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Hyperbranched polymers plasticizer Powered By Docstoc
					                         Novel Adhesion Promoters Based on

                               Hyper-branched Polymers

   H. Dodiuk-kenig(1), A. Buchman(3), and S. Kenig(1)(2)
   (1)
         Shenkar college of Enginnering and Design, Dep. of Plastics Eng., Ramat-Gan, Israel.
   (2)
         Israel Plastics and Rubber Center, Mitchel Building, Shenkar College, Israel
   (3)
         Rafael, Dep. 27, P.O.Box 2250, Haifa , Israel.

Abstract
    With the emergence of experimental and commercial highly branched polymers (HBPs)
   having two or three dimensional morphologies with high peripheral functionality, new
   opportunities have been created for formulating and tailoring new architectures for
   thermoset adhesives and related adhesion promoters.
    The authors studied a few adhesive systems previously, where the crosslinking agents
   had been either totally or partially replaced by the HBPs. In epoxy and polyurethane
   systems addition of poly-amido-amines (PAMAMs) HBPs, improved the mechanical and
   thermal properties of the adhesives due to increase of crosslinking density and formation
   of modified multi-phase morphologies having high-energy absorption network.
   In the present study the objective was to investigate the effects of HBP PAMAM primers
   on interfacial characteristics of epoxy and polyurethane bonded joints, using various
   substrates (Aluminum, Magnesium, plastics and fibers) prior and after exposure to a
   combination of heat and humidity. It was shown that the interfacial adhesion and the
   durability increase significantly (100-250%) in all the studied joints where PAMAMs
   were used for surface treatment.



Introduction

   With the emergence of low cost highly branched (HB) poly (amido-amines) (PAMAMs) (1)
   new avenues have been opened for enhancing the properties of epoxy systems, due to the
   modified branched network morphology.
     There are two major routes to synthesize highly branched polymer structures. The first
   through step-wise controlled synthesis. In this way regular structures are formed. However
this multi-step synthesis results in low yield, expensive products and large quantities of waste
products. Alternatively, highly branched macromolecules can be prepared by one or two
stages, resulting in a lower degree of branching, which retains the non-linear structure and
high number of functional reactive groups (2). This process is much simpler than the multi
stage one, leading to low cost processes and products.
The first publications related to hyperbranched polyamide resins emerged between1982 to
1985. The synthesis was based on the chemistry of amine-acrylic reactions (3). In this route
Tomalia (4-6) obtained by repetitive diamine alkylation with acrylate and amidiation of the
resulting ester groups, a dendri-polyamide with high molecular weight. This method, which is
a multi –stage process, is costly and involves a great deal of waste products. Other methods of
syntheses were further developed (7-14).
An innovative synthesis of highly branched poly-amido-amines was recently proposed (15-
16). The synthesis is based on epoxy-amine reactions (see Figure 1). The branching structure
is achieved by using a multi-functional core-making compound like tetra-functional diamine.
The process is based on two quantitative steps: diepoxy-amine addition and polyamide-epoxy
addition. In this way highly branched polymers were obtained having a molecular weight of
5000-15000 g/mole and hydrogen functionality of 30 to 45.




         Figure 1: Highly Branched Synthesis of Poly-Amido-Amine Polymers


   The process, which requires temperatures between 60 to 100° C, does not produce any
  waste products. To reduce viscosities especially for high molecular weight resins a
  plasticizer is used. It should be emphasized that the polyamidoamines (PAMAM) are
  soluble in regular organic solvents and are compatible with many oligomers and polymers
  such as: epoxy resins, amine hardeners, polyamide resins for hot melt adhesives, etc.
  The effects on properties of the novel highly branched (HB) PAMAM polymers were
  studied in epoxy as well as in polyurethane systems.
Structural epoxy adhesives based on DGEBPA system having high shear and peel
strengths in combination with a Tg of 80°C, were obtained using a novel cost effective
curing system that contained HB PAMAM (17). Shear strength as high as 25 MPa
combined with peel resistance of 4.7 N/mm were obtained. Formulations that did not
include the optimized amount of HB PAMAM, exhibited reduced shear, peel and Tg.
  In polyurethane systems (18) partial replacement (1 to 2%) of the polyol in the
isocyanate/polyol mixture with the HB PAMAM resulted in shear strength increase of 46
to 78%, compared to a formulation not containing HB, following room temperature curing.
Higher concentrations of the hyper-branched polymer resulted in reduced shear strength
due to plasticization. When post curing was used to enhance diffusion (80°C for 5 hrs.)
both shear and peel strength increased by 64% and 100%, respectively, compared to the
reference formulation.
The simultaneous increase of shear and peel strength is very unique to adhesive systems.
In most cases an increase in shear strength (higher cross-linking density) is accompanied
by a decrease in peel strength (lower toughness). The former unique phenomenon is
attributed to the incorporation of the 3D HB PAMAM that imparted 3D cross-linked
network architecture as well as an energy absorbing structure. Thus, it was concluded that
the 3D architecture that was obtained by the introduction of the 3D polymers, might lead to
new directions for enhancing simultaneously the shear and peel strength of epoxy as well
as polyurethane adhesives and coatings.
The current study is aimed at investigating the effect of HBP and Dendrimers based on
PAMAM chemistry, on the interfacial adhesion of epoxies and polyurethane adhesives
using various substrates and surface treatments for fibers in epoxy matrix.

Experimental
Four different HB PAMAMs were included in the study.
Polyester amide - PEA (Hybrane HA – 1300 product of DSM Research B.V., Netherlands)
(19). It is based on15 hydroxylic end groups (Fig. 2). The molecular weight Mn = 1300,
Tg< 0°C and it is soluble in ethanol. Three concentrations were used: 0.5, 1.0 and 1.5%
w/w in ethanol. The solution was applied by brushing, dried for 30 min. at room
temperature followed by 90°C for 30 min. Adherend used was Aluminum 2024 T3 bare or
chromic acid anodized (no sealing).
The adhesives included: Epoxy DGEBPA (Epon 815C) cured with linear amido amine
(Versamide 140 Product of Shell), Polyurethane 1 based on TDI (Toluidine Di Isocyanate)
cured with polyether polyol (EN – 4 / EN – 7 product of Conap USA). and Polyurethane 2
based on MDI (Methylene Di phenyl Isocyanate) cured with polyether polyol ( AH1 / VK
10 product of Bayer, Germany).




              Fig.2: Chemical composition of Polyester Amide (Hybrane HA 1300)


Two poly-amido-amine oligomers HB PAMAMs: The first (AD-102) having a
functionality of 45 and Mn of 12100 – high molecular weight (HMW). This material was
chosen because primary amines react with both epoxies and polyurethanes. Seven
concentrations were evaluated: 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 and 5.0 % w/w in ethanol.
The second (IB-100) having a functionality of 30 and. Mn of 6500 – low molecular weight
(LMW). Seven concentrations were used: 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 and 5.0 % w/w in
ethanol.
The solutions of the two HB PAMAMs were applied to the adherends by brushing. The
primed adherends were dried for 30 min. in air followed by 30 min. at 90°C.
Adherend used were: Aluminum 2024 T3 bare or chromic acid anodized (no sealing).
In some cases a silane treatment was used (3-glycidoxy- propyltriethoxysilane –A 187
product of Union Carbide. The solution comprised of ethanol/water/silane ratio of 80/20/2
hydrolized for 30 minutes and then for one hour at 90 C).
Polyetherimide (Ultem 1000 made by General Electric) and Magnesium (AZ 90 alloy
made by Ortal Ltd.).
Adhesives included: Epoxy DGEBPA (Epon 815C) cured with linear amido amine
(Versamide 140 Product of Shell). Polyurethane 1 (EN – 4 / EN – 7 product of Conap
USA).
Two PAMAM dendrimers: (G3 and G4 products of Aldrich), generation 3 and 4
respectively. They are both based on free amino groups with functionality of 32 and 64 and
Mn = 6909 and Mn = 14225, respectively. The dendrimers are provided in a solution of
20% and 10% respectively in methanol. This material was chosen because primary amines
react with both epoxies and polyurethanes, and because of its perfect dendritic structure.
Two concentrations were used: 0.05 and 0.1% w/w in methanol. The solutions were
applied on the adherends by brushing followed by drying for 2 hrs. at 105°C.
The adherends and adhesives used were identical to the ones used in the case of the HB
PAMAMs.
In all four PAMAMs Single Lap Shear (SLS) joints were prepared and tested according to
ASTM D-1002 at a loading speed of 2 mm/min. Some samples with the optimal
concentration of primer were exposed to 95% Relative Humidity (RH) and 50°C for 10
days prior to loading in order to study the durability of the various adhesion promoters
PAMAMs.
Scanning Electron Microscopy was used to investigate the interfacial morphology of
primed adherends and failure surfaces of the bonded joints.
The durability of adherends treated with optimal concentrations of the primer and bonded
with epoxy and polyurethane adhesives was tested on wedge joints (ASTM D-3762)
compared to non-primed ones. Crack length was measured after 1,8,24 hours and after 7
days exposure to 95% (RH) and 50°C.
The interfacial adhesion effect of the HB PAMAMs on fibers in epoxy composite systems
was investigated with laminates prepared by compression molding. The reinforcing fabrics
used were Aramid (Kevlar) and Poly-Benzo-Imidazole (PBI - Zylon). The fabrics were
first treated with 1.5% solution of HB PAMAM (AD 102) dried and then interleaved with
epoxy film structural adhesive and compression molded. In the Aramid based composite,
FM-73 (Cytec) was used as matrix. For the PBI based composites, AF-191 was used as
matrix. The laminates were cut into strips and tested for inter-laminar shear strength
(ASTM D-2344), and compared with the same laminates not including the surface
treatment with the HB PAMAM.
Results and Discussion
     SEM analysis of the primed Aluminum adherends with the HB polyester amide (PEA),
     indicated improper wetting of the surface using 1% solution (isolated drops), see Fig. 3.




                        ‫02------ ׀‬µ------- ‫׀‬
                  Fig. 3: SEM of aluminum surface after priming with Polyester amide(1%) (X2000)


    Table 1 summarizes the results of adhesion shear strength of Al adherends primed with the
    PEA and the effect of heat and humidity exposure.

    Table 1: Adhesion shear strength (Kg/cm2) of Al adherends
    primed with various concentrations PEA before and after heat / humidity exposure.

   PEA conc. (%)/           0            0.5            1.0             1.5                0.5
   Adhesive                                                                         50°C/ 95%RH/10d
   Polyurethane 1        58 ± 6           69 ± 9       31 ± 6        34.5 ± 9            58 ± 1
                          (C)*           (C)            (C)           (M/C )              (C )
    Polyurethane 2       97 ± 9          132 ± 15      29 ± 1         30 ± 8            85 ± 19
                          (C )           (C )           (C )           (C )               (C )
   Epoxy                  136 ± 10       177 ± 16       126 ± 19     118 ± 27          201 ± 24
                    (A/M)       (A/M)             (A)               (A)                (C/M)
*
C – Cohesive failure, M – Mixed failure, A – Interfacial failure

The PEA contains hydroxyl end groups, thus the crosslinking with epoxy and polyurethane is
very limited and the wetting is inhibited. From the Table it can be seen that at low
concentration of PEA the adhesion strength is increased by 20-33%, while at high
concentrations the adhesion strength decreased (even lower than the untreated ones). The
primer affects less the polyurethane adhesives than the epoxy adhesive. The optimal
concentration of the primer PEA hyperbranch is 0.5%. After exposure to heat / humidity the
adhesion strength of the polyurethane is reduced (probably due to degradation) while the
adhesion strength of the epoxy is increased (probably due to further crosslinking).

Table 2 and Fig. 3 present the adhesion shear strength of epoxy bonded Aluminum joints and
Table 3 and Fig. 4 depict the adhesion shear strength of polyurethane bonded Aluminun joints.
Both types of adhesively bonded joints were primed the high molecular weight HB PAMAM.


Table 2: Adhesion shear strength (Kg/cm2) of epoxy bonded Al adherends primed with various
concentrations of HMW HB PAMAM.
    PAMAM         No treatment         No              Chromic               Chromic
    Concentration                      treatment       Anodized (no          Anodized (no
      (w/w %)                          with A-187      seal)                 seal) + A-187
    0 (Ref.)          42 ± 6               70 ± 8          126 ± 9             148 ± 16
                       (A)*               (A/DIV)         (A/DIV)               (A/M)
      0.5            36 ± 10               40 ± 9         122 ± 10             128 ± 10
                    (A/DIV )                (A )          (A/DIV )             (A/DIV )
      1.0            49 ± 10               49 ± 6          152 ± 17             154 ± 11
                       (A )               (A/DIV)            (M )                (M )
      1.5             44 ± 7               58 ± 6          168 ± 9             169 ± 8
                       (A)                  (C)*            (M/C)                (M/C)
      2.0            46 ± 13               51 ± 7          220 ± 26            224 ± 24
                       (A )              (A/DIV )            (C )                (C )
      3.0               ---                  ---            173 ± 21            176 ± 10
                                                             (C )                (C )
    4.0              ---                  ---             159 ± 26              158 ± 9
                                                            (M/C)                (M/C)
    5.0              ---                  ---             149 ± 20             137 ± 10
                                                           (M/C )                (M )
*
 C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure
                 Normalized Shear Strength
                   1.6

                   1.4

                   1.2

                   1

                   0.8


                   0.6

                   0.4
                         0     0.5      1      1.5  2   3       4       5
                                               HB [%]

Fig. 3: The effect of HMW HB PAMAM concentration on Epoxy shear strength



                       Normalized Shear Strength
                          1.8
                             1.6
                             1.4
                             1.2
                              1
                             0.8
                             0.6
                             0.4
                                   0   0.5 1    1.5 2   3   4       5
Fig. 4: The effect of HMW HB PAMAM concentration on Polyurethane shear strength

Table 3: Adhesion shear strength (Kg/cm2) of polyurethane bonded Al adherends primed with
HMW HB PAMAM
                  PAMAM         No treatment         Chromic
                  Concentration                      Anodized (no
                    (w/w %)                          seal)
                  0 (Ref.)         51 ± 3                58 ± 6
                                 (A/DIV)*                  (C)
                    0.5            58 ± 9               70 ± 11
                                  (A/DIV )               (M/C )
                    1.0            62 ± 4               98 ± 10
                                  (A/DIV )                 (C )
                    1.5            44 ± 4               84 ± 12
                                     (A)                 (M/C)
                    2.0            35 ± 4                 93 ± 14
                                     (A )                (M/C )
                    3.0               ---                72 ± 5
                                                       (A/DIV )
                   4.0                ---                88 ± 6
                                                           (C)
                   5.0                ---               85 ± 10
                                                           (C )
*
 C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure



As evident from the figures and tables significant improvements in shear strength were
obtained by the priming of the aluminum adherends. For the epoxy adhesive the optimal
concentration of the primer is 2% while for Polyurethane it is 1%.
SEM results (Figure 5) show that the high Mw PAMAM forms a very thin uniform coating
over the adherend. High magnification reveals one-micron uniform structures. Micrographs of
the failure surfaces show good adhesion between the adhesive and the primed surface. Figures
6-9 show the failure surfaces of Al adherend bonded with the Epoxy adhesive. Fig.6 is a non-
primed Al adherend. The failure is interfacial in nature. Fig. 7 shows the failure surface of a
1% PAMAM primed Al adherend. In this case the failure is a mixed mode one. Fig. 8 shows
the failure surface of a 2% PAMAM primed Al adherend. In this case the failure is a mixed /
cohesive one. Fig. 9 shows the failure surface of a 3% PAMAM primed Al adherend. In the
latter case the failure is also mixed / cohesive in nature. Higher concentrations of PAMAMs
show interfacial failures, probably due to peeling of the thicker primer layers.
Polyurethanes exhibit lower shear strengths that are associated with mostly interfacial failure
mode types. Even at the optimal primer concentration (1%) the failure is still partly interfacial.
Fig. 10 shows the failure surface of a 1% PAMAM primed Al adherend. The failure is mixed /
adhesive, while the adhesion to the adherend is good.




Fig. 5: Typical structures of HMW PAMAM on Aluminum adherend (X 2000)
Fig. 6: Failure surface of non-treated Al – interfacial failure bonded with Epoxy adhesive X250




            Fig. 7: Failure surface of 1% PAMAM primed sample– mixed failure
                     Bonded with Epoxy adhesive X250




        Fig. 8: Failure surface of 2% PAMAM primed sample– mixed/cohesive failure
                 Bonded with Epoxy adhesive X250
  Fig. 9: Failure surface of 3% PAMAM primed sample– mixed/cohesive failure
           Bonded with Epoxy adhesive X250




Fig. 10: Failure surface of 2% PAMAM primed sample – mixed /adhesive failure
           Bonded with Polyurethane adhesive X3300.

To further study the durability of the bonded joints, Wedge type specimens were bonded for the
formulations exhibiting best results in shear – 1% for epoxy and 2% for polyurethane primed
joints. The Wedge specimens were characterized with respect to crack growth. Crack length was
measured as function of time at 95% RH, 50°C. Figures 11 and 12 present the Wedge test results
for epoxy and polyuethane, respectively. A rigorous examination indicates that the initial crack is
     interfacial and turns cohesive. In the case of the adhesively bonded epoxy joints the crack
     penetrates under the anodization layer. As can be learned from Figures 11 and 12, the effect of the
     HB PAMAM primer is highly significant, leading to a very durable interface. The durability in the
     case of the epoxy system is improved to a higher level compared to the polyurethane system.

                       105

                       100

                        95
                                          Epoxy without
                        90                treatment

                        85
                                          Epoxy-with 2%
                        80                AD-102 treatment
                        75
                             0   1 4 24 128
                                 Time [Hours]


Fig. 11: Crack propagation in epoxy bonded wedge specimen treated with 2% PAMAM



                       12
                        0
                       11
                        0                   PU-without
                       10                   treatment
                        0
                                             PU-with 1%
                        9
                        0
                                             AD-102 treatment
                        8
                        0
                        7
                        0
                        6
                        00       1    4  2 12
                                         4
                                 Time [Hours] 8


        Fig. 12: Crack propagation in polyurethane bonded wedge treated with 1% PAMAM
                    .
Table 4 summarizes the adhesion shear strengths of epoxy bonded Aluminun primed with the
low Mw HB PAMAM.

Table 4: Adhesion shear strength (Kg/cm2) of epoxy bonded Al adherends primed with low
Mw PAMAM

          PAMAM       No treatment         No                 Chromic
       Concentration                       treatment          Anodized (no
          (w/w %)                          with A-187         seal)
       0 (Ref.)           42 ± 6                70 ± 8            126 ± 9
                           (A)*               (A/DIV)            (A/DIV)
          0.5             67 ± 5                78 ± 6           117 ± 15
                         (A/DIV )            (A/DIV )           (A/DIV )
          1.0             69 ± 10              71 ± 9            154 ± 20
                         (A/DIV )             (A/DIV)               (M )
          1.5             74 ± 9               85 ± 10           190 ± 20
                          (A/M)                 (A/M)              (M/C)
          2.0             62 ± 5                68 ± 6           126 ± 20
                         (A/DIV )            (A/DIV )               (M )
          3.0             65 ± 6                 68 ± 13          173 ± 21
                         (A/DIV )            (A/DIV )             (M/C )
          4.0             58 ± 4                78 ± 3           149 ± 20
                         (A/DIV)              (A/DIV)            (A/DIV)
          5.0             60 ± 8               69 ± 16           106 ± 20
                         (A/DIV )             (A/DIV)            (A/DIV)
     *
      C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure

Comparison of the results for the high Mw PAMAM (Table 2) with the results for the low Mw
PAMAM (Table 4) leads to the conclusion that the optimal concentration of the HB PAMAM
that yields the highest shear strength, depends not only on the adhesive used, but also on the
MW and the functionality of the primer. For the Epoxy adhesive the optimal concentration of
the primer low Mw HB PAMAM is1.5% while for the high Mw HB PAMAM it is 2 %.
Table 5 and Table 6 present the adhesion shears strength of Al adherents primed with G3 and
G4 dendrimers bonded with Epoxy and Polyurethane adhesives, respectively.
Table 5: Adhesion shear strength (Kg/cm2) of epoxy bonded Al adherends primed with various
concentrations of G3 and G4.



       Dendrimer        Concentration       No                Chromic
                        (w/w %)             treatment         Anodized (no
                                                              seal)
        0 (Ref.)             0                 70 ± 8             126 ± 9
                                                      *
                                             (A/DIV)             (A/DIV)
          G-3              0.05                31 ± 5            168 ± 15
                                             (A/DIV )             (C / M )
          G-3                 0.1              30 ± 3             180 ± 38
                                              (A/DIV)               (C )
          G-4              0.05                25 ± 5             193 ± 25
                                              (A/DIV)              (M/C)
          G-4               0.1                30 ± 6             190 ± 22
                                             (A/DIV )              (M/C)
      *
       C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure

Table 6: Adhesion shear strength (Kg/cm2) of polyurethane bonded Al adherends primed with
various concentrations of G3 and G4


       Dendrimer        Concentration       No                Chromic
                        (w/w %)             treatment         Anodized (no
                                                              seal)
         0 (Ref.)             0                51 ± 3              58 ± 6
                                                      *
                                             (A/DIV)             (A/DIV)
           G-3              0.05               42 ± 8              40 ± 7
                                                 (A )                (A )
           G-3                 0.1             44 ± 4             58 ± 4
                                                 (A )               (C)**
           G-4              0.05               49 ± 4              55 ± 7
                                                 (A )               (C)**
           G-4               0.1              44 ± 10             44 ± 12
                                                 (A )               (C)**
      *
       C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure
      **
        C – The adhesive foamed during cure.

SEM micrographs taken for Epoxy joints showed that the dendrimer G3 exhibits a much more
delicate failure structure compared to G4. The failure mode of 0.1% G3 and G4 primed Al
adherend is mixed mode - partly interfacial and partly cohesive and show improved features
compared to that of 0.05%. Fig. 14 gives the failure mode of Epoxy joint primed with 0.1%
G3. The interface between the adhesive and adherend shows good adhesion to the subsrate and
the spherical clusters of the dendrimer primer.
The optimal concentrations of each of the primers studied were applied on PEI (Ultem 1000)
and Magnesium alloy (AZ-91). Table 7 summarizes the shear strength of the resulting bonded
joints. The results show that PAMAMs are effective for both Mg and PEI improving shear
strength. Best results for Mg were obtained in the case of the high Mw HB PAMAM which
improves shear strength by 169% and for PEI the low Mw HB PAMAM which improves shear
strength by 163%. The effect of HB and dendrimer PAMAMs on the adhesion characteristics
of aluminun, PEI and magnesium bonded joints based on epoxy and polyurethane adhesives, is
very significant.




          Fig. 13: Failure surface epoxy bonded Al adherends primed with
                  0.1% G3, X2500.

Table 7: Shear strength (Kg/cm2) of various adherends and PAMAMs

                 Adherend      PEI / PEI          Mg / Mg         Al / Al
    Primer (optimal Conc.)
    REF      0%               68.2 ± 15           74.4 ± 15          126 ± 9
                                       *
                              (A/DIV)             (A/DIV)           (A/DIV)
    HMW PAMAM                  87.5 ± 4           107.9 ± 7         220 ± 26
    2%                          (M )                (C )               (A )
    LMW PAMAM                111.7 ± 4             89.5 ± 7         190 ± 20
    1.5 %                        (C )              (C/M )              (A )
    PAMAM G4                   92.8 ± 7           77.5 ± 12         166 ± 12
    0.1 %                       (M )                (M )               (A )
      *
       C – Cohesive, M – Mixed, A – Interfacial, A/DIV – Interfacial divided failure
These phenomena can be attributed to the chemical interactions between the peripherial end
groups of the branched PAMAMs and the epoxy and polyurethanes at the joint interface.
Furthermore, the interactions of the branched PAMAMs with the metallic or organic
substrates may be of physical and chemical in nature, respectively. It seems that the hydroxyle
end groups of the PEA are less reactive with the adhesive systems that were included in the
study. Finally, the amount of the branched PAMAMs on the interface cannot be above a
certain threshold as plasticization and high primer thickness may result in inferior interfacial
strength.
The mechanical properties for Inter-Laminar Shear Strength (ILSS) characterized according to
ASTM D-2344, for the two kinds of laminates prepared using HB PAMAM are presented in Table
8.
The two laminates evaluated comprised of aramid (Kevla)r fabric primed with HMW
PAMAM 1.5%         and consolidated with 120 C cured structural adhesive (FM-73 product of
Cytec)and Zylon fabric primed with HMW PAMAM 1.5% and consolidated with 120 C cured
structural adhesive (AF-191 product of 3M).
Table 8: Inter-laminar shear strength (ASTM D- 2344) for laminates with and
without HMW PAMAM (AD 102)
                Laminate                     Inter-Laminar- Shear-
                                                Strength (MPa)

               Kevlar – non treated                   11.4 ± 0.5

                Kevlar – AD 102                       18.1 ± 1.9

                Zylon – non treated                    9.0 ± 0.8

                Zylon – AD 102                        12.6 ± 1.7



The results showed that composites made of primed HB HMW PAMAM Aramid and
PBI fibers in epoxy matrices, improved inter laminar shear strength
(Kevlar laminate shear strength increased by 160% and that of the Zylon by 140%).
These results indicate that chemical interactions take place between the HMW HB PAMAM
and the organic fibers.
Conclusions
  1. The use of hyper-branched polymers as primers for the Epoxy and
     Polyurethane adhesives resulted in improved shear strength and higher
     adhesion durability.
  2. The optimal concentration of the HB primes depends on the specific
     combination of adhesive and HB primer due to specific chemical
     interactions.
  3. For Epoxy the optimum concentration of the HMW HB PAMAM ( A
     D102) was 2% and for the LMW HB PAMAM (IB 100) was 1.5%.
  4. For PU the optimum amount of AD102 was 1% (the shear strength
     improved for both treated and untreated Al substrates).
  5. Dendrimers had a lower effect than HB. However a lower concentration
     was needed.
  6. Application of HB PAMAMs showed shear strength increase on various
     adherends –plastic and metal.
  7. Morphological observation by SEM of failure bonded joints indicated that
     good interfacial interactions were formed between the substrates and the
     HB primers.
  8. A significant improvement in inte-laminar shear strength was observed for
     the Aramid/Epoxy and PBI/Epoxy composites with fibers treated with the
     HMW HB PAMAM (AD102)
                                          20




References
1. O.A. Matthews, A.N. Shipway, J.J. Stoddart, “ Dendrimers-Branching
  out from Curiosities into New Technologies” Prog. Poly. Sci.,Vol. 23,
  No. 1, 1-56 (1998).
2. G.R. Newcome, C.N. Moorefild, F. Voegtle, “ Dendritic Molecules,
  Concepts, Syntheses and perspectives, 261, VCH Weinhiem, Germany
  (1996).
3. Eur. Pat. Appl. EP 66,366 (1982).
4. D.A. Tomalia, V. Berry, M. Hall, D.M. Hedstrand, “Starburst
  Dendrimers”, Macromolecules, Vol. 20, No. 5, 1164 (1987).
5. D.A. Tomalia, “ A New Class of Polymers: Starburst Dendritic
  Macromolecules”, Polymer, Vol. 17, No. 1, 117 (1985).
6. D.A. Tomalia and W.A.Goddard, “ Starburst Dendrimers”, Angew
  Chem., Vol. 102, No. 2, 119 (1990).
7. USA Patent – US 5,760,142 (1998).
8. Eur. Pat. Appl., EP 802,215 (1997).
9. US Patent, US 4,737,550 (1988).
10. US Patent, US 4,631,337 (1986).
11. US Patent, US 4,558,120 (1985).
12. Israel Patent Appl. 125,565 (1998).
13. US Pat. Appl. 09/295,320 (1999).
14. PCT/IL Patent 99/00540 , “Highly Branched Oligomers, Process for
  Their Preparation and Applications Therof.
15 .L.Moshinsky, S.Kenig, H.Dodiuk-Kenig and A.Buchman, “Epoxy
  Adhesives and Primers Based on Hyperbranched Polyamidoamines”,
  Meeting of the Adhesion Society, Williamsburg, Virginia, Feb.2000.
16. L.Moshinsky, Epoxy Resins and Hardeners – Structure, Properties,
  Chemistry and Topology of Curing”, 370, Academia Press Ltd. Tel
  Aviv Israel, Russ (1995).
17. Unpublished results
18. H.Dodiuk, Z. Gold and S. Kenig , submitted to publications
19. HYPERBANE™ DSM New business development, 99-36 (1999).




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