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Technical briefs
Reported to the World Polyurethane Congress, Amsterdam, by Frank Rossitto, Senior Development Chemist of Bayer Corp, USA, and Norbert Adam of Bayer AG, Germany, the study examines the effects of using HFC-24Sfa and pentanes in rigid polyisocyanate and polyurethane laminate panel formulations. It concludes that the physical properties of current alternative blowing agents are very different, and foam systems using them will require different levels of reformulation, depending on the properties desired in the end-use. Compressive strength, foam flow, tensile strength and adhesion were all improved when the agent HFC-24Sfa was used. But the k-factor and burn performance were negatively affected. With normal and cyclopentanes, k-factor and burn performance were also diminished, as expected, but adhesion, dimensional stability and compressive strength were improved. The study also gives an insight into the parameters necessary and the potential complications of processing PIR and PUR foam systems on lamination machinery
CO, foam blowing technology wins automotive approval Foams blown with carbon dloxide have a higher surface viscosity than conventional water-blown foams, giving a ‘cleaner’ finish which is more suitable for foam-in-fabric applications (such as moulded seating for passenger vehicles). Blowing with carbon dioxide is a significant advance in technology, because it uses physical processes rather than chemical reactions to reduce density. Using water blowing, ICI has so far reduced seat foam density from the typical 1990 level of 60kg/m” to around 32kg/m7 - but CO, blowing promises to reduce this by a further 25% without compromise of comfort or foam durability.
cQl997 Elscvicr Scicncc
But the use of the gas also produces a foam with a larger number of open cells, which tends to reduce stability. To counter this; ICI Polyurethanes has developed a new range of PU systems which ensure robust processing with CO, blowing. One of the first applications of carbon dioxide blowing technology for production of low density polyurethane foam automotive seating will be at Morocco-based h4aghreb Elastoplast. The company will use the ICI Polyurethanes technology to make a seat unit for the Fiat Uno, and subsequently to produce a new generation of seating for the forthcoming Fiat Palio world car.
TECHNICAL
BRIEFS
Improvements in thermal stabilization of PVC Aromatic hydrazides offer an improvement in thermal stabilization of rigid PVC, according to research at Cairo University, Egypt. The relatively low stability of PVC under heat and light has always been a problem, despite the enormous technical and economic importance of this material. The effect shows itself as auto catalvtic loss of hydrogen chloride, discolouration and corrosion phenomena, together with a change in mechanical properties and a change in molecular weight caused by chainscission or cross-linking. The cause is thought to lie in various defect sites in the polymer chain, such as branching, chloroallyl end-groups, oxygen-containing groups, groups and head-to-head structures. the steric order of the monomer units may also have some influence on degradation. Aromatic hydrazides and their derivatives exhibit excellent stabilizing efficiency both through replacement of the labile chlorine with a relatively more thermally-stable
9
November I997
Additives for Polymers
Effect of mixing two types of aromatic hydrazides with reference stabilizers on the discolouration of thermally-degraded rigid PVC (at 180°C for 80 minutes)
Molar ratio
Absorbance”
Hydrazide A/dibasic lead carbonate
Molar ratio
Absorbance”
Hydrazide A/Cd-Ba-Zn stearate
100/o
0.23
100/0
0.23
75125
0.13
75125
0.09
50150
0.27
50150
0.22
25175
0.34
25175
0.28
O/l 00
0.55
O/l 00
0.53
Hydrazide H/Dibasic lead carbonate
Hydrazide H/Cd-Ba-Zn stearate
100/o
0.15
loo/o
0.15
75125
0.11
75125
0.05
50150
0.24
50150
0.20
25175
0.31
25175
0.24
O/l 00
0.55
O/l 00
0.53
“Absorbance was measured at h,,, = 500 nm Source: Polymer Degradation and Stabiliv
hydrazide moiety, and through effective absorption of degradation products. aromatic
They can act effectively at lower concentrations than conventional stabilizers such as dibasic lead carbonate, cadmium-bariumzinc stearate and n-octyltin mercaptide. The types investigated lowered the degree of discolouration of the PVC, by disrupting the conjugated bond sequences formed on the polymer matrix. When blended with any of the commonly used stabilizers, certain types showed a remarkable improvement both in the Ts value and in lowering discolouration, reaching a maximum at a molar ratio of 3 : 1 hydrazide to reference stabilizer. The improvement may be attributed to the protection offered by the aromatic hydrazide stabilizers to the polymer against the deleterious effect of the by-products (mainly metal chlorides) accumulated during the reaction of the organometallic stabilizers with the polymer chains. This results from the ability of the hydrazide linkages to coordinate with these by-products to form stable complexes with potential stabilizing power. The work suggests that aromatic hydrazide derivatives can be used as thermal stabilizers
10
in PVC, either on their own or in conjunction with some existing organometallic compounds. Polymer Degra$ation (1997) pp 3 17-329
and Stability, Vol 56
EVENTS Conference will give an up-date on functional fillers Latest developments in functional fillers for thermoplastics and thermosets is the subject of a conference of the same name - the fifth in the annual international business development conferences by Inter-tech - to be held in San Diego, California, USA, from 8-10 December 1997. Over the past decade there has been an average 9% growth per year in use of fillers in plastics, forming a global business valued today at more than $23 billion. In the USA, some 40% of all resin by tonnage weight, is compounded and blended with fillers and; with increasing understanding of the hmction performed by fillers, growth in the industry is expected to continue.
0 1997 Elsevier Science
CO, foam blowing technology wins automotive approval Foams blown with carbon dloxide have a higher surface viscosity than conventional water-blown foams, giving a ‘cleaner’ finish which is more suitable for foam-in-fabric applications (such as moulded seating for passenger vehicles). Blowing with carbon dioxide is a significant advance in technology, because it uses physical processes rather than chemical reactions to reduce density. Using water blowing, ICI has so far reduced seat foam density from the typical 1990 level of 60kg/m” to around 32kg/m7 - but CO, blowing promises to reduce this by a further 25% without compromise of comfort or foam durability.
cQl997 Elscvicr Scicncc
But the use of the gas also produces a foam with a larger number of open cells, which tends to reduce stability. To counter this; ICI Polyurethanes has developed a new range of PU systems which ensure robust processing with CO, blowing. One of the first applications of carbon dioxide blowing technology for production of low density polyurethane foam automotive seating will be at Morocco-based h4aghreb Elastoplast. The company will use the ICI Polyurethanes technology to make a seat unit for the Fiat Uno, and subsequently to produce a new generation of seating for the forthcoming Fiat Palio world car.
TECHNICAL
BRIEFS
Improvements in thermal stabilization of PVC Aromatic hydrazides offer an improvement in thermal stabilization of rigid PVC, according to research at Cairo University, Egypt. The relatively low stability of PVC under heat and light has always been a problem, despite the enormous technical and economic importance of this material. The effect shows itself as auto catalvtic loss of hydrogen chloride, discolouration and corrosion phenomena, together with a change in mechanical properties and a change in molecular weight caused by chainscission or cross-linking. The cause is thought to lie in various defect sites in the polymer chain, such as branching, chloroallyl end-groups, oxygen-containing groups, groups and head-to-head structures. the steric order of the monomer units may also have some influence on degradation. Aromatic hydrazides and their derivatives exhibit excellent stabilizing efficiency both through replacement of the labile chlorine with a relatively more thermally-stable
9
November I997
Additives for Polymers
Effect of mixing two types of aromatic hydrazides with reference stabilizers on the discolouration of thermally-degraded rigid PVC (at 180°C for 80 minutes)
Molar ratio
Absorbance”
Hydrazide A/dibasic lead carbonate
Molar ratio
Absorbance”
Hydrazide A/Cd-Ba-Zn stearate
100/o
0.23
100/0
0.23
75125
0.13
75125
0.09
50150
0.27
50150
0.22
25175
0.34
25175
0.28
O/l 00
0.55
O/l 00
0.53
Hydrazide H/Dibasic lead carbonate
Hydrazide H/Cd-Ba-Zn stearate
100/o
0.15
loo/o
0.15
75125
0.11
75125
0.05
50150
0.24
50150
0.20
25175
0.31
25175
0.24
O/l 00
0.55
O/l 00
0.53
“Absorbance was measured at h,,, = 500 nm Source: Polymer Degradation and Stabiliv
hydrazide moiety, and through effective absorption of degradation products. aromatic
They can act effectively at lower concentrations than conventional stabilizers such as dibasic lead carbonate, cadmium-bariumzinc stearate and n-octyltin mercaptide. The types investigated lowered the degree of discolouration of the PVC, by disrupting the conjugated bond sequences formed on the polymer matrix. When blended with any of the commonly used stabilizers, certain types showed a remarkable improvement both in the Ts value and in lowering discolouration, reaching a maximum at a molar ratio of 3 : 1 hydrazide to reference stabilizer. The improvement may be attributed to the protection offered by the aromatic hydrazide stabilizers to the polymer against the deleterious effect of the by-products (mainly metal chlorides) accumulated during the reaction of the organometallic stabilizers with the polymer chains. This results from the ability of the hydrazide linkages to coordinate with these by-products to form stable complexes with potential stabilizing power. The work suggests that aromatic hydrazide derivatives can be used as thermal stabilizers
10
in PVC, either on their own or in conjunction with some existing organometallic compounds. Polymer Degra$ation (1997) pp 3 17-329
and Stability, Vol 56
EVENTS Conference will give an up-date on functional fillers Latest developments in functional fillers for thermoplastics and thermosets is the subject of a conference of the same name - the fifth in the annual international business development conferences by Inter-tech - to be held in San Diego, California, USA, from 8-10 December 1997. Over the past decade there has been an average 9% growth per year in use of fillers in plastics, forming a global business valued today at more than $23 billion. In the USA, some 40% of all resin by tonnage weight, is compounded and blended with fillers and; with increasing understanding of the hmction performed by fillers, growth in the industry is expected to continue.
0 1997 Elsevier Science