1617.9 cm−1 ; aromatics rings substituted in position 2,4, 869.9–924.1 cm−1 ; and in position 2,6, 785 cm−1 ; groups –CH2 – and –CH3 , 2868–2931 cm−1 and 1343–1373.7 cm−1 . In the 1 H NMR spectrum (Fig. 4) the chemical shifts corresponding to protons present in the structural components (Eq. (2)) are indicated: a
CH3
O c
b
OCN
NH
C
O
CH
e
CH2
O
CH3 f
d
(2)
3.3. Coatings properties The properties of coatings made from PFBu resin modified by various amounts of the obtained urethane oligomers are shown in Tables 3–5. The coatings have a good impact strength (in a 50–70 cm range). Its highest value corresponds to coatings containing 10–25% of RM12/TDI oligomer. The same coatings have also the lowest hardness that goes down if the amount of this oligomer increases. We may guess that it results from the presence of long ether segments given by Rokopol M12 with great molecular weight (Mn = 3200 g/mol). The lowest impact strength (50 cm) is observed for coatings made with R7p/TDI oligomer, regardless of its amount. This amount, on the other hand, influences the coating hardness, that decreases (from 0.96 to 0.65) if the modifier content increases. All coatings are distinguished by their excellent elasticity. Regardless the modifier type, with contents of 15% or more, the elasticity was equal to 2 mm. The lower modifier contents gave elasticity values of 8 or 10 mm. In most cases the coatings revealed a very good adhesion to substrate, equal to 1 grade in 5-grade full scale. It confirms the earlier literature data that polyurethanes increase the adhesion of polymer coatings to metallic substrates.
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Table 6 Chemical resistance of cured PFBu-RD750/TDI (5)a composition after 1 week exposition to the selected corrosive media at temperature 23 ± 1 ◦ C (according to Polish Standard PN-78/C-89067) Corrosive medium
Water (cold)
10% HCl
3% H2 SO4
1% NaOH
5% NaOH
10% NH3 (aq.)
10% NaCl
Average rise in wt.% Specimen appearance
+0.45 No changes
+1.20 No changes
+1.10 Tarnish
+1.86 Small wrinkles
+1.54 Small wrinkles
+1.11 Tarnish
+0.78 No changes
a
Denotes composition containing 5% RD750/TDI urethane oligomer.
Table 7 Chemical resistance of cured PFBu-RM12/TDI (20)a composition after 1 week exposition to the selected corrosive media at temperature 23 ± 1 ◦ C (according to Polish Standard PN-78/C-89067) Corrosive medium
Water (cold)
10% HCl
3% H2 SO4
1% NaOH
5% NaOH
10% NH3 (aq.)
10% NaCl
Average rise in wt.% Specimen appearance
+0.43 No changes
+1.12 No changes
+0.95 Tarnish
+1.55 Tarnish
+1.38 Small wrinkles
+0.98 Tarnish
+0.77 No changes
a
Denotes composition containing 20% urethane oligomer RM12/TDI.
3.4. Chemical resistance of the coatings The chemical resistance of the coatings has been also investigated. For the sake of shortness of the paper, the relevant results are presented for only two kinds of compositions. The first composition comprised 5% of urethane oligomer RD750/TDI and 95% of PFBu resin (Table 6), the second one 20% of oligomer RM12/TDI and 80% of the above resin (Table 7). It was found that the prepared coatings revealed a very good resistance to the selected corrosive media. During the 1-week exposure to acid media the specimen gained in weight by only ca 1%, whereas in alkali media the rise in their weight was somewhat greater (ca 1.5%). The specimen showed a low soakability in cold water (∼0.49%) and a good resistance to 10% solution of natrium chloride. After the week exposure the outer appearance of the specimen showed practically no change. Only in the case of exposure to 5% NaOH solution, small wrinkles were observed on the specimen surface.
4. Conclusions New varnish compositions were manufactured by modifying butoxylated phenol-formaldehyde resin by selected urethane oligomers ended with isocyanate groups.
The coatings exhibited very good adhesion to metallic substrate and good impact strength and elasticity. The very good chemical resistance of these compositions allows for using them as protective coatings in aggressive environments. References [1] M. Turnen, L. Alvila, J. Rainio, J. Appl. Polym. Sci. 88 (2) (2003) 582–588. [2] L. Gao, Y. Liu, L. Yang, Polym. Degrad. Stabil. 63 (1999) 19– 22. ˙ [3] A. Zmihorska-Gotfryd, Polimery (Warsaw) 45 (10) (2000) 687– 692. [4] A. Knop, L.A. Pilato, Phenolic Resin, Chemistry, Applications and Performance, Springer, Berlin, 1985. [5] JP 6,200,515 (1987). [6] US 4,546,124 (1985). [7] JP 06,220,153 (1994). [8] H.-D. Wu, C.-C. Ma, M.-S. Lee, Y.-D. Wu, Angew. Makromol. Chem. 235 (1996) 35–45. [9] US 5,534,302 (1996). [10] EP 125,677 (1984). [11] JP 06,220,154 (1994). [12] US 4,568,704 (1986). [13] DE 4,309,079 (1994). [14] GB 2,155,487 (1985). [15] Z. Wirpsza, B. Sulecka, Polimery (Warsaw) 31 (1) (1986) 12–14. ˙ [16] P. Król, A. Zmihorska-Gotfryd, Polimery (Warsaw) 45 (11–12) (2000) 775–785.
Coating compositions based on modified phenol-formaldehyde resin and urethane prepolymers ˙ Anna Zmihorska-Gotfryd Faculty of Chemistry, Rzeszow University of Technology, Rzeszow, Poland Received 23 June 2003; accepted 3 September 2003
Abstract New polymer compositions were synthesised on the base of butyloxylated phenol-formaldehyde resin and three kinds of urethane oligomers. These oligomers were obtained from TDI and selected commercial oligoetherols Rokopol. Coatings based on these compositions were manufactured and their various properties were determined. The coatings exhibited a very good adhesion to metallic substrate, good elasticity and an excellent chemical resistance to selected corrosive media. © 2003 Elsevier B.V. All rights reserved. Keywords: Polymer compositions; Urethane oligomers; Butoxylated phenol-formaldehyde resin
1. Introduction The chemical modification of well-known and widely used polymers gives the possibility of obtaining new materials with advantageous properties and new ranges of applications. With respect to resol phenol-formaldehyde resins this modification is the subject of interest of many investigators [1–3]. Resol phenol-formaldehyde resins (PF) obtained in reaction of condensation of phenol and formaldehyde in alkali environment belong to the oldest synthetic polymers. They are widely used in production of laminates, moulding compositions, glues and coatings [4]. The drawback of these polymers is, after curing, a considerable fragility and a low impact resistance. The chemical structure of phenol-formaldehyde resols, especially the presence of reactive hydroxymethyl groups suggests a possibility of chemical modification enabling the reduction of these unfavourable features. Urethane oligomers with isocyanate end groups may be used as modifiers in this respect [5–7]. Such modified compositions are used as binders for laminates with glass fibre as carrier. The addition of polyurethane enlarges elasticity of the compositions and plays part as a coupling agent, increasing the adhesion of polymer matrix to the carrier [8,9]. PF compositions modified with polyurethanes are also used to obtain foam heat-insulating materials with good ˙ E-mail address: [email protected] (A. Zmihorska-Gotfryd). 0300-9440/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2003.09.002
strength parameters [10–12]. There were also produced as glues for metals with high mechanical strength and thermal resistance [13]. In the literature data can also be found about the use of phenol-formaldehyde compositions, modified by polyurethanes, for obtaining protective coatings [14,15], however, there is a lack of information about their properties. The objective of this work was the synthesis of compositions based on butoxylated PF resin and three kinds of oligomers obtained from 2,4- and 2,6-toluenediisocyanate (TDI) and selected polyetherols and afterwards the determination of the properties of the coatings made from these compositions. The use of etherified resin was forced by the necessity of decreasing its reactivity with oligomer isocyanate groups in order to expand the “life time” of the compositions, i.e. to expand their possible processing time. 2. Experimental 2.1. Materials • Phenol (Fluka AG). • Formaldehyde (37% aq. solution) (POCH Gliwice, Poland). • Ammonia 25% (POCH Gliwice, Poland). • Butan-1-ol (Fluka AG). • TDI (mixture of 2,4- and 2,6-TDI isomers at the ratio of 80 and 20 wt.%, respectively (Aldrich)).
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110
• Rokopol 7p: oligo(oxypropylene)diol, LOH = 255 mg KOH/g and Mn = 450 g/mol (manufacturer: Zaklady Chemiczne ROKITA, Brzeg Dolny, Poland). • Rokopol 750D: oligo(oxypropylene)diol, LOH = 146 mg KOH/g and Mn = 750 g/mol (manufacturer as above). • Rokopol M-12: oligo(oxypropylene)triol, LOH = 35 mg KOH/g and Mn = 3200 g/mol (manufacturer as above).
Table 1 Physicochemical properties of butoxylated phenol-formaldehyde resin Specific gravity (g/cm3 ) Viscosity (mPa s) Solid mass content (%) Free formaldehyde content (%) Free phenol content (%) Hydroxymethyl groups content, CH2 OH (%)
1.17 379 73.0 0.86 1.79 2.9
2.3. Synthesis of urethane-isocyanate oligomers (PUR) 2.2. Synthesis of butoxylated phenol-formaldehyde resin (PFBu)
The oligomers were manufactured following a known method [16] with three types of oligoetherols: two diols (Rokopol 7p, Rokopol 750D) and one triol (Rokopol M-12). Before the synthesis the oligoetherols were dried in nitrogen atmosphere during 3 h at 110 ◦ C and pressure p = 1.33 kPa. After the reaction was brought to an end, the content of free –NCO groups in the products obtained was analysed and the density and viscosity were measured.
The resin was obtained in a two-stage process consisting of phenol and formaldehyde condensation in alkali medium and next—etherification in the presence of butan-1-ol acidified to pH = 5.8 by phosphoric acid. The synthesis was carried out according to earlier presented paper [3]. Physical and chemical properties of the obtained resin are depicted in Table 1.
Table 2 Physicochemical properties of the urethane oligomers Symbol of oligomer
Amount of TDI (mol)
Amount of oligoetherol (mol)
Specific gravity (g/cm3 )
Viscosity (mPa s)
R7p/TDIa
1.19 1.31 2.4
1 1 1
1.12 1.14 1.16
1555 1980 2200
RD750/TDI RM12/TDI a
Denotes urethane oligomer obtained from Rokopol 7p and TDI.
Fig. 1. IR spectrum of butoxylated phenol-formaldehyde resin.
NCO groups content (%) Measured
Theoretical
4.88 4.95 4.91
5.00 5.00 5.00
˙ A. Zmihorska-Gotfryd / Progress in Organic Coatings 49 (2004) 109–114
Fig. 2. 1 H NMR spectrum of butoxylated phenol-formaldehyde resin (compare Eq. (1)).
Fig. 3. IR spectrum of urethane oligomer R7p/TDI.
111
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112
Fig. 4. 1 H NMR spectrum of urethane oligomer R7p/TDI (compare Eq. (2)).
2.4. Analytical methods employed The –NCO groups were analysed by the usual method which consists in using n-dibutylamine to react with isocyanates. Excess unreacted amine was then titrated with 0.2 M HCl in presence of bromophenol blue indicator. The viscosity was measured by means of the Rheotest 2 rotary viscometer. The density of oligomers was measured by pycnometric method. All results are shown in Table 2. The IR absorption spectra of PFBu resin and urethane oligomers were taken after applying thin films on ZnSe crystals using HATR technique. A FTR-IR PARAGON 1000 spectrometer was used. The 1 H NMR spectra of the products were obtained by means of the NMR 80 MHz Tesla 587A spectrometer. The spectra are shown in Figs. 1–4.
Table 4 Properties of coatings from PFBu modified by RD750/TDI urethane oligomer Coatings properties
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd
Content of RD750/TDI oligomer in composition (%) 5
10
15
20
25
50 8 2 0.95
50 8 1 0.89
50 2 1 0.70
60 2 1 0.68
60 2 1 0.61
a
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
Table 3 Properties of coatings from PFBu modified by R7p/TDI urethane oligomer
Table 5 Properties of coatings from PFBu modified by RM12/TDI urethane oligomer
Coating properties
Coatings properties
Content of R7p/TDI oligomer in composition (%) 5
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd a
50 10 1 0.96
10 50 8 1 0.90
15 50 2 1 0.75
20 50 2 1 0.66
25 50 2 1 0.55
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
strengtha
Impact (cm) Elasticityb (mm) Cross-cut adhesionc (grades) Hardnessd a
Content of RD750/TDI oligomer in composition (%) 5
10
15
20
25
50 3 2 0.87
70 2 1 0.66
70 2 1 0.59
70 2 1 0.53
70 2 2 0.40
Falling-weight test according to EN ISO 6272:1994. Elasticity by bend test (cylindrical mandrel) according to EN ISO 1519:2000. c Cross-cut adhesion according to EN ISO 2409:1992. d Hardness by Pendulum Dumping Test according EN ISO 1522:2001. b
˙ A. Zmihorska-Gotfryd / Progress in Organic Coatings 49 (2004) 109–114
2.5. Preparation of coatings Coating compositions were manufactured using PFBu and the obtained PUR oligomers, the latters dosed in quantities 5; 10; 15; 20; 25% of total mass. The components were well mixed, deaerated in vacuum and applied as 60 m films on glass and metal plates. The coatings were oven-baked for 90 min at 110 ◦ C. The properties of coatings are summarised in Tables 3–5.
3. Discussion of results 3.1. Properties and structure of PFBu resin The properties of butoxylated phenol-formaldehyde resin (Table 1) reveal that the resin is distinguished by a high solid mass content (73%) and a low free monomers content. The resin contains only 0.86% of free formaldehyde and 1.8% of free phenol, that is undoubtedly advantageous in respect to its processing and application. The resin contains also 2.9% of free hydroxymethyl groups. These groups, in the final composition, are partially involved in reaction with isocyanate groups in urethane oligomers, the remaining ones take part in the thermal curing process. The specific absorption bands in the IR spectrum of the resin (Fig. 1) confirm the presence of its typical structural components. They are as follows: aromatic ring, 1594–1605 cm−1 ; hydroxyl groups, 3306 cm−1 ; hydroxyl groups connected with phenyl ring, 1229.4 cm−1 ; hydroxymethyl groups, 993–1023 cm−1 ; methylene linkages, 2873–2959 and 1456–1473 cm; ether linkages, 1069 cm−1 . The band at 751.5 cm−1 indicates the presence of carbon chain due to butan-1-ol. The chemical structure of the resin is also confirmed by 1 H NMR spectrum (Fig. 2), where are indicated the chemical shifts corresponding to the protons from relevant structural segments (Eq. (1)): a
OH
OH b
CH2
e
CH2OH d
c
CH2
CH2
OH
f
O
CH2
CH2
CH2
CH3
(1)
3.2. Physical and chemical properties of urethane oligomers The urethane oligomers ended with isocyanate groups were obtained in polyaddition reaction of the excess of TDI and selected oligoetherols according to the conditions depicted in Table 2. Properties of the oligomers show that their
113
specific gravity is in the range 1.12–1.16 g/cm3 and increases with the increase of molecular weight of the oligoetherol. The same may be observed with respect to their viscosity. The measured free isocyanate groups content is in the range 4.88–4.95% and was somewhat lesser then the predicted, theoretical value. This small difference (1–2%) may be accounted for by a possible inaccuracy of the measurements. The chemical structure of urethane oligomers is confirmed by the spectra IR and 1 H NMR (Figs. 3 and 4). The spectrum of only one type of oligomer is given because the other ones showed a very close resemblance to it. The analysis of the IR spectra of the obtained oligomers shows the presence of the following absorption bands: 1st amide band, 1728 cm−1 ; 2nd amide band, 1537 cm−1 ; –NH– groups in urethane segment, 3297 cm−1 ; –NCO groups, 2265.3 cm−1 ; ethers bridge from oligoetherols, 1080 cm−1 ; aromatic rings, 1520–1617.9 cm−1 ; aromatics rings substituted in position 2,4, 869.9–924.1 cm−1 ; and in position 2,6, 785 cm−1 ; groups –CH2 – and –CH3 , 2868–2931 cm−1 and 1343–1373.7 cm−1 . In the 1 H NMR spectrum (Fig. 4) the chemical shifts corresponding to protons present in the structural components (Eq. (2)) are indicated: a
CH3
O c
b
OCN
NH
C
O
CH
e
CH2
O
CH3 f
d
(2)
3.3. Coatings properties The properties of coatings made from PFBu resin modified by various amounts of the obtained urethane oligomers are shown in Tables 3–5. The coatings have a good impact strength (in a 50–70 cm range). Its highest value corresponds to coatings containing 10–25% of RM12/TDI oligomer. The same coatings have also the lowest hardness that goes down if the amount of this oligomer increases. We may guess that it results from the presence of long ether segments given by Rokopol M12 with great molecular weight (Mn = 3200 g/mol). The lowest impact strength (50 cm) is observed for coatings made with R7p/TDI oligomer, regardless of its amount. This amount, on the other hand, influences the coating hardness, that decreases (from 0.96 to 0.65) if the modifier content increases. All coatings are distinguished by their excellent elasticity. Regardless the modifier type, with contents of 15% or more, the elasticity was equal to 2 mm. The lower modifier contents gave elasticity values of 8 or 10 mm. In most cases the coatings revealed a very good adhesion to substrate, equal to 1 grade in 5-grade full scale. It confirms the earlier literature data that polyurethanes increase the adhesion of polymer coatings to metallic substrates.
˙ A. Zmihorska-Gotfryd / Progress in Organic Coatings 49 (2004) 109–114
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Table 6 Chemical resistance of cured PFBu-RD750/TDI (5)a composition after 1 week exposition to the selected corrosive media at temperature 23 ± 1 ◦ C (according to Polish Standard PN-78/C-89067) Corrosive medium
Water (cold)
10% HCl
3% H2 SO4
1% NaOH
5% NaOH
10% NH3 (aq.)
10% NaCl
Average rise in wt.% Specimen appearance
+0.45 No changes
+1.20 No changes
+1.10 Tarnish
+1.86 Small wrinkles
+1.54 Small wrinkles
+1.11 Tarnish
+0.78 No changes
a
Denotes composition containing 5% RD750/TDI urethane oligomer.
Table 7 Chemical resistance of cured PFBu-RM12/TDI (20)a composition after 1 week exposition to the selected corrosive media at temperature 23 ± 1 ◦ C (according to Polish Standard PN-78/C-89067) Corrosive medium
Water (cold)
10% HCl
3% H2 SO4
1% NaOH
5% NaOH
10% NH3 (aq.)
10% NaCl
Average rise in wt.% Specimen appearance
+0.43 No changes
+1.12 No changes
+0.95 Tarnish
+1.55 Tarnish
+1.38 Small wrinkles
+0.98 Tarnish
+0.77 No changes
a
Denotes composition containing 20% urethane oligomer RM12/TDI.
3.4. Chemical resistance of the coatings The chemical resistance of the coatings has been also investigated. For the sake of shortness of the paper, the relevant results are presented for only two kinds of compositions. The first composition comprised 5% of urethane oligomer RD750/TDI and 95% of PFBu resin (Table 6), the second one 20% of oligomer RM12/TDI and 80% of the above resin (Table 7). It was found that the prepared coatings revealed a very good resistance to the selected corrosive media. During the 1-week exposure to acid media the specimen gained in weight by only ca 1%, whereas in alkali media the rise in their weight was somewhat greater (ca 1.5%). The specimen showed a low soakability in cold water (∼0.49%) and a good resistance to 10% solution of natrium chloride. After the week exposure the outer appearance of the specimen showed practically no change. Only in the case of exposure to 5% NaOH solution, small wrinkles were observed on the specimen surface.
4. Conclusions New varnish compositions were manufactured by modifying butoxylated phenol-formaldehyde resin by selected urethane oligomers ended with isocyanate groups.
The coatings exhibited very good adhesion to metallic substrate and good impact strength and elasticity. The very good chemical resistance of these compositions allows for using them as protective coatings in aggressive environments. References [1] M. Turnen, L. Alvila, J. Rainio, J. Appl. Polym. Sci. 88 (2) (2003) 582–588. [2] L. Gao, Y. Liu, L. Yang, Polym. Degrad. Stabil. 63 (1999) 19– 22. ˙ [3] A. Zmihorska-Gotfryd, Polimery (Warsaw) 45 (10) (2000) 687– 692. [4] A. Knop, L.A. Pilato, Phenolic Resin, Chemistry, Applications and Performance, Springer, Berlin, 1985. [5] JP 6,200,515 (1987). [6] US 4,546,124 (1985). [7] JP 06,220,153 (1994). [8] H.-D. Wu, C.-C. Ma, M.-S. Lee, Y.-D. Wu, Angew. Makromol. Chem. 235 (1996) 35–45. [9] US 5,534,302 (1996). [10] EP 125,677 (1984). [11] JP 06,220,154 (1994). [12] US 4,568,704 (1986). [13] DE 4,309,079 (1994). [14] GB 2,155,487 (1985). [15] Z. Wirpsza, B. Sulecka, Polimery (Warsaw) 31 (1) (1986) 12–14. ˙ [16] P. Król, A. Zmihorska-Gotfryd, Polimery (Warsaw) 45 (11–12) (2000) 775–785.