polyurethanes from novolac resins and polyols...

CHAPTER 3

POLYURETHANES FROM NOVOLAC RESINS AND

POLYOLS

75

3.1 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 phenol-

formaldehyde 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' 0 . Bisphenol-A (35) based

phenolic resin, with polyisocyanate in the presence of an amine was

used in inorganic mouldings 11-14

HOCOH--0- 1 _(:^_CH3

(35)

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 binders20'21.

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 750). Auto-oxidation polymerization of

Polyurethane films based on cardanol, glycol and toluene diisocyanate

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 3034 . 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.

78

32 EXPERIMENTAL

32.1 Synthesis of polyurethanes based on novolac resins

Polyurethanes were prepared using diphenylmethane

diisocyanate and toluene diisocyanate. Novolac resins were vacuum-

dried before use. Dibutyltin dilaurate was used as catalyst. Commercial

polyol, poly propylene glycol-2000 (PPG-2000) 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-2000 Aldrich chemicals(PPG-2000) 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-2000 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.

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

CR1M

CR2M

CR3M

CR1MP

CR2MP

CR3MP

CR1T

CR2T

CR3T

CR1TP

CR2TP

CR3TP

Diisocyanate

- Concentration(mole xfunctionality)

- 0.70

- 0.56

- 0.42

- 0.98

- 0.84

- 0.70

- 0.70

- 0.56

- 0.42

- 0.98

- 0.84

- 0.70

Novolac resin

ConcentrationMole (mole x

functionality)

0.1 0.5

0.1 0.4

0.1 0.3

0.1 0.5

0.1 0.4

0.1 0.3

0.1 0.5

0.1 0.4

0.1 0.3

0.1 0.5

0.1 0.4

0.1 0.3

PPG-2000

ConcentrationMole (mole x

functionality)

0.0 0.0

0.0 0.0

0.0 0.0

0.1 0.2

0.1 0.2

0.1 0.2

0.0 0.0

0.0 0.0

0.0 0.0

0.1 0.2

0.1 0.2

0.1 0.2

Mole

0.35

0.28

0.21

0.49

0.42

0.35

0.35

0.28

0.21

0.49

0.42

0.35

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 (0.12 %) catalyst was

then added and mixed gently. The mixture was left undisturbed for

10-15 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.

3.2.2 Synthesis of polyurethanes based on synthesised polyols

The polyurethanes based on commercial polyol (PPG, 2000),

diphenytmethane diisocyanate or toluene diisocyanate, and synthesised

polyots CR 1 EH, CR2 EH, and CR3 EH were also prepared as discussed in

section 3.2.1. 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.

Polyurethanes IDiisocyanate

CR1EHM

CR2EHM

CR3EHM

CR1EHMP

CR2EHMP

CR3EHMP

CR1EHT

CR 2 EHT

CR3EHT

CR1EHTP

CR2EHTP

CR3EHTP

Concentration

(mole x

functionality)

1.400

1.120

0.840

1.260

0.952

0. 588

1.400

1.120

0.840

1.260

0.952

0.588

Mole

0.700

0.560

0.420

0.680

0.476

0.294

0.700

0.560

0.420

0.680

0.476

0.294

Table 3.3

Formulation of polyurethanes based on polyols

81

Synthesised polyols

Concentration

Mole (mole x

functiortality)

0.10 1.00

(1.10 G80

0.10 0.60

0.07 0.70

0.06 0.48

0.05 0.30

0.10 1.00

0.10 0.80

0.10 0.60

0.07 0.70

0.06 0.48

0.05 0.30

Commercial Polyol(PPG-2000)

Concentration

Mole (mole x

functionality)

0.0 0.0

0.0 0-0

0.0 0.0

0.1 0.2

0.1 0.2

0.1 0.2

0.0 0.0

0.0 0.0

0.0 0.0

0.1 0.2

0.1

0.2

0.1

0.2

3.2.3 Spectral studies

Infrared spectral analysis was carried out for polyurethanes by

KBr pellet method using 3ASCO FT infrared spectrophotometer-410,

Japan. Pure and dry samples were used for recording the spectrum.

32.3.1 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)

82

where t-' = frequency of maximum absorption for the

free -NH groups

V b = frequency of maximum absorption for the

hydrogen bonded -NH groups.

32.4 Determination of crosslink density and molecular weightbetween 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 dQ= ------------------------------------------------------------

Weight of the polymer subjected to swelling x dr

Where d 5 = density of solvent

dr = density of polymer.

83

Table 3.4

Solubility parameters of solvents used for determination of

solubility parameter of polyurethanes.

SolubilitySLN0. Solvent parameter

[(cal CM 3)1/2]

1 Hexane 7.3

2 Benzene 9.2

3 Acetone 9.9

4 Dimethyl acetamide 10.85 Dimethyl formam[de 12.1

6 Ethylene glycol 14.6

- 7 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

Vr + X Vr2 + In (lVr)y= -- -----------------------------=

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

V0 = Molar volume of the solvent.

M = Molecular weight between two crosslinks.

dr = Density of the polyurethane.

IwIl

3.2.5 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 10

Wi

Where W 1 = Weight of the dry sample

W 2 = Weight of the sample after absorption of the solvent.

3.2.6 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 2100

(USA), Shimatzu DT40 (Japan) and Mettler Toledo (Germany) thermal

analyzers were used. The sample was heated in a DTA analyzer from

ambient to 500°C at the heating rate of 10 O C/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 10°C/mm. The samples were heated from ambient to

85

800 0 C under nitrogen atmosphere. The weight loss was noted for all the

polyurethanes.

3.2.7 Mechanical properties

The tear strength of the polyurethanes was determined as per

ASTM D 624-86 using unnicked 90 0 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 2240-86. 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 412-87. The gauge length was fixed at 3 cm in each test. The

chart speed and cross head speed were 100 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%.

L.T[S1SI

3.3 RESULTS AND DISCUSSION

3.3.1 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 100°C 3942 . 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).

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)

YY'RNHC0O w'- OCO-NHR'-OCONH-R NCO

GO1H -Rw\-

wR-NHC00 '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 hydroxy-

alkylated resin, polarity and molecular weight of the polyol are the other

factors which could influence the ultimate properties of the

polyurethanes.

3.31.1 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.

r.x.reINI

Table 33

Percentage of hard segments in polyurethanes

based on novolac resins.

Polyurethane Hard Segment (%)CR 1 NI 100.0CR 2 M 100.0

CR3 M 100.0

CR I MP 71.4

CR2 MP 66.7

CR3I4P 60.0

CR 1 T 100.0

CR 2T 100.G

CR 3T 100.0

CR 1 TP 71.4

CR2TP 66.7

CR3TP 60.0

The hard segment content in CR 1 M, CR2 M, CR3 M, CR 1T, CR2T

and CR3T is l00%. 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 from1hc. cu-

71% to 60% in the polyol-added polyurethanes. Si-rni1ar4s the +estdts in

the case of synthesised polyols also (Table 3.6).

all

Table 3.6

Percentage of hard segments in polyurethanes

based on synthesised polyols

t

urethane Hard Segment (%)R 1 EHM 100.0

CR 2 EHM 100.0

CR3 EHM 100.0

CR 1 EHMP 77.8

CR2 EHMP 70.6

CR3 EHP4P 60.0

CR 1 EHT 100.0

CR2 EHT 100.0

CR3 EHT 100.0

CR 1 EHTP 77.8

CR2 EHTP 70.6

CR3 EHTP 60.0I

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.

3.3.2 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.

91

Infrared spectrum of the hard segment polyurethanes are

presented in Fig. 3.1 - 3.12. 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')

3420-344534003315-33352955-30252855-29051720-17351635-165015401020-1110

AssignmentN-H Stretching (Free)0-H StretchingN-H Stretching (Bonded of polyurethane)Aromatic C-H StretchingC-H Stretching of methylene or alkylC=0 stretching (Free) in urethaneC=0 stretching (bonded) in urethaneN-H bending in urethaneC-0-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 3400 cm' indicates the presence of 0-H

stretching which has been noticed for all the polyurethanes. The peak at

3425-3445 cm' indicates free N-H stretching frequency and the peak at

3315-3335 cm' indicates bonded N-H stretching frequency.

92

N

H Urethane

o- N —R---'--

HUrethane

-'''--R'---- N

0C

_/V\A R—O

R iMv\

N -

Allophanate

ifC—N---R!_/W\

HUrethane

Chart 3.1 Hydrogen bonding in polyurethanes

95

or)

go

4000 3000 2000 1000 4i;

Wavenumber[cm-1 I

Fig. 3.1 IR spectrum of CR1M

IN

1o!

35 3000 2000 1000 400

/be4fll.1]


ico

1i]

oil H60'

I

4000 3000 2000 1000 400

Wavenwnbei[cinl]


100

80

60

kP

40

20

0 11 I I I I I I I

4000 3000 2000 1000 40(

Wwenumber[cm- 1]

Fig. 3.4 IR spectrum of CR1T

too

go

204000

[71000 4003000 2000

Wawnib(cm.1J


so

rl,

40

b

4000

3000 2800

1000 400

Wabfm.1J


100

%T

1

80

%T

60

401 I

4000 3000 2000 1000 400

Wamimbecm1J

Fig. 3.7 IR spectrum of CR1EHM

110

80

70 L-

4000

3000 1000 1000 400

Wanumbe41)


80

60

100

'

40 I I I I

4000 3000 2000 1000 400

WanumbcT(cm-1)


100----.-

---.'

80-

60H

jI

20-1

tj

L

0 ---------------- I

I 4000 3000

2000 1000 40(

Wavenumber[cm- 1]

Fig. 310 IR spectrum of CR1EHT

20

10

4000

RA

80

60

40

3000

2000 1000 400

Wamnnbefcm.1J

Fig. 3.11 IR spectrum of CR2EHT

IN

80

20L

ON

3000 low low 40

Fig. 3.12 IR spectrum of CR3EHT

93

3.3.2.1 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 110-152 cm'. In the cases of

diphenylmethane diisocyanate added soft segment polyurethanes, the

frequency shift is 110 cm -1 . But in the case of toluene diisocyanate

added soft segment polyuretharies, the frequency shift ranges from

126-138 cm' (Table 3.8).

Table 38

Frequency shift values of polyurethanes based on

novolac resins and synthesised polyols.

-Polyurethanes Au

CR 1 MP 110CR2 MP - 110CR4P -- 110CR ITP 152CR2TP 14&CR 3TP 148 -CR1 0EHMP 110CR2 CEHMP 110CR 3 CEF-tt4P 110CR I CEHTP 126CR2 CEHTP 132CR3 CEHTP 138

The frequency shift values indicate that these

polyurethanes are hydrogen bonded and crosslinked. The IR spectra of

some representative PPG-2000-added polyurethane are presented in

Fig. 3.13 - 3.16.

170

150

50

390 3000 2800 Iwo 400

Wathfcni1]

Fig. 3.13 IR spectrum of CR1MP

100

/

Q1\ 0%

_

1

/i

I j

601 1 / (

\ I i

/ ' I (VI V1i

0 I I I01 1 I

(Vj

IjJ

I I I IiI I I I Il!

I I I II I/If I 1I 1111 1

20 1

\/ I! I

Iiq

0.. ...__.

4000 3000 2000 1000 400

Wavenumberlern-11

Fig. 3.14 IR spectrum of CR1TP

200079' I

4000 3000 1000 400

IN

100

Vw

-11 V-/-,—

P

El

venumiIcm1]

Fig. 315 IR spectrum of CR1EHMP

4 300 0 20 1

nbc4n1J

Fig. 3.16 IR spectrum of CR1EHTP

94

3.3.3 Crosslink density and molecular weight between crosslinks

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 1 T, CR I MP and CR 1TP in the seven solvent

systems studied are presented in Table 3.9.

Table 3.9

Swelling coefficient of CR 1 M, CR 1T, CRIMP and CR1TP

in different solvents

Swelling coefficient "Q'I Polyurethane Hexane T

ieflZAcetoneJbMA DMflEthvie Glycerolglycol

CR 1 M 0.34. 0.48 073 1.16 T 81o. 0.24 0.10

0.40 0.63 1.14 1 0.64 0.17

9L0.96J1.21.07 0.42

0.65 0.82 1.19 0.92 0.36_1..IIT

CR1T

0.30

CRIMP 0.51

CR1TP 0.43

0.08

0.18

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

1.2

1.

z

. 0.8

C)000)C

C,)

0.4

0.2

j -e--CR1T

1MH

1TP

iMP;

1.4 -.-.--.-.-- ...-

0,

6

8 10 12 14 16 18

Solubility parameter of solvents (Cal/cm3)12

Fig. 3.17 Swelling coefficient curves of Polyurethanes

95

only in this solvent The polymer - solvent interaction parameter (X) is

given by the equation,

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 50 . With amorphous polymers, large increase

of crosslink density increases the properties such as hardness, glass

transition temperature and softening temperature 50 . 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

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 (100%). 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-2000 (Table 3.10).

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 71.4 - 60. 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.

97

Table 3.10

Characterisation of networks of polyurethanes of novolac resins.

Polyurethane

CR1M

CR2M

CR3 M

CRIMP

CR2MP

CR3MP

CR1T

CR2T

CR3T

CR1TP

CR2TP

CR3TP

Density(g/cc)

1.13

1.11

1.09

1.11

1.08

1.05

1.14

1.13

1.11

1.12

1.10

1.07

Swellingcoefficientin DMA(Q)

1.16

1.19

1.23

1.22

1.24

1.28

1.14

1.18

1.20

1.19

1.22

1.24

Crosslinkdensity(xlO3)

1.5052

1.4742

1.4328

1.4304

1.4262

1.4112

1.5440

1.4776

1.4532

1.4668

1.4434

1.4379

Molecularweight

between crosslinks (mole-')

664.36

678.33

697.91

699.08

701.16

708.62

647.67

676.77

688.14

681.76

692.81

695.46

Polyurethanes prepared with hydroxyalkylated cardanol-

formaldehyde 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.

I

Table 3.11

Characterisation of Networks of polyurethanes of

hydroxyalkylated Cardanol formaldehyde resins.

Density(g / cc)

1.16

1.14

1.12

1.12

1.11

1.10

1.17

1.15

1.13

1.15

1.13

1.11

Cross linkdensity(xlO3)

1.3178

1.2587

1.2076

1.2076

1.0919

0.9973

1.3537

1.2868

1. 23 18

1.2119

1.1313

1.0919

Molecularweight

betweencross links(mole')758.84

794.47

828.09

828.09

915.83

1002.70

738.72

777.12

811.82 -

825.15

883.74

915.83

Polyurethane

I CREHM

PCR2EHM

LCR3EHM

LC R 1 E H M P

C R2C E H M P

E H M P

CR I EHT

CR2 EHT

CR3 EHT

CR1EHTP

CR2EHTP

CR3EHTP

Swellingcoefficient in

DMA(Q)

1.25

1.30

1.35

1.35

1.44

1.53

1.22

1.27

1.32

1.32

1.39

1.44

3.3.4 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.

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101

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.

3.3.5 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.

3.3.5.1 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.3.18-3.22. No

endothermic peak has been noticed in all these polyurethanes

(Table 3.13). However, both the hard and soft segment polyurethanes

18

14

12

CtO

0>

BaC.U

BX

100

90

so

, 70CSCi 60

Sa.

40

30

20

to

0

2

0

-e

80

60 -

40 -J

20

Deg C

Fig. 3.18 TGA and DTA curves of CR1M

---- --- -------------OH

100..

U

0.4

U

0-O

- I

-.--- ..- --0.

200 400 600 800

To91joratu'0 (C)

Fig. 3.19 TGA and DTA curves of CRIMP

04---0

r.

C

:00 00 130 :00 :)0C bOO

P.0

00 -

80-1

•1

(30 --

.0

Fig. 3.20 TGA and DTA curves of CR3MP

Fig. 3.21 TGA and DTA curves of CR3T

o H

//

1

'I100 200 300 400 5C0 600 700

0 0 40 50 60 70

Fig. 3.22 TGA and DTA curves of CR1TP

102

show two exotherms, a weak one around 300 0 C, and a strong one above

380 0C, ranging from 380-645 0C. 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 51-53

Table 3.13

Differential Thermal Analysis Data of

polyurethanes of Novolac resins

Polyurethane Exotherm (°C)

First

Second

CR1M

301

645CR2M

295

630CR3M

290

600CR1M

300

400CR2M

280

390CR3M

275

380CR1T

315

330CR2T

310

325CR3T

300

320CR1TP

300

390CR2TP

295

393CR3TP

285

380

Highest exotherm 645 0C 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 400 0C. 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.

103

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 cardanol-

formaldehyde resins based polyurethanes with diphenylmethane

diisocyanate or toluene diisocyanate (Fig. 3.23-3.28) 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 377 616CR 2 EHM 350 540CR3 EHM 329 453CR1EHMP 303 366CR2 EHMP -- 350 390CR3 EHMP 280 380CR1EHT 295 395CR2 EHT 290 390CR3 EHT 280 385CR 1 EHTP 370 416CR2 EHTP - 360 410CR3EHTP 350 - 407

/

U

100

90

80

70

60

50

40

30-

20

10

00

Fig. 3.23 TGA and DTA curves of CR1EHM

05

0,15-1

Cl

I\ /7

-005

, \\

0 0100 200 300 400 500 600

Temperature (°C)

Fig. 324 TGA and DTA curves of CR3EHM

tQ -iITB

toB

B

7B

0>

U.4

4 x

a

a

I

0

-t

100

go.

' B0rB

70•EL -

60

go

40

30

100 200 300 400 500Temp erature (°C)

6

-2

210

too l--

.lJ

0

4

U0

4-IC

2C,

>

LC,

0

P00

Fig. 3.25 TGA and DTA curves of CR1EHMP

Fig. 3.26 TGA and DTA curves of CR3EHMP

18

£8

£4

1243

10

4

2

0

—a

- ----- ------- ----- -- -----.-- -v------,--

'S\

1 'S

\ I

5 0.5 II

n n-1 I I

\1

100 200 300 403 500 600 700

I I I . I I I I I I II I I I0 10 20 30 40 50 60 70 mi n

Fig. 3.27 TGA and DTA curves of CR1EHT

0

100

So -

so

, 70

80 60C.0a. 80•

30-

20-

£0 -

0-

Dog C

Fig. 3.28 TGA and DTA curves of CR3EHTP

104

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.

3.3.5.2 Thermo gravimetric studies

Thermograms of some representative polyurethanes are

presented in Fig.3.29-3.33. The data showing the percentage weight

loss at various temperature ranges are furnished in Table 3.15 and

Table 3.16.

Table 3.15

Thermo gravimetric analysis data of

Polyurethanes of novolac resins

In the case of polyurethanes prepared from cardanol-

formaldehyde novolac resins, thermal stability is found to be less when

compared to that of polyurethanes based on phenol-formaldehyde

resins51 . This may be attributed to the stereo chemical crowding of alkyl

Fig 3.29 TGA curve of CR3M

-- - -- --------.-------

00

70

IC

30

?0

olog

COO 'Co 200 XC lao 500 500 ICC 000 0053

Fig. 3.30 TGA curve of CR1T

120 --. •--.--- .--..-.-----

100

80-2' I

wI 60IC:0 I

C1 40

i 20

U r------r-

0 50 100 150 200 250 300 350 400 450

DegC

Fig. 3.31 TGA curve of CR3TP

120

100

801

60

401

2:1

100 200 300 400 500 600

Temperature (°C)

Fig. 3.32 TGA curve of CR3EHT

Fig. 3.33 TGA curve of CR1EHTP

105

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 0-200 0C, due to the moisture present in the sample.

(ii) A gradual weight loss which occurs in the temperature range of

2000 -3000C, 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 50%.

(iii) 85% weight loss occurs in the temperature range 3000-5000C,

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 5000-6000C.

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 1000C indicating the absence of moisture.

106

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 650 0C and the soft segment

polyurethanes are thermally stable up to 5000C.

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.

107

Table 3.16

Thermo gravimetric analysis data of

Polyurethanes of synthesised polyols

Polyurethane % Weight loss at various temperature °C

100 200 300 400 500

CR 1 EHM 1.0 5.5 16.0 47.0 63.0CR2 EHM 1.0 6.0 21.0 52.0 72.0CR3 EHM 1.0 6.0 25.5 55.0 78.5CR1EHMP 0 0 1.0 57.3 CR2 EHMP 0 0 2.0 60.0 CR3 EHMP 0.4 2.1 19.0 61.5 CR1EHT 0 1.7 15.0 51.0 77.0CR2 EHT 0 1.8 16.0 54.0 78.5CR3 EHT 0 2.0 21.0 60.0 80.0CR 1 EHTP 1.0 3.0 106 57.5 87.0CR2 EHTP 1.0 2.0 11.8 64.8 87.8CR3 EHTP 1.0 2.0 13.1 78.8 88.8

The thermal stability of diphenylmethane diisocyanate treated

polyurethanes has been reflected in the mechanical properties also.

3.3.6 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)50.

3.3.6.1 Tear characters

Tear test dataof the polyurethanes of the present investigation

are presented in Table 3.17 and Table 3.18.

108

Table 3.17

Tear characters of polyurethanes of novolac resins

Molecularweight Tear Elongation I Tear

Polyurethane between strength (%) Moduluscross links (kN/m) (kN/m)(mole')

CR 1 M 664.36 B B BCR2 M 678.33 - B B BCR3 M 697.91 B B BCRI MP 699.08 120.0 75.0 160.0CR2 MP 701.16 115.0 82.0 140.2CR3 MP 708.62 110.0 85.0 129.4CR 1 T 647.67 B B BCR2T 676.77 B B BCR3T 688.14 B B BCR 1 TP 681.76 70.0 70.0 100.0CR2TP 692.81 65.0 75.0 86.7CR3TP 695.46 60.0 80.0 75.0

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-2000 is being added, the percentage

elongation increases thereby indicating the increase in degree of

flexibility in these polyurethanes.

Tearstrength(kN/m)

BBB

115.0112.0100.0

BBB

95.090.085.0

Elongation(%)

111111]

S.

TearModulus(kN/m)

BBB

127.8112.0

90.9BBB

111.8100.089.5

109

Table 3.18

Tear properties of hydroxya!kylated cardanol formaldehyde

resins (synthesised polyols)

Polyurethane

CR1EHMCR2EHMCR3EHMCR1EHMPCR2EHMPCR3EHMPCR1EHTCR2 EHT --CR3EHTCR1EHTPCR2EHTPCR3 EHTP

B = Brittle

Molecularweight

betweencross links

(mole-")758.84 -794.47828.09828.09

- 915.831002.70738.72777.12811.82825.15883.74 -915.83

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.

110

3.3.6.2 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 3.20 respectively.

Table 3.19

Hardness of polyurethanes of novolac resins

Hard Molecular weight HardnessPolyurethane between crossShore 'A'segment

links (mole')CR 1 M 100 664.36 88

CR2 M 100 678.33 85CR3 M 100 697.91 80

CR 1 MP 71.4 699.08 65CR2 MP 66.7 701.16 60CR3 MP 60.0 708.62 55CR 1T 100 647.67 89CR2T 100 676.77 85CR3T 100 688.14 80CR 1TP 71.4 681.76 60

CR2TP 66.7 692.81 55

CR3TP 60.0 695.46 50

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

111

ratios supports the higher crosslink density and lower molecular weight

between the crosslinks.

Table 3.20

Hardness of polyurethanes of hydroxyalkylated cardanol

formaldehyde resins (synthesised polyols)

Hard Molecular weight HardnessPolyurethane between crossShore 'A'segment

links (mole')CR 1 EHM 100 758.84 97

CR2 EHM 100 794.47 96

CR3 EHM 100 - 828.09 92

CR 1 EHMP 77.8 828.09 67

CR2 EHMP 70.6 915.83 62

CR3 EHMP 60.0 1002.70 53

CR 1 EHT 100 738.72 97

CR2 EHT 100 777.12 95CR3 EHT 100 811.82 93

CR 1 EHTP 77.8 825.15 65

CR2 EHTP 70.6 883.74 60CR3EHTP 60.0 915.83 55

Similar trend has also been noticed in the case of polyurethanes

prepared from synthesised polyols (Table 3.20).

3.3.6.3 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.

112

Table 3.21

Tensile properties of polyurethanes of novolac resins

Molecular

weight Tensile . TensilePolyurethane between strength Elongation

Oj Moduluscross links (MPa) (MPa)

(mole-'-)CR 1 M 664.36 - B -B-- BCR2 M 678.33 B -. B BCR3M 697.91 B B BCR 1 MP 699.08 -21.47 120 17.89CR2MP- 701.16 19.16 128 14.97CR3 MP - 708.62 18.43 135 13.65CR 1T 647.67 B -- B BCR2T 676.77 B B BCR3T 688.14 B B BCR 1 TP 681.76 20.46 - 110 18.60CR2TP 692.811 18.52 117 15.43CR3TP 695.46 17.21 - 125 13.77B = Brittle

Table 3.25

Tensile properties of polyurethanes of hydroxyalkylated cardanol

formaldehyde resins (polyols)

Molecular Tensile Tensile

weight Elongation ModulusPolyurethane between cross strength (%)links (mole-')

(MPa) (MPa)

CR1 EHM 758.84 B BCR2 EHM 794.47 B B BCR3 EHM 828.09 B B BCR 1 EHMP 828.09 28.82 150 19.21CR2 EHMP 915.83 26.64 - 155 17.19CR3 EHMP 1002.70 24.49 163 15.02CR 1 EHT 738.72 B B BCR2 EHT 777.12 B B - BCR3 EHT 811.82 B -- B BCR 1 EHTP 825.15 25.67 140 18.34CR2 EHTP 883.74 24.34 145 16.79CR3EHTP 915.83 } 23.18 150 15.45

B = Brittle

113

The tensile strength of polyurethanes prepared from novolac

resins varies from 17.21 MPa to 21.47 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. 3.34-3.37. From the figure, it

can be inferred that the polyurethanes changes from rigid to tough

character.

16 -

14

12

(50

(n(8

U,C)

U,C 6C)I-

14 4

- 1' -

0

10

8

CC)I-6

4

2

0

—

-- - ---- -----

,- - ------

- —s-- _---

--- CR1 MP-g-CR2MP

- L CR3MP

10 20 30 40 50 60 70 80 90 100 110 120 130 140

Elongation (%)

Fig. 3.34 Tensile stress-elongation curves of MDI treated softsegment polyurethanes based on novolac resins

4

-R- CR2TP

:..____0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Elongation (%)

Fig. 3.35 Tensile stress-elongation curves of TDI treated softsegment polyurethanes based on novolac resins

--CR1EHMP

3 -D--CR2EHMP

-á-CR3EHMP

0 - - -0 20 40 60 80 100 120 140 160 180

Elongation (%)

Fig. 3.36 Tensile stress-elongation curves of MDI treated softsegment polyurethanes based on synthesised polyols

20

18

16

14

05 12U,U)

10U)

C)

C)I-

6

4

2

U ------,- -------.-0 20 40 60 80 100 120 140

Elongation (%)

Fig. 3.37 Tensile stress-elongation curves of TDI treated softsegment polyurethanes based on synthesised polyols

114

3.4 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.

115

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