Page 168 - Handbook of Adhesion Promoters

8.17 Polypropylene 161

8.17 POLYPROPYLENE

Many commercial adhesion promoters can be used in polypropylene, including Dynasy-
lan, Fusabond, Eastman Advantis, AP, CP, and G, Regalite, Resalloy, and Tyzor. There are
too many products to be listed by their grade names here but a full account of these addi-
tives can be found in Databook of Adhesion Promoters which also contains additional
information on the use of these additives.
Excellent adhesion to low surface energy materials, such as polypropylene, was
1
obtained by acrylate polymerization initiated by trialkylborane at room temperature. The
1
graft resulted from the hydrogen abstraction by alkoxyl and other radicals. These radicals
came from the oxidation of trialkylborane through the cleavage of O−O bond of
1
R BOOR. Polar or unsaturated groups were generated on the surface of low surface
2
1
energy material (PP) treated with trialkylborane.
Maleated polypropylene was used to promote adhesion between wood particles and
2
polypropylene matrix. The effect of adhesion promoter is less pronounced for particles
with large aspect ratio, mostly because of fiber fracture both parallel and perpendicular to
2
the fiber axis.
Mechanical interlocking by imprinting of undercut micropatterns was used for the
improvement of adhesive strength of polypropylene (see Figure 2.6 and explanation in the
3
text). The adhesive strength with the general-purpose epoxy adhesive at the 25° undercut
3
angle was 1.7 times higher than that of the specimen without surface modification.
Glass fiber coated with polyaniline was used for reinforcement of polypropylene. 4
Polypropylene grafted with maleic anhydride was used as an adhesion promoter for these
4
composites. Figure 2.22 shows that the polyaniline coating of glass fiber causes tran-
scrystallization which may be the cause of excellent adhesion. 4
Polypropylene and polypropylene/ethylene-propylene copolymer blend injection-
molded plates were painted with a chlorinated polypropylene-based adhesion promoter. 5
XPS data show that the Cl atomic fraction is less than 0.5% on the polymer blend side and
close to 4% on the paint side indicating that the fracture is located at the chlorinated poly-
5
propylene-polymer interface. The adhesion improvement induced by the presence of eth-
ylene-propylene copolymer nodules can be explained by energy dissipation occurring
5
during ethylene-propylene copolymer deformation.
Polypropylene was plasma treated and
tetraethoxysilane coated to improve adhe-
6
sion. High strength and cohesive failure
were obtained when combining treatments
for bonding with polyurethane adhesive. 6
Plasma treatment leads to the creation of
active oxidized functional groups on the
polypropylene surface which can then react
6
with silane and polyurethane adhesive.
Figure 8.7. Cross-section of fractured 30 wt% aspen
fiber-polypropylene composites (a) without maleated Fusion proteins composed of
anhydride polypropylene and (b) with 2 wt% maleated enhanced green fluorescent protein (EGFP)
anhydride polypropylene. [Adapted, by permission, and anchor peptides (e.g., cecropin A or
from Xue, Y; Veazie, DR; Glinsey, C; Horstemeyer, MF;
Rowell, RM, Composites Part B: Eng., 38, 2, 152-8, LCI) were applied to polypropylene sur-
2007.] faces to be used as an adhesion promoter. 7