CHAPTER 3 POLYURETHANES FROM NOVOLAC RESINS AND POLYOLS

Transcription

1 CHAPTER 3 POLYURETHANES FROM NOVOLAC RESINS AND POLYOLS

2 INTRODUCTION Novolac resins and polyols prepared were used as co-reactant in the synthesis of polyurethanes. A variety of polyurethanes having varying mechanical properties, fire-resistant capacity, mouldability, adhesive character and laminates have been developed by many researchers. Polyols of phenol-formaldehyde resins self curable at ambient temperature or curable by amines has been reported'. Synthesis and curing behaviour of a crosslinkable polymer2, polyether3, polyester 4, from cashew nut shell liquid and monomer from cardanol5 have been reported. Phenolic novolac resins mixed with diphenylmethane diisocyanate (MDI) (7) as hardener for heat and moisture resistant epoxy composites has been developed 6. Polyurethane foams have been developed from the benzylic ether of phenolformaldehyde resins and polyisocyanates made from diphenylmethane diisocyanate 7. Fire resistant phenol-formaldehyde, modified polyurethane foam as thermal insulators have also been developed8'9 Phenol-formaldehyde resole resins have been used in developing ink compositions for waterless lithography'. Bisphenol-A (35) based phenolic resin, with polyisocyanate in the presence of an amine was used in inorganic mouldings _(:^_ HOCOH CH3 (35)

3 76 Resistance to fatigue and thermal stability of Phosphorylated cashew nut shell liquid (PCNSL)-modified natural rubber vulcanizate has been reported 15. Natural rubber modified with CNSL and CNSL-formaldehyde resins have also been reported 16. CNSL resins are added to laminates based on phenol-formaldehyde and epoxy resins to reduce brittleness and to improve bonding to laminate substrate ' 7. Bulk polymerised prepolymers for easy dispensability, non-wicking and good dispersion in potting of hollow fibre has been studied by Jayabalan et al' 8. New ferrocene polyurethane block copolymers based on diphenylmethane diisocyanate for use as fire retardant have been synthesised' 9. Phenolic urethane- resins have-also beer studied for use as foundry binders2'21. Urethane pre-polymer blowed with substituted phenol was used as flock adhesive 22. Sitaraman and Chaterjee prepared 23 pressure sensitive adhesives from 3-pentadecyl phenol (hydrogenated cardanol). Reaction of polyisocyanates with a mixture of benzyl ether type phenolic resin (novolac) and hydroxyl terminated polyesters in the presence of blowing agents and catalysts to form heat decomposable fire-resistant phenolic urethane foam having good mouldability and mechanical properties has been developed 24. Varnish for fire-resistant laminate was developed from phenol-formaldehyde resin, ammonia and toluene dilsocyanate, (TDI) (5)-based polyurethane s 25. Hiroshi et at prepared 26 varnish from CNSL - formaldehyde resin using an isocyanate crosslinking agent (Burnock D 75). Auto-oxidation polymerization of Polyurethane films based on cardanol, glycol and toluene diisocyanate

4 77 catalyzed by cobalt salt have also been studied 27. Sailan has prepared28 coatings based on epoxy resin modified with liquid in the presence of phosphoric acid followed by treating with toluene diisocyanate and phenolic resin. Speciality coatings based on cardanol-formaldehyde resins copolymerized with toluene diisocyanate has been reported by Hu et a1 29. Processes for the development of high adhesion coatings, varnishes, sealing compounds and fire-resistant foam materials have also been developed 334. Polyurethanes containing unsaturated esters curable by radicals for use as sealing compounds for anchoring rods have been prepared from novolac-diphenylmethane diisocyanate and benzoyl peroxide 35. Interpenetrating polymer networks derived from soybean oil-based polyurethanes and cardanol-m-aminophenol dye has also been reported 36. Recently the synthesis and characterisation of polyurethanes based on cardanol-formaldehyde resins using dicyclohexyl methane diisocyanate (SMDI) has also been reported 37. However synthesis and characterisation of polyurethane sheets based on novolac resins and hydroxyalkylated cardanol -formaldehyde resins (synthesised polyols) with diphenylmethane diisocyanate and toluene diisocyanate have not been reported earlier. Hence, in the present investigation, a systematic synthesis and characterisation of hard and soft segment polyurethanes based on the cardanot-formaldehyde novolac resins and the synthesised polyols have been undertaken.

5 78 32 EXPERIMENTAL 32.1 Synthesis of polyurethanes based on novolac resins Polyurethanes were prepared using diphenylmethane diisocyanate and toluene diisocyanate. Novolac resins were vacuumdried before use. Dibutyltin dilaurate was used as catalyst. Commercial polyol, poly propylene glycol-2 (PPG-2) was dried in vacuum oyen. The chemicals used for the synthesis and their source are given in Table 3.1. Table 3.1 Chemicals used for polyurethane synthesis No Chemicals used Source 1. Di isocyanate: (I) Diphenylmethane diisocyanate (MDI) Fluka chernie AL (R) Toluene diisocyan.ate(tdi) Fluka. chemie AL UK 2. Polyol: polypropylene oxide glycol-2 Aldrich chemicals (PPG-2) USA 3. Catalyst: Dibutyltin dilaurate (DBTDL) Fluka chemie A.G. UK The mole ratios used in the preparation of polyurethanes based only on the novolac resin and the diisocyanate, diphenylmethane diisocyanate or toluene diisocyanate producing hard segment polyurethanes and also the polyurethanes based on novolac resin, the diisocyanate, diphenylmethane dilsocyanate or toluene diisocyanate and the commercial polyol, PPG-2 producing soft segment polyurethanes are presented in Table 3.2. In both the cases, the isocyanate index (NCO/OH mole ratio) is kept at 1.4.

6 79 The hard segment polyurethanes prepared from novolac resins using diphenylmethane dilsocyanate are denoted as "CRM" and the corresponding soft segment polyurethanes are denoted as "CRMP". The hard segment polyurethanes prepared from novolac resins using toluene diisocyanate are denoted as "CRT" and the corresponding soft segment polyurethanes are denoted as "CRTP". The hard segment polyurethanes prepared from synthesised polyol using diphenylmethane diisocyanate are denoted as "CREHM" and the corresponding soft segment polyurethane are denoted as "CREHMP". The hard segment polyurethanes prepared from synthesised polyol using toluene diisocyanate are denoted as "CREHT" and the corresponding soft segment polyurethanes are denoted as "CREHTP". Table 3.2 Formulation of polyurethanes based on novolac resin. Polyurethanes Diisocyanate Novolac resin PPG-2 Mole - Concentration (mole x functionality) Concentration Mole (mole x functionality) Concentration Mole (mole x functionality) CR1M CR2M CR3M CR1MP CR2MP CR3MP CR1T CR2T CR3T CR1TP CR2TP CR3TP

7 E-4111 Vacuum-dried novolac resin and vacuum-dried diisocyanate were added and mixed up in a cup at room temperature. It was then stirred with a glass rod gently. Dibutyltin ditaurate (.12 %) catalyst was then added and mixed gently. The mixture was left undisturbed for 1-15 min,for the air bubbles to settle. It now looked like a warm honey. Then it was transferred to the mould by pouring on the outer edge first and then inside. No upper or tower miniscus was left. It was then allowed to cure for 24 h without any disturbance. After 24 h, a razor blade was inserted on the outer periphery and the polyurethane sheet was removed gently from the mould. The percentage of hard segment was also calculated Synthesis of polyurethanes based on synthesised polyols The polyurethanes based on commercial polyol (PPG, 2), diphenytmethane diisocyanate or toluene diisocyanate, and synthesised polyots CR 1 EH, CR 2 EH, and CR 3 EH were also prepared as discussed in section The isocyanate index in all these cases was also kept at 1.4. The mole ratios of the reactants are presented in Table 3.3. The percentage of hard segment was also calculated.

8 81 Table 3.3 Formulation of polyurethanes based on polyols Diisocyanate Polyurethanes I Concentration Mole (mole x CR1EHM CR2EHM CR3EHM CR1EHMP CR2EHMP CR3EHMP CR1EHT CR 2 EHT CR3EHT CR1EHTP CR2EHTP CR3EHTP functionality) Synthesised polyols Concentration Mole (mole x functiortality).1 1. (1.1 G Commercial Polyol (PPG-2) Concentration Mole (mole x functionality) Spectral studies Infrared spectral analysis was carried out for polyurethanes by KBr pellet method using 3ASCO FT infrared spectrophotometer-41, Japan. Pure and dry samples were used for recording the spectrum Determination of frequency shift values The frequency shift, "&i" which has been measured as strength of hydrogen bqno is calculated using individual JR spectrum of polyurethane by using the expression, AV = 11 f + l)

9 82 where t-' = frequency of maximum absorption for the free -NH groups V b = frequency of maximum absorption for the hydrogen bonded -NH groups Determination of crosslink density and molecular weight between crosslinks The density of the polyurethanes was determined as per ASTM D 792. The crosslink density (y) of the polyurethane was determined from solubility parameter of the polyurethane. The solubility parameter was determined by conducting swelling experiments using small rectangular specimens in seven different solvents, starting from n-hexane to glycerol having solubility parameters 7.3 to 16.5 [(cal cm 3 ) 112 ] respectively (Table 3.4). The swelling coefficient 'Q' was calculated using the formula, Weight of solvent in swelled polymer x d Q= Weight of the polymer subjected to swelling x dr Where d 5 = density of solvent dr = density of polymer.

10 Table 3.4 Solubility parameters of solvents used for determination of solubility parameter of polyurethanes. 83 Solubility SLN. Solvent parameter [(cal CM 3)1/2] 1 Hexane Benzene Acetone Dimethyl acetamide Dimethyl formam[de Ethylene glycol Glycerol S 16.5 The crosslink density or effective number of moles of crosslinked unit per gram of polyurethane was determined using modified Flory Rehner equation, 38 y= Vr + X Vr2 + In (lvr) = drvü (Vr 1 " 3 - Vr12) M Where Vr Volume fraction of polyurethane in swollen polymer i.e V = 1/1+Q, where Q = swelling coefficient. X = Polymer - Solvent interaction parameter V = Molar volume of the solvent. M = Molecular weight between two crosslinks. dr = Density of the polyurethane.

11 IwIl Solvent absorptivity percentage Swelling behaviour of polyurethanes was also studied. Each polyurethane sheet was put in 3 ml of different solvents for 16 h. Excess of the solvent present on the surface of the polyurethane sheet was removed in folds of a filter paper. Then it was weighed and the solvent absorptivity percentage (SA %) was calculated using the following equation, (W2 - W1) SA% x Wi Where W 1 = Weight of the dry sample W2 = Weight of the sample after absorption of the solvent Thermal properties The thermal properties of the new polyurethanes were determined by Differential thermal analysis (DTA) and Thermo gravimetric analysis (TGA). For the thermal analysis, a Dupont 21 (USA), Shimatzu DT4 (Japan) and Mettler Toledo (Germany) thermal analyzers were used. The sample was heated in a DTA analyzer from ambient to 5 C at the heating rate of 1 OC/min under atmospheric condition. The appearance of peaks for glass transition temperature, softening temperature and decomposition temperature was checked for all the polyurethanes. - The thermogravimetric analyses (TGA) were carried out at the heating rate of 1 C/mm. The samples were heated from ambient to 1

12 85 8 C under nitrogen atmosphere. The weight loss was noted for all the polyurethanes Mechanical properties The tear strength of the polyurethanes was determined as per ASTM D using unnicked 9 angle test specimens which were punched out from cast sheets. A Zwick universal testing machine (1435 Model-Germany) was used. Indentation hardness (shore A) was determined as per ASTM D Polyurethane sheets were piled together to get a thickness of 5 mm and used for hardness measurement. A hardness tester (Durometer) was used. Tensile strength of polyurethane sheets was determined using dumb-bell specimens punched out from cast polyurethane sheets according to ASTM D The gauge length was fixed at 3 cm in each test. The chart speed and cross head speed were 1 mm/mm. The tensile strength and percentage elongation were calculated using standard formulations. An average value of six test data was calculated and presented. The average value lies within the standard deviation of 5%.

13 L.T [S1SI 3.3 RESULTS AND DISCUSSION Synthesis of polyurethanes The condensation reaction between novolac resins / synthesised polyols and dilsocyanate can lead to the formation of stable urethane linkages. The condensation reaction was found to be exothermic in both types of resins. The reaction was carried out in the presence of dibutyltin dilaurate catalyst and was completed within 15 mm. It was found earlier that in the presence of organo tin catalyst and the absence of water the reaction between the hydroxyl groups and isocyanate groups gives urethanes at temperature below 1 C Dusek43 proposed that the formation of urethane is the fastest reaction. Tin compounds with shorter alkyl groups have higher reactivity than those with longer groups. Diethyltin is the most effective catalyst, but due to toxicity considerations, alkyl groups shorter than butyl are rarely used commercially43. The mechanism of catalytic behaviour of dibutyltin dilaurate has been published already 44. The reaction rate depends on the reactivity of isocyanate groups and polyols. In the case of polypropylene glycol (PPG) one end has secondary hydroxyl group and the other end has primary hydroxyl group. The primary hydroxyl group is more reactive than the secondary hydroxyl group which makes the polypropylene glycol relatively lesser reactive than Polytetramethylene glycol (PTMG).

14 87 However difference in reactivity between PTMG and PPG polyol is less pronounced". Second order kinetics for the condensation between isocyanate and hydroxyl group has been suggested by some investigators4647. Pseudo first order kinetics was also suggested for the reaction of aliphatic isocyanate with excess alcohol 48. The most acceptable mechanism for the polyurethane formation has been proposed by Robin S49. The ratio of isocyanate hydroxyl group, (1.4:1) is chosen in the present synthesis of polyurethanes, so that excess of isocyanate present leads to the formation of terminal isocyanate groups which has been indicated by (Eq.13). (n+1)ocn-r-nhcoo OCO NH - R - NCO + n HO - R'-OH OCN (RNH COO OCONHRNHCOOR'OCONH) RNHCOO OCONHR - NCO (Eq. 13) The final curing of the reaction product leads to the formation of allophanate linkages with the reaction involving terminal isocyanate group with active hydrogen groups present in urethane groups of the polymer (Eq.14)

15 reini r.x. YY'RNHCO w'- OCO-NHR'-OCONH-R NCO GO1H -Rw\- wr-nhc 'w OCO-NH-R' - OCO-N-R -w- (Eq. 14) The branching and the crosslinking in the present polyurethane are possible due to the higher isocyanate index 1.4 and multifunctional hydroxyalkylated resins. The present polyurethanes are composed of variety of groups in the polymer chain including urethane, ether, allophanate, hydrocarbon, aromatic in addition to unreacted hydroxyl groups. Moreover the geometry and molecular weight of the hydroxyalkylated resin, polarity and molecular weight of the polyol are the other factors which could influence the ultimate properties of the polyurethanes Percentage of hard segments in the polyurethanes based on novolac resins/synthesised polyols The formulation of hard segment polyurethanes and the commercial polyol-added polyurethanes based on novolac resins are presented in Table 3.5.

16 Table 33 Percentage of hard segments in polyurethanes based on novolac resins. Polyurethane Hard Segment (%) CR 1 NI 1. CR 2 M 1. CR 3 M 1. CR I MP 71.4 CR2 MP 66.7 CR 3I4P 6. CR 1T 1. CR 2T 1.G CR 3T 1. CR 1TP 71.4 CR 2TP 66.7 CR 3TP 6. The hard segment content in CR 1 M, CR2 M, CR 3 M, CR 1T, CR2T and CR 3T is l%. Since these resins are multifunctional, they react with bifunctional toluene diisocyanate or diphenylmethane diisocyanate to give completely crosslinked structure with urethane and allophanate structures. The hard segment content for the polyurethanes prepared with the addition of commercial polyol is reduced and it ranges from 1hc. cu- 71% to 6% in the polyol-added polyurethanes. Si-rni1ar4s the +estdts in the case of synthesised polyols also (Table 3.6).

17 all Table 3.6 Percentage of hard segments in polyurethanes based on synthesised polyols urethane Hard Segment (%) R 1 EHM t 1. CR 2 EHM 1. CR 3 EHM 1. CR 1 EHMP 77.8 CR2 EHMP 7.6 CR 3 EHP4P 6. CR 1 EHT 1. CR2 EHT 1. CR 3 EHT 1. CR 1 EHTP 77.8 CR2 EHTP 7.6 CR 3 EHTP 6. I The formation of crosslinked product of hard segment polyurethanes clearly indicates the completion of condensation reaction leading to stable products. The addition of commercial polyol influences the properties of the final product Spectral studies Infrared spectral studies have been used in the present investigation mainly to investigate the degree of hydrogen bonding, which has greater influence on properties.

18 91 Infrared spectrum of the hard segment polyurethanes are presented in Fig The JR spectral assignment for the polyurethanes is presented in Table 3.7. Table 3.7 IR Spectral assignments of polyurethane Frequency of peak (cm') Assignment N-H Stretching (Free) -H Stretching N-H Stretching (Bonded of polyurethane) Aromatic C-H Stretching C-H Stretching of methylene or alkyl C= stretching (Free) in urethane C= stretching (bonded) in urethane N-H bending in urethane C--C ether linkage. The spectral data of the polyurethanes clearly indicates the disappearance of peak due to isocyanate group at 2265 cm'. Similarly no residual isocyanate was detected in any of the present polyurethanes. The Hydrogen bonding was found in all the polyurethanes as shown in Chart 3.1. The peak at 34 cm' indicates the presence of -H stretching which has been noticed for all the polyurethanes. The peak at cm' indicates free N-H stretching frequency and the peak at cm' indicates bonded N-H stretching frequency.

19 92 N H Urethane o- N R---'-- H Urethane -'''--R'---- N C R imv\ N - Allophanate _/V\A R O if C N---R!_/W\ H Urethane Chart 3.1 Hydrogen bonding in polyurethanes

20 95 or) go i; Wavenumber[cm-1 I Fig. 3.1 IR spectrum of CR1M IN 1o! /be4fll.1] Fig. 3.2 IR spectrum of CR2M

21 ico 1i] oil H I 6' Wavenwnbei[cinl] Fig. 3.3 IR spectrum of CR3M kp I I I I I I I ( Wwenumber[cm- 1] Fig. 3.4 IR spectrum of CR1T

22 too go 2 4 [ Wawnib(cm.1J 4 Fig. 3.5 IR spectrum of CR2T so rl, 4 b Wabfm.1J Fig. 3.6 IR spectrum of CR3T

23 1 8 %T 6 41 I Wamimbecm1J Fig. 3.7 IR spectrum of CR1EHM 11 1 %T 8 7 L Wanumbe41) Fig. 3.8 IR spectrum of CR2EHM

24 ' I I I I I WanumbcT(cm-1) Fig. 3.9 IR spectrum of CR3EHM ---.' H ji 2-1 tj L I ( Wavenumber[cm- 1] Fig. 31 IR spectrum of CR1EHT

25 RA Wamnnbefcm.1J Fig IR spectrum of CR2EHT IN 8 2L ON 3 low low 4 Fig IR spectrum of CR3EHT

26 Frequency shift values The frequency shift, "&.i" calculated from the individual IR spectrum of all polyurethanes is presented in Table 3.8. The frequency shift in the polyurethanes ranges from cm'. In the cases of diphenylmethane diisocyanate added soft segment polyurethanes, the frequency shift is 11 cm -1. But in the case of toluene diisocyanate added soft segment polyuretharies, the frequency shift ranges from cm' (Table 3.8). Table 38 Frequency shift values of polyurethanes based on - novolac resins and synthesised polyols. Polyurethanes Au CR 1 MP 11 CR 2 MP - 11 CR4P CR ITP 152 CR 2TP 14& CR 3TP CR 1 EHMP 11 CR2 CEHMP 11 CR 3 CEF-tt4P 11 CR I CEHTP 126 CR 2 CEHTP 132 CR3 CEHTP 138 The frequency shift values indicate that these polyurethanes are hydrogen bonded and crosslinked. The IR spectra of some representative PPG-2-added polyurethane are presented in Fig

27 Iwo 4 Wathfcni1] Fig IR spectrum of CR1MP 1 / Q1\ _ % 1 I 61 1 / ( \ I i / ' I (VI V1i I I I 1 (V 1 I j I I I Ii I I I I Il! I I I I I I/If I 1 I j /i IjJ Ii \/ I! I Wavenumberlern-11 Fig IR spectrum of CR1TP q

28 1-11 V-/-, P Vw El 79' I venumiicm1] 1 4 Fig. 315 IR spectrum of CR1EHMP IN nbc4n1j Fig IR spectrum of CR1EHTP

29 3.3.3 Crosslink density and molecular weight between cross links 94 The density of the polyurethane prepared with higher mole ratio of cardanol: formaldehyde is found to possess higher density in comparison with that of other resins having lesser mole ratio. The swelling coefficients of representative cases of polyurethanes CR 1 M, CR 1T, CR I MP and CR 1 TP in the seven solvent systems studied are presented in Table 3.9. Table 3.9 Swelling coefficient of CR1 M, CR 1T, CRIMP and CR1TP in different solvents Swelling coefficient "Q' I Polyurethane Hexane T ieflzacetonejbma DMflEthvie Glycerol glycol CR 1 M T 81 o CR1T.3 CRIMP.51 CR1TP L.96J _1..IIT.8.18 A graph between the soiubuty parameters of solvents in the x-axis and the swelling coefficient of 'Q' of the polyurethanes in the y-axis was plotted (Fig. 3.17). The peak of the curve gives the solubility parameter of polyurethane (Op). Among all the solvents used the solubility parameter of dimethyl acetamide (ös) was found to be the solubility parameter of polyurethanes as there was maximum swelling

30 e--cr1t j 1MH 1TP imp; 1. z..8 C) ) C C,).4.2, Solubility parameter of solvents (Cal/cm3)12 Fig Swelling coefficient curves of Polyurethanes

31 only in this solvent The polymer - solvent interaction parameter (X) is given by the equation, 95 X = 13 + (Vs/RT) (6s-6p)2 Where Vs = Molar volume of solvent R = Gas Constant Os = Solubility parameter of DMA Op = Solubility parameter of polyurethane T = Absolute temperature 13 = Lattice constant. When Os = Op, the polymer solvent interaction parameter (X) becomes equal to the lattice constant (13). Using solvent interaction parameter X, the crosslink density of the polyurethanes is determined. Crosslink density plays an important role in determining the properties of polyurethanes 5. With amorphous polymers, large increase of crosslink density increases the properties such as hardness, glass transition temperature and softening temperature 5. With crystalline polymers, small increase of crosslink density, changes the polymer from high melting, hard dense crystalline polymer to a more elastic, softer amorphous polymer. However with higher increase of crosslink density, the effect observed with amorphous polymer could be noticed in the crystalline polymers. The molecular weight between crosslinks (Me) indicates the degree of crosslinking. Higher the M, lower will be the crosslink density. The effective crosslink density of polyurethane is the

32 96 sum total of physical and chemical crosslinks. These crosslinked polymer will only swell in a non-reactive solvent and do not dissolve in a non-reactive solvent. The degree of swelling in a non-reactive solvent determines the degree of crosslinking and molecular weight between crosslinks. In the present investigation the polyurethanes prepared only from novolac resins/synthesised polyols are found to possess hard segments (1%). The crosslink density of these polyurethanes is found to be higher in comparison with that of the polyurethanes prepared with addition of commercial polyol, PPG-2 (Table 3.1). Accordingly the molecular weight between crosslinks, Mc is also found to be minimum in these cases. The percentage of hard segments in the commercial polyol-added polyurethanes ranges from The reduced percentage of hard segment resulted in the reduction of crosslink density in this class of polyurethanes. The low crosslink density of commercial polyol-added polyurethanes may also be due to the steric hindrance of the pendant methyl groups of Polypropylene glycol.

33 97 Table 3.1 Characterisation of networks of polyurethanes of novolac resins. Polyurethane CR1M CR2M CR 3 M CRIMP CR2MP CR3MP CR1T CR2T CR3T CR1TP CR2TP CR3TP Density (g/cc) Swelling coefficient in DMA(Q) Crosslink density (xlo3) Molecular weight between cross links (mole-') Polyurethanes prepared with hydroxyalkylated cardanolformaldehyde resins, (synthesised polyols) also exhibit a very similar behaviour as observed in the case of novolac resins (Table 3.11). However, the polyurethanes based on synthesised polyols show higher molecular weight between crosslinks. This is attributed to the variation in geometry, structure and number of hydroxyl groups present in the synthesised polyols. It is concluded that all the polyurethanes studied in the present investigation are crosslinked polymers.

34 I Table 3.11 Characterisation of Networks of polyurethanes of hydroxyalkylated Cardanol formaldehyde resins. Polyurethane I CREHM PCR2EHM LCR3EHM LC R 1 E H M P C R2 E H M P E H M P CR I EHT CR2 EHT CR3 EHT CR1EHTP CR2EHTP CR3EHTP Density (g / cc) Swelling coefficient in DMA(Q) Cross link density (xlo3) Molecular weight between cross links (mole') Solvent absorptivity percentage From the data of solvent absorptivity percentage (SA %) furnished in Table 3.12 and 3.13, the following inferences can be drawn. The solvent absorptivity percentage of all the polyurethanes prepared from novolac resins increases from the non-polar to polar solvents indicating the hydrophobic nature of these polyurethanes. Maximum swelling is noticed for all the polyurethanes in polar aprotic solvents like DMF and DMA.

35 I- a, U > C' cc c d a; CD I i- i-f I J N N Lfl loh We ko ko tc H I li-f I 1,-f U) U, a, I- U > 9-. U, a, C a,. 9- ) C, (U 4.' C a, U a,. 4-' >. U). 4-' C a, (I) a, C-.v >. -C - 'U U- a, C a, U i-i m a, I 'U E L. I.- L. U a, C a, N C a, co a, C a, x C. 4-I w 4- > U-) C^ (N (N rfl In ko kd In i-fl In (N (N (NM Cfl Cfl i-s i- Mr r' N RD rn H cc r lo H H o lo lo cc IN lo r cc " lo I Hs I cc O ON t D D N cc cc a Lfl In i-fl N a) o N cc cc i-s In In Ifi cc o o N N N - D D rl^ D a o N co rn i- cr c.fl.o cc cc O Lfl D M m m- - N In N N NJ l c^ - t 1 11) I r- In i-s O Ui ON D Ifi ¼ In cf N a) cc D N NO i-s N N (fl ffl Cn D 'D O (fl rn rn O 'D ¼ I o N o rn cc cc rnt o o rn cc o o N i- rj N cc o a N cc cc In In N N N I ^ I T-4 r-4 C^ ^ CL (N m A CL i CL IO. LO 1. t. rnj rsi i-f i-f (fl rn m rq I j Im CK 1 rj U U pu u U I JU lu u u u Pu

36 4-, > iu a r L1 L L a c ICO w I ii a) I Lu l kn L LU > 'c 'o N N rn - CO c C) C) -i N N N N ' '-I -I N N M I I N I I I C) CO o C) C) I I m CO C) N H I' '- I I l I L- 1 m '-I >1 '4- U) U) (U U) 4-, ) w I- D > a) I- 4-I CO a) C U - tu ),_ CL m U > CL 'I) (U 4,1 C ) > li a) C 4.' a) 1 z LU E ii a) C a) N C a) CO Ui O N O C CT C) N ( O' N LO 1, CO C) rn CO rn N N N N CO CO Ui Li '. N N CO rn C' N 'j N C' Lfl I N -4 O CON N N C") CO C) N M ' U') N m N N CO N N N (N i-i '. Lfl Li '. rn N '. N N CO N C") CO G C) '- N r*, ^ "^m ( Li Lfl LI) N N N LI') LI) LI) C) '. ( LI i-4 '. rfl CO H 4 N N C) -4 rn '. '. N '. r-, o - N N N rfl rn m'. '. '. (n(' ". Ic'. jc V1! h ri '. C'! C) - in '. C) (D 1,4.1 T (N rnr U') LI) LI) Cfl M. rn LI) Li LI) w CO ct- (N 't -4 C) N II- rn N rn - C) N Q C) '-1 CO i C) (N (N (N - i- ( r -i N (N Nnrn m I L C O_ i) i_ CA i F- r I I I I c II >. LU '- LU LU LU LU LU LU LU LU LU LU LU (N ( -4 (N (Ii -1 (N (') IN o o c c c cy. Q I a OIL) OIL) ulu u li

37 11 Diphenylmethane diisocyanate treated polyurethanes have higher SA% in all the solvents when compared to that of toluene diisocyanate treated polyurethanes indicating the more hydrophobicity in the former case than the latter. Similar solvent absorptivity percentage is also noticed in the case of polyurethanes prepared from synthesised polyols Thermal studies Crosslink density, molecular weight between crosslinks, percentage hard segment, percentage soft segment largely influence the thermal properties of the polyurethanes 51. Presence of long alkyl side chain at the meta position and the hard segment existing between urethane linkages largely influence the thermal properties of hard segment polyurethanes based on diphenylmethane diisocyanate or toluene diisocyanate. In the case of soft segment polyurethanes based on diphenylmethane dilsocyanate or toluene diisocyanate, apart from the above reasons, presence of flexible polyether polyol segment also accounts for the thermal behaviour Differential thermal analysis Differential thermal analysis of some diphenylmethane dilsocyanate or toluene dilsocyanate treated hard segment polyurethanes and the commercial polyol added soft segment polyurethanes of novolac resins are presented in Fig No endothermic peak has been noticed in all these polyurethanes (Table 3.13). However, both the hard and soft segment polyurethanes

38 so, 7 C S Ci 6 S a. 12 to C > Ba C. U BX to -e Deg C Fig TGA and DTA curves of CR1M OH U J U 2 - I -O To91joratu' (C) Fig TGA and DTA curves of CRIMP

39 P. - r. 8-1 o H 1 (3 -- C. : 13 : :)C boo Fig. 3.2 TGA and DTA curves of CR3MP Fig TGA and DTA curves of CR3T

40 / / 1 'I C Fig TGA and DTA curves of CR1TP

41 12 show two exotherms, a weak one around 3 C, and a strong one above 38 C, ranging from C. The weak exotherm is due to the cleavage of meta-substituted alkyl side chain in the phenyl ring. This is well in conformity with the results reported earlier Table 3.13 Differential Thermal Analysis Data of polyurethanes of Novolac resins Polyurethane First Exotherm ( C) Second CR1M CR2M CR3M 29 6 CR1M 3 4 CR2M CR3M CR1T CR2T CR3T 3 32 CR1TP 3 39 CR2TP CR3TP Highest exotherm 645 C is noticed in the case of diphenylmethane dilsocyanate treated hard segment polyurethane, CR 1 M. The corresponding soft segment polyurethane namely, CRiMP shows the second exotherm only at 4 C. In the case of toluene diisocyanate treated polyurethanes also, the second exotherm is found to be maximum in the hard segment case than the corresponding soft segment.

42 13 There is a gradual decrease in ithe second exotherm when we move from the higher mole ratio of cardanol : formaldehyde polyurethanes to that of lower mole ratio of cardanol : formaldehyde polyurethanes. The differential thermal analysis very clearly indicates the thermal stability of diphenylmethane dilsocyanate treated polyurethanes when compared to toluene dilsocyanate treated polyurethanes. In the case of synthesised hydroxyalkylated cardanolformaldehyde resins based polyurethanes with diphenylmethane diisocyanate or toluene diisocyanate (Fig ) also exhibit a similar behaviour. The commercial polyol treated polyurethanes also exhibit a very similar trend (Table 3.14). Table 3.14 Differential Thermal Analysis Data of Polyurethanes of synthesised polyols Polyurethane Exotherm ( C) First Second CR 1 EHM CR 2 EHM CR 3 EHM CR1EHMP CR 2 EHMP CR 3 EHMP CR1EHT CR 2 EHT CR 3 EHT CR 1 EHTP CR2 EHTP CR3 EHTP /

43 U Fig TGA and DTA curves of CR1EHM 1 5 9, I\ / 7 Cl , \\ Temperature ( C) Fig. 324 TGA and DTA curves of CR3EHM

44 tq -i ITB 1 go. ' B r B to B B 7 B > 7 EL - 6 U.4 4 x a go a I 4 3 -t P Fig TGA and DTA curves of CR1EHMP tool U.lJ 2 4-I C C, > L C, Temp erature ( C) Fig TGA and DTA curves of CR3EHMP

45 1 'S v ,-- 'S \ \ I 5.5 II n n-1 I I \ I I I. I I I I I I I I I I I mi n Fig TGA and DTA curves of CR1EHT 18 1 So - so, C. a a Dog C Fig TGA and DTA curves of CR3EHTP

46 14 In the hydroxyalkylated cardanol-formaldehyde resins also, diphenylmethane diisocyanate treated hard segment polyurethanes of higher mole ratio is exhibiting the highest second exotherm, indicating its maximum thermal stability Thermo gravimetric studies Thermograms of some representative polyurethanes are presented in Fig The data showing the percentage weight loss at various temperature ranges are furnished in Table 3.15 and Table Table 3.15 Thermo gravimetric analysis data of Polyurethanes of novolac resins In the case of polyurethanes prepared from cardanolformaldehyde novolac resins, thermal stability is found to be less when compared to that of polyurethanes based on phenol-formaldehyde resins 51. This may be attributed to the stereo chemical crowding of alkyl

47 Fig 3.29 TGA curve of CR3M IC 3? olog COO 'Co 2 XC lao 5 5 ICC 53 Fig. 3.3 TGA curve of CR1T

48 ' I w I 6 IC : I C1 4 i 2 U r------r DegC Fig TGA curve of CR3TP : Temperature ( C) Fig TGA curve of CR3EHT

49 Fig TGA curve of CR1EHTP

50 15 side chain at the meta position of the cardanol, which may decrease the case of crosslinking and also their higher thermal degrading aptitude as compared to benzene nucleus. Both the polyurethanes developed using cardanol-formaldehyde novolac resins and the hydroxyalkylated cardanol-formaldehyde resins (synthesised polyols) showed the following thermally induced phenomena: (i) A minor weight loss (v 2%) has been observed in the temperature range of -2 C, due to the moisture present in the sample. (ii) A gradual weight loss which occurs in the temperature range of 2-3 C, may be due to the re-crosslinking or post curing process. Re-crosslinking in these polyurethanes makes them more rigid. The new crosslinks formed in these polyurethanes develop a strain in the macro molecular chains. The small groups present outside the macro molecular structure are released with a weight loss of about 5%. (iii) 85% weight loss occurs in the temperature range 3-5C, which may be due to the segmental release of larger groups. (iv) Pre polymeric part has been left as the char residue in the temperature range of 5-6C. In the present investigation (Table 3.15), it has also been found that both the hard segment and soft segment polyurethanes derived from novolac resins and diphenylmethane diisocyanate are found to undergo no weight loss up to 1 C indicating the absence of moisture.

51 16 Even in the case of toluene dilsocyanate treated hard and soft segment polyurethanes, a very small weight loss (within 1%) has been noticed. In both the cases, hard segment polyurethanes are thermally stable than soft segment polyurethanes. Between the diphenylmethane dilsocyanate and toluene diisocyanate treated polyurethanes, the former ones are found to be thermally stable than the latter. In both the cases, the hard segment polyurethanes are thermally stable up to 65 C and the soft segment polyurethanes are thermally stable up to 5C. The percentage weight loss, even at higher temperature, in the case of higher mole ratio of cardanol formaldehyde hard segment polyurethanes are comparatively lower than that of lower mole ratio of cardanol : formaldehyde polyurethanes, indicating the higher stability of these polyurethanes. The same trend has been noticed in the case of soft segment polyurethanes also. In the case of polyurethanes prepared from synthesized polyols also (Table 3.16), a similar trend has been observed.

52 17 Table 3.16 Thermo gravimetric analysis data of Polyurethanes of synthesised polyols Polyurethane % Weight loss at various temperature C CR1 EHM CR2 EHM CR3 EHM CR1EHMP CR 2 EHMP CR3 EHMP CR1EHT CR 2 EHT CR 3 EHT CR 1 EHTP CR2 EHTP CR3 EHTP The thermal stability of diphenylmethane diisocyanate treated polyurethanes has been reflected in the mechanical properties also Mechanical properties The mechanical properties of the polyurethanes especially tensile strength and tear strength are largely influenced by the presence of aromatic groups, ether groups, long alkyl chain, dangling chains, branching and crosslinking and also degree of secondary bonding forces (Hydrogen bonding) Tear characters Tear test dataof the polyurethanes of the present investigation are presented in Table 3.17 and Table 3.18.

53 18 Table 3.17 Tear characters of polyurethanes of novolac resins Molecular weight Tear Elongation I Tear Polyurethane between strength Modulus (%) cross links (kn/m) (kn/m) (mole') CR1 M B B B CR2 M B B B CR3 M B B B CR I MP CR 2 MP CR 3 MP CR 1T B B B CR 2T B B B CR 3T B B B CR 1TP CR 2TP CR 3TP B = Brittle Both the hard segment polyurethanes prepared from diphenylmethane diisocyanate and toluene diisocyanate, crumbles during tear test indicating their brittleness. The poor tear characteristics in these polyurethanes may be attributed to the higher crosslink density. As the commercial polyol, PPG-2 is being added, the percentage elongation increases thereby indicating the increase in degree of flexibility in these polyurethanes.

54 Table 3.18 Tear properties of hydroxya!kylated cardanol formaldehyde Polyurethane CR1EHM CR2EHM CR3EHM CR1EHMP CR2EHMP CR3EHMP CR1EHT CR 2 EHT -- CR3EHT CR1EHTP CR2EHTP CR3 EHTP B = Brittle resins (synthesised polyols) Molecular weight between cross links (mole-") Tear strength (kn/m) B B B B B B Elongation (%) ] S. Tear Modulus (kn/m) B B B B B B Similar is the trend noticed in the case of hydroxyalkylated cardanol formaldehyde resins based polyurethanes. The present study reveals that diphenylmethane diisocyanate treated polyurethanes are mechanically stable than toluene diisocyanate treated polyurethanes.

55 Shore hardness Shore hardness of polymers is defined as the resistance offered by the polymeric material to the penetration of truncated cone (shore 'A'). The shore hardness of the polyurethanes of the present investigation is presented in Tables 3.19 and 3.2 respectively. Table 3.19 Hardness of polyurethanes of novolac resins Molecular weight Hard Polyurethane Hardness between cross segment Shore 'A' links (mole') CR 1 M CR 2 M CR3 M CR 1 MP CR2 MP CR3 MP CR 1T CR2T CR3T CR 1TP CR2TP CR 3TP In the present investigation the shore hardness of hard segment polyurethanes are found to be more than that of the soft segment polyurethanes. This may be attributed to the presence of hard segment percentage in these polyurethanes. The higher shore hardness in both the hard and soft segment polyurethanes of the higher mole

56 111 ratios supports the higher crosslink density and lower molecular weight between the crosslinks. Table 3.2 Hardness of polyurethanes of hydroxyalkylated cardanol formaldehyde resins (synthesised polyols) Molecular weight Hard Polyurethane Hardness between cross segment Shore 'A' links (mole') CR 1 EHM CR2 EHM CR3 EHM CR 1 EHMP CR 2 EHMP CR3 EHMP CR 1 EHT CR2 EHT CR3 EHT CR 1 EHTP CR 2 EHTP CR3EHTP Similar trend has also been noticed in the case of polyurethanes prepared from synthesised polyols (Table 3.2) Tensile properties The tensile properties of the polyurethanes based on novolac resins and hydroxyalkylated cardanol formaldehyde resins (synthesised polyols) are presented in Tables 3.21 and 3.22 respectively.

57 112 Table 3.21 Tensile properties of polyurethanes of novolac resins Molecular weight Tensile. Tensile strength Elongation Polyurethane between Modulus Oj cross links (MPa) (MPa) (mole-'-) CR 1 M B -B-- B CR 2 M B -. B B CR 3 M B B B CR 1 MP CR2MP CR3 MP CR 1T B -- B B CR 2T B B B CR3T B B B CR 1 TP CR2TP CR 3TP B = Brittle Table 3.25 Tensile properties of polyurethanes of hydroxyalkylated cardanol formaldehyde resins (polyols) Molecular Tensile Tensile weight Elongation Polyurethane between cross strength (%) Modulus (MPa) (MPa) links (mole-') CR 1 EHM B B CR 2 EHM B B B CR3 EHM B B B CR 1 EHMP CR2 EHMP CR3 EHMP CR 1 EHT B B B CR2 EHT B B - B CR3 EHT B -- B B CR 1 EHTP CR2 EHTP CR3EHTP } B = Brittle

58 113 The tensile strength of polyurethanes prepared from novolac resins varies from MPa to MPa. In the case of hard segment polyurethanes prepared from both diphenylmethane diisocyanate and toluene diisocyanate are found to be brittle. The tensile strength for diphenylmethane diisocyanate treated soft segment polyurethanes are found to be higher when compared to that of toluene diisocyanate treated soft segment polyurethanes. Tensile properties of the prepared polyurethanes very clearly support the higher crosslink density in these polyurethanes. Similar trend is also noticed in the case of polyurethanes prepared from synthesised polyols. Tensile stress-elongation curves of these polyurethanes are presented in Fig From the figure, it can be inferred that the polyurethanes changes from rigid to tough character.

59 14 4-1' C C) I , s-- _- --- CR1 MP -g-cr2mp - L CR3MP Elongation (%) Fig Tensile stress-elongation curves of MDI treated soft segment polyurethanes based on novolac resins (5 (n (8 U, C) U, C 6 C) I- 4 -R- CR2TP : Elongation (%) Fig Tensile stress-elongation curves of TDI treated soft segment polyurethanes based on novolac resins

60 --CR1EHMP 3 -D--CR2EHMP -á-cr3ehmp Elongation (%) Fig Tensile stress-elongation curves of MDI treated soft segment polyurethanes based on synthesised polyols U, U) U) C) 1 C) I U , Elongation (%) Fig Tensile stress-elongation curves of TDI treated soft segment polyurethanes based on synthesised polyols

61 CONCLUSION From the present study, it can be concluded that the hard segment polyurethanes synthesised from cardanol-formaldehyde novolac resins and hydroxyalkylated cardanol-formaldehyde resins (synthesised polyols) are found to possess higher thermal stability than the soft segment polyurethanes. Diphenylmethane diisocyanate treated polyurethanes in both the cases are found to be mechanically and thermally stable than the toluene diisocyanate treated polyurethanes. The performance character also reflects the good thermal and mechanical stability of diphenylmethane diisocyanate treated polyurethanes.

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