ENGAGE™Polyolefin Elastomers Halogen Free Flame Retardant Cable Formulations
Introduction
Cable manufacturers must evaluate a range of properties when lecting a product as an insulating or cable sheathing material; properties such as electrical performance, mechanical properties including tensile and flexural behavior and, of cour, the overall system cost. Another key parameter in the lection process is the fire safety of the cable – particularly the flame retardancy of the insulation/jacketing material.
A protective layer made up of aluminium
oxide or magnesium oxide and the products四年级英语小故事
of carbonisation forms on the surface of the
plastic further hindering combustion. This
protective layer may also reduce smoke
density by absorbing soot particles.
The u of hydrated mineral fillers in poly-
olefin wire and cable formulations suffers
from a number of drawbacks, the majority of
which stem from the very high incorporation
level of mineral filler necessary to meet fire
retardant specifications such as UL-94 or
IEC 60332. To achieve any worthwhile level of
fire performance, filler loadings of up to
65 weight percent (wt.%) in polyolefins are
not uncommon. At this addition level, the filler
has a drastic effect on the system properties
and leads to compounds with a high specific
gravity and limited flexibility in addition to
low mechanical properties, especially elonga-
tion at break. Problems during compounding
may also be obrved due to the incread
viscosity of the formulation.
In view of such effects, the choice of polymer
is critical in achieving high performance HFFR
cable insulation and sheathing compounds.
In esnce, the polymer of choice must be
able to accept a high loading of flame retar-
dant filler with a minimal loss of mechanical
properties. As many cable producers and
compounders are discovering, ENGAGE™
Polyolefin Elastomer is a critical ingredient in
many successful HFFR formulations.
Before describing the performance of lect-
ed HFFR compounds bad on ENGAGE
resins, it is informative to illustrate the sig-
nificant influence of both the level of mineral
filler addition and the level of compatibilir
on the properties of an HFFR compound.
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EQUATION 1:
2Al(OH)3Al2O3+ 3H2O
at temperatures >180ºC with a
decomposition energy = 1050 J/g
EQUATION 2:生化危机5游戏
Mg(OH)2MgO + H2O
decomposition energy = 1250 J/g
Flame retardancy can be achieved in a number
of ways. For example, the addition of halogen
compounds (frequently ud in combination
with antimony trioxide) acts as radical traps
inhibiting the free radical chain reactions
involved in decomposing the polymer into
combustible gas; or the u of intumescent
formulations which form a protective layer of
foamed char which retards the burning of the
polymer insulation; or the addition of hydrated
mineral fillers which dilute the concentration
of flammable material and decompo below
the ignition temperature of the polymer
when expod to heat, releasing water and
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removing heat from the fire source.
In view of recent European legislation, there
are a growing number of wire and cable
applications requiring the u of halogen free
or non-PVC insulation or sheathing materials.
This has led to the growth of halogen free
flame retardant (HFFR) formulations bad on
the u of ethylene copolymers and hydrated
fillers such as aluminium hydroxide (ATH) or
magnesium hydroxide (MDH). In addition to
reducing the amount of organic material that
can decompo, hydrated mineral fillers func-
tion by the principle of an endothermic or
heat sink effect combined with the dilution of
the flammable decomposition gas by inert
water vapor. Considerable amounts of heat
are extracted from a fire scene as the hydrat-
ed filler decompos according to Equations
1 or
2 below.
two
™Trademark of The Dow Chemical Company Figures 1-6 show how the properties of a mineral-filled polyolefin composition vary as a function of mineral filler loading for a refer-ence HFFR formulation made with ENGAGE™Polyolefin Elastomer.
In general, the Limiting Oxygen Index (LOI)test gives an indication of the ea of com-bustion in an O 2-N 2atmosphere through the downward burning of a vertically mounted sample and is ud to give a uful compari-son of the relative flammability of different materials. Figure 1 shows approximately
60wt.% of ATH is needed in a standard poly-olefin formulation to achieve an LOI of >30. Figures 2-6 demonstrate the effect of this level of ATH addition on the compound vis-cosity and mechanical properties.
It is clearly shown in Figures 2-6 that at 60-65wt% ATH addition, compound hardness,viscosity, and flexural modulus are significantly incread relative to the pure polymer system.Obrve also how the compound elongation at break value is drastically reduced as the level of mineral filler increas.
As a result of the influence of mineral filler level, the compounder or formulator has to reach a compromi between achieving good flame retardant properties (as indicated by incread LOI figures) and the production of a compound which is readily processable and posss good mechanical properties.To illustrate the ability of ENGAGE Polyolefin Elastomer to accept high filler levels and thus achieve a > 30 LOI rating, a 65wt.%ATH has been chon as the standard level of hydrated filler in the reprentative HFFR formulations.
Weight%, ATH
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Figure 1:Effect of aluminium hydroxide (ATH) level
on compound Limiting Oxygen Index
Weight%, ATH
S h o r e D
Figure 2:Effect of aluminium hydroxide (ATH) level
on compound hardness (Shore D).
Weight%, ATH
160°C M o o n e y V i s c o s i t y
Figure 3:Effect of aluminium hydroxide (ATH) level
on compound viscosity (Mooney Viscosity at 160ºC)
Weight%, ATH
T e n s i l e S t r e n g t h (M P a )
Figure 4:Effect of aluminium hydroxide (ATH) level
on compound tensile strength.
Weight%, ATH
E l o n g a t i o n @ B r e a k (%)
Figure 5:Effect of aluminium hydroxide (ATH) level
on compound elongation at break.
Weight%, ATH
F l e x u r a l M o d u l u s (M P a )
Figure 6:Effect of aluminium hydroxide (ATH) level
on compound flexibility (flexural modulus).
three
The compatibility of the polar surface of the hydrated filler and a pure polyolefin such as ENGAGE™ Polyolefin Elastomer is limited,and as a conquence, the physical properties of a simple highly filled compound using ENGAGE resins are relatively poor. In order to enhance the mechanical properties of a polyolefin-hydrated mineral filled compound,some form of compatibilisation is needed between the polar filler surface and the inert polyolefin matrix.
Many filler suppliers have tackled this problem by supplying their fillers coated with carefully lected additives, for example vinyl silane coated ATH for polyethylene systems or amino silane coated fillers for ethylene vinyl acetate copolymers. Alternatively, the com-pounder can accomplish this coupling by adding the required silane mixture during the filler compounding process itlf where the silane reacts chemically with the surface of the hydrated filler.
An alternative procedure is to u small amounts of maleic anhydride grafted polymers (Mah-g-LLD
PE). Figures 7-10 illustrate how the properties of an HFFR compound made with ENGAGE resins with 65wt.% ATH vary as a function of Mah-g-LLDPE addition level.Considering the ea by which the maleic anhydride grafted polymer can be added to either an internal mixer or twin screw extruder,this system has been chon as the preferred compatibilising agent in HFFR systems. Bad upon the information prented, an addition level of around 5wt.% Mah-g-LLDPE in an HFFR formulation is recommended.
Weight%, Mah-g-LLDPE
L O I
Figure 7:Effect of Mah-g-LLDPE level
on compound LOI.
Weight%, Mah-g-LLDPE
160°C M o o n e y V i s c o s i t y
Figure 8:Effect of Mah-g-LLDPE level
on compound viscosity (Mooney Viscosity at 160ºC).
Weight%, Mah-g-LLDPE
T e n s i l e S t r e n g t h (M P a )
Figure 9:Effect of Mah-g-LLDPE level
on compound tensile strength.
Weight%, Mah-g-LLDPE
E l o n g a t i o n @ B r e a k (%)
Figure 10:Effect of Mah-g-LLDPE level
on compound elongation at break.
Take note, however, of the results from the modified hot pressure (knife)2test, a standard wire and c
able performance test. If carried out above the melting point of the ENGAGE Polyolefin Elastomer, penetration of the knife can reach 100%. Excellent resistance to knife penetration is achieved when the melting point of the ENGAGE resin exceeds that of the hot pressure test.
Processability of the final compound is also a very important characteristic of the HFFR formulation. Table 1 shows that the u of a low melt index ENGAGE product in an HFFR formulation (Compounds A-C) translates into a relatively high Mooney viscosity compound. However, consider Compounds D and E which u a higher flow resin such as ENR17256.00 or ENGAGE™ 8400. HFFR compounds bad on the grades have significantly lower Mooney viscosity figures. Thus the choice of ENGAGE resin grades clearly impacts the compound viscosity and, as a conquence, the processability of the final HFFR compound. If the objective of the HFFR formulation is a reduced viscosity compound, then the u of high flow grades of ENGAGE resins should be lected as part of the formulation.
The product range of ENGAGE™ Polyolefin Elastomers compris products having varying but nevertheless low levels of crystallinity. As a result, a number of grades are suitable as part of an HFFR formulation; however, the lower density grades are best able to accept large amounts of mineral filler while exhibiting a degree of flexibility and high elongation at break values in the final co
mpound.
This is illustrated by the formulations pre-nted in Table 1, which reveal that low density grades such as ENGAGE™ 8100 can yield flexible HFFR formulations which have a flexural modulus of around 100 MPa, a hard-ness down to 40 Shore D, and can maintain excellent elongation at break and tensile strength figures even at filler loading levels of 65wt.%.
As the crystallinity of the ENGAGE™ resin grade increas, the tensile strength of the compound increas; but this is also followed by a significant decrea in the elongation at break of the system. If the objective of an HFFR cable formulation is to increa system flexibility and/or elongation at break figures, then more amorphous low density grades should be lected as part of the formulation. Table 1:Properties of HFFR Formulations Bad on ENGAGE™ Polyolefin Elastomer
(at Varying Densities and Melt Indices)
Note: The internal data contained in Table 1 have been generated on compression molded plates from lab scale mixing experiments.
ENR designates an experimental, non-commercial product. If products
are described as “experimental” or “developmental”: (1) product specifi-
cations may not be fully determined; (2) analysis of hazards and caution
in handling and u are required; and (3) there is greater potential for
Dow to change specifications and/or discontinue production.
A laboratory pressure indentation screening test on a 20 mm x 2 mm
thick compression molded plate by a rectangular 0.7 mm thick knife with
a weight of 136g for 2 hours at the specified temperature.
four
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It is apparent that no single ENGAGE™ resin grade alone is likely to fulfill all target criterion for a thermoplastic HFFR compound when we are faced with many emingly contradictory formulation requirements, for example the desire for compound flexibility versus reduced indentation in the hot pres-sure test.
In an effort to meet the required property profile for a thermoplastic HFFR compound, the u of poly
mer blend systems using ENGAGE Polymer Elastomer is suggested. Such blends may take the form of a combina-tion of two ENGAGE resin grades or the blending of an elastomeric ENGAGE resin with a traditional higher density LLDPE or VLDPE material. Table 2 lists four such blends together with the reference ENR17256.00 system (Compound D).The Mah-g-LLDPE compatibilid ENR17256
reference (Compound D) has good flexibility,
a current deficiency of many highly filled
cable formulations, combined with excellent
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tensile properties and an elongation at break
value of over 230%. However, with a peak
melting point of 73ºC, the permanent defor-
mation in the 90ºC hot pressure test is 100%.
The additional formulations prented in
Table 2 illustrate how the performance of
HFFR compounds bad on ENGAGE™
Polyolefin Elastomer can be maximid for
u as cable insulation or sheathing.
For example, Compound F shows how defor-
mation resistance at 90ºC can be incread
by blending ENR17256.00 with LLDPE. The
addition of the higher crystallinity polymer
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also lifts the compound tensile strength;
however the addition of LLDPE negatively
impacts both compound hardness and flexi-
bility. Indeed, flexural modulus increas2022全国乙卷文综
almost three-fold over that of Compound D.
Studies have revealed that the hardness and
flexibility of the ENGAGE™ POE/LLDPE blend
can be reduced by lecting an elastomeric
compatibilir bad upon ENGAGE resin,
namely Mah-g-POE. The data on Compound G
prented in Table 2 show that not only is it
possible to formulate a compound which has
excellent hot pressure test performance, but
it can be done without sacrificing compound
hardness and flexibility. Indeed, this is the
goal of current advocates of HFFR systems,
namely to produce softer, more flexible
compounds which also posss deformation
resistance at elevated temperatures.
A glance at Table 2 also reveals that
Compound G has excellent tensile strength
and an elongation at break well above the元杂剧
125% minimum specification.
Table 2:Properties of ENGAGE™ POE/LLDPE HFFR Blends1
Internal data per Dow resources.
ENR designates an experimental, non-commercial product. If products are described as “experimental” or “developmental”: (1) product specifications may not be fully determined;
(2) analysis of hazards and caution in handling and u are required; and (3) there is greater potential for Dow to change specifications and/or discontinue production.
five™Trademark of The Dow Chemical Company
