U.S. patent application number 14/938431 was filed with the patent office on 2016-03-24 for structural polymer insert and method of making the same.
The applicant listed for this patent is FORD GLOBAL TECHNOLOGIES, LLC, MAZDA MOTOR CORPORATION. Invention is credited to Larry P. HAACK, Ann Marie STRACCIA, Kazuhisa To, Matthew John ZALUZEC.
Application Number | 20160082474 14/938431 |
Document ID | / |
Family ID | 41011293 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160082474 |
Kind Code |
A1 |
ZALUZEC; Matthew John ; et
al. |
March 24, 2016 |
STRUCTURAL POLYMER INSERT AND METHOD OF MAKING THE SAME
Abstract
A structural polymer insert. The insert includes a substrate
having a surface and an adhesive with the substrate being an
admixture of a polypropylene component and a glass fiber component.
The surface has a plurality of oxygen atoms, optionally introduced
by air plasma, in an amount of 1 to 60 atomic percent of all the
atoms present on the surface. The foam adhesive is attached to the
surface through one or more reactive moieties resulted from
oxidative action of the oxygen atoms.
Inventors: |
ZALUZEC; Matthew John;
(Canton, MI) ; HAACK; Larry P.; (Ann Arbor,
MI) ; STRACCIA; Ann Marie; (Southgate, MI) ;
To; Kazuhisa; (Novi, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FORD GLOBAL TECHNOLOGIES, LLC
MAZDA MOTOR CORPORATION |
Dearborn
Hiroshima |
MI |
US
JP |
|
|
Family ID: |
41011293 |
Appl. No.: |
14/938431 |
Filed: |
November 11, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12059230 |
Mar 31, 2008 |
9217066 |
|
|
14938431 |
|
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Current U.S.
Class: |
427/534 |
Current CPC
Class: |
B05D 7/02 20130101; C08J
7/0427 20200101; Y10T 428/269 20150115; C08J 7/123 20130101; C08J
2463/00 20130101; Y10T 428/28 20150115; Y10T 428/249984 20150401;
B05D 3/144 20130101; C08J 2323/12 20130101 |
International
Class: |
B05D 3/14 20060101
B05D003/14; B05D 7/02 20060101 B05D007/02 |
Claims
1. (canceled)
2. A method, comprising: air-plasma treating a surface of a polymer
substrate including 10-50 weight percent glass fibers, the
air-plasma treatment exposing a plurality of glass fibers from
beneath the surface and forming reactive moieties on the surface;
and applying an adhesive to the surface to form a plurality of
chemical bonds between the adhesive and the reactive moieties and a
plurality of mechanical bonds between the adhesive and the
plurality of exposed glass fibers.
3. The method of claim 2, wherein the adhesive is an expandable
foam adhesive.
4. The method of claim 2, wherein the air-plasma treatment deposits
oxygen atoms on the surface such that the surface includes 10 to 50
atomic percent oxygen after the air-plasma treatment.
5. The method of claim 2, wherein the air-plasma treatment deposits
nitrogen atoms on the surface such that the surface includes 0.1 to
10 atomic percent nitrogen after the air-plasma treatment.
6. The method of claim 2, wherein the air-plasma treatment deposits
silicon atoms on the surface such that the surface includes up to 5
atomic percent silicon after the air-plasma treatment.
7. The method of claim 2, wherein the air-plasma treatment deposits
oxygen and nitrogen atoms on the surface such that the surface
includes an oxygen-to-nitrogen atomic ratio of 5.0 to 12.0.
8. The method of claim 2, wherein the polymer substrate includes
glass fibers having a mean fiber length of at least 2 mm.
9. The method of claim 2, wherein the air-plasma treatment exposes
the plurality of glass fibers from up to 80 .mu.m beneath the
surface.
10. The method of claim 2, wherein the polymer substrate includes
about 30 weight percent glass fibers and the glass fibers have a
mean fiber length of about 3 mm.
11. The method of claim 2, wherein the polymer substrate is
polypropylene.
12. The method of claim 2, wherein the reactive moieties include
one or more of hydroxyl, ether, ketone and carboxyl moieties.
13. A method, comprising: air-plasma treating a surface of a
polymer substrate including glass fibers having a mean fiber length
of at least 2 mm, the air-plasma treatment exposing a plurality of
glass fibers from beneath the surface and forming reactive moieties
on the surface; and applying an adhesive to the surface to form
chemical bonds between the adhesive and the reactive moieties and
mechanical bonds between the adhesive and the plurality of exposed
glass fibers.
14. The method of claim 13, wherein the air-plasma treatment
deposits oxygen, nitrogen, and silicon atoms on the surface such
that the surface includes 10 to 50 atomic percent oxygen, 0.1 to 10
atomic percent nitrogen, and up to 5 atomic percent silicon after
the air-plasma treatment.
15. The method of claim 13, wherein the polymer substrate includes
10-50 weight percent glass fibers.
16. The method of claim 13, wherein the air-plasma treatment
deposits oxygen and nitrogen atoms on the surface such that the
surface includes an oxygen-to-nitrogen atomic ratio of 5.0 to
12.0.
17. The method of claim 13, wherein the polymer substrate is
polypropylene.
18. The method of claim 13, wherein the adhesive is an expandable
foam adhesive.
19. A method, comprising: air-plasma treating a surface of a
polypropylene substrate including glass fibers, the air-plasma
treatment exposing a plurality of glass fibers from beneath the
surface and forming reactive moieties on the surface; and applying
a foam adhesive to the surface to form a plurality of chemical
bonds between the foam adhesive and the reactive moieties and a
plurality of mechanical bonds between the foam adhesive and the
plurality of exposed glass fibers.
20. The method of claim 19, wherein the foam adhesive has a volume
expansion of 150 to 450 percent.
21. The method of claim 19, wherein the polypropylene substrate
includes 10-50 weight percent glass fibers, the glass fibers have a
mean fiber length of at least 2 mm, and the air-plasma treatment
deposits oxygen, nitrogen, and silicon atoms on the surface such
that the surface includes 10 to 50 atomic percent oxygen, 0.1 to 10
atomic percent nitrogen, and up to 5 atomic percent silicon after
the air-plasma treatment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. application Ser. No.
12/059,230 filed Mar. 31, 2008, the disclosure of which is hereby
incorporated in its entirety by reference herein.
TECHNICAL FIELD
[0002] At least one aspect of the present invention relates to a
structural polymer insert having glass fiber filled polypropylene
bonded to an adhesive.
BACKGROUND
[0003] Metal support structures are often used in the automotive
industry to provide strength and energy absorbency into vehicle
frames. In situations where certain specifications are mandated by
governmental requirements for safety and crash worthiness, glass
fiber reinforced polyamide inserts are commonly used in addition to
the metal support structures.
[0004] However, the glass fiber reinforced polyamide inserts have
met with limited use for various reasons, particularly because
polyamide often lacks requisite engineering durability.
Additionally, polyamide is a relatively expensive material which
has discounted substantially the widespread use of the structural
polyamide inserts.
SUMMARY
[0005] According to at least one aspect of the present invention, a
structural polymer insert is provided. In at least one embodiment,
the structural polymer insert has a substrate and an adhesive with
the substrate being an admixture of a polypropylene component and a
glass fiber component. The substrate has a surface and the surface
has a plurality of oxygen atoms in an amount of 1 to 60 atomic
percent of the total atoms present on the surface. The adhesive is
attached to the surface through one or more reactive moieties
formed by the oxidative action of the oxygen atoms. In at least one
embodiment, the one or more reactive moieties illustratively
include hydroxyl, ether, ketone, carboxyl, or any combination
thereof.
[0006] In at least one embodiment, the substrate surface has a
number of nitrogen atoms in an amount of 0.1 to 10 atomic percent
of the total atoms present on the surface.
[0007] In at least one embodiment, the surface has a number of
silicon atoms in an amount of 0 to 5 atomic percent of the total
atoms present on the surface.
[0008] In at least one embodiment, the substrate surface has an
oxygen-to-nitrogen atomic ratio of 5.0 to 12.
[0009] In at least one embodiment, the glass fiber component is in
the range of 1 to 60 weight percent and in at least one particular
embodiment of 30 to 50 weight percent of the total weight of the
substrate. In at least another embodiment, the glass fiber
component has a mean fiber length no less than 2 millimeters.
[0010] In yet at least one embodiment, the adhesive is an
expandable foam adhesive and in at least one particular embodiment
the foam adhesive is epoxy based.
[0011] According to at least one aspect of the present invention, a
process is also provided. In at least one embodiment, the process
includes providing a substrate having a surface, the substrate
being an admixture of a polypropylene component and a glass fiber
component; introducing a plurality of oxygen atoms on the surface
to form a treated surface; and attaching an adhesive to the surface
to produce a bonded article. The process optionally further
includes curing the bonded article under heat. In at least one
particular embodiment, the introducing is mediated by air plasma
treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows XPS (X-Ray Photoelectron Spectroscopy) survey
spectra of GFPP (glass fiber filled polyproylene) specimens having
30 percent by weight of glass fiber component with a mean fiber
glass length of 3 millimeters, before and after air plasma
treatment;
[0013] FIGS. 2A and 2B depict XPS C (Carbon)1s core level spectrum
of the GFPP specimens in FIG. 1, before (2A) and after (2B) of the
air plasma treatment;
[0014] FIG. 3 shows XPS C is core level spectra of GFPP specimens
having 30 percent by weight of glass fiber component with a mean
glass fiber length of 3 millimeters, without and with air plasma
treatment at dosage "a" and dosage "b";
[0015] FIG. 4 illustrates 20.times.-magnification surface roughness
using topography measurements;
[0016] FIG. 5 illustrates optical stereomicrographic surface images
of various GFPP specimens, without and with air plasma treatment at
dosage "a" and dosage "b", respectively;
[0017] FIG. 6 shows topography measurements presenting
100.times.-magnification surface roughness of the GFPP specimens,
without or with air plasma treatment at dosage "a" and dosage "b",
respectively;
[0018] FIGS. 7A-7F demonstrate a 3-dimensional topography, at
20.times. or 100.times.-magnification, of various GFPP specimens,
without or with air plasma treatment at dosage "a" and dosage "b",
respectively, with FIGS. 7A, 7B, and 7C depicting topographic
results of no air plasma, dosage "a", and dosage "b", respectively,
at 20.times. magnification and FIGS. 7D, 7E, and 7F depicting
topographic results of no air plasma, dosage "a", and dosage "b",
respectively, at 100.times. magnification;
[0019] FIG. 8 depicts boxplots showing the mean and distribution of
lapshear bond strength measurements (five replicates per group) of
pure polypropylene specimens, without or with air plasma treatment
at dosage "a" and dosage "b", respectively;
[0020] FIG. 9 depicts boxplots showing the mean and distribution of
bond failure mode (five replicates per group) of pure polypropylene
specimens, without or with air plasma treatment at dosage "a" and
dosage "b", respectively;
[0021] FIG. 10 depicts boxplots showing the mean and distribution
of lapshear bond strength measurements (five replicates per group)
of various GFPP specimens, without or with air plasma treatment at
dosage "a" and dosage "b", respectively;
[0022] FIG. 11 depicts boxplots showing the mean and distribution
of bond failure mode (five replicates per group) of various GFPP
specimens, without or with air plasma treatment at dosage "a" and
dosage "b", respectively;
[0023] FIG. 12 depicts boxplots showing the mean and distribution
of bond failure mode (five replicates per group) of various GFPP
specimens, without or with air plasma treatment at dosage "a" and
dosage "b", as a function of plasma dosage, glass fiber content,
and glass fiber length;
[0024] FIG. 13 depicts boxplots showing the mean and distribution
of lapshear bond strength measurements (five replicates per group)
of various GFPP specimens, without or with air plasma treatment at
dosage "a" and dosage "b", as a function of plasma dosage, glass
fiber content, and glass fiber length;
[0025] FIG. 14 depicts main effects plots for the response of bond
strength, without or with air plasma treatment at dosage "a" or
"b", as a function of the factors air plasma dosage, glass fiber
content, and glass fiber length;
[0026] FIG. 15 depicts main effects plots for the response %
cohesive failure, without or with air plasma treatment at dosage
"a" or "b", as a function of the factors: air plasma dosage, glass
fiber content, and glass fiber length; and
[0027] FIG. 16 depicts boxplots of lapshear bond strength of
various GFPP lapshear specimens having either "short" mean fiber
length or "long" mean fiber length.
DETAILED DESCRIPTION
[0028] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale; some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for teaching one skilled in the art to variously employ the present
invention.
[0029] Reference will now be made in detail to compositions,
embodiments, and methods of the present invention known to the
inventors. However, it should be understood that disclosed
embodiments are merely exemplary of the present invention which may
be embodied in various and alternative forms. Therefore, specific
details disclosed herein are not to be interpreted as limiting,
rather merely as representative bases for teaching one skilled in
the art to variously employ the present invention.
[0030] Except where expressly indicated, all numerical quantities
in this description indicating amounts of material or conditions of
reaction and/or use are to be understood as modified by the word
"about" in describing the broadest scope of the present invention.
Practice within the numerical limits stated is generally
preferred.
[0031] The description of a group or class of materials as suitable
for a given purpose in connection with one or more embodiments of
the present invention implies that mixtures of any two or more of
the members of the group or class are suitable. Description of
constituents in chemical terms refers to the constituents at the
time of addition to any combination specified in the description,
and does not necessarily preclude chemical interactions among
constituents of the mixture once mixed. The first definition of an
acronym or other abbreviation applies to all subsequent uses herein
of the same abbreviation and applies mutatis mutandis to normal
grammatical variations of the initially defined abbreviation.
Unless expressly stated to the contrary, measurement of a property
is determined by the same technique as previously or later
referenced for the same property.
[0032] As used herein and unless otherwise indicated, the term
"GFPP" is interchangeably used with the term "glass fiber filled
polypropylene".
[0033] According to at least one embodiment of the present
invention, a structural polymer insert with industrially acceptable
engineering durability and comparably enhanced economical
efficiency is disclosed. In at least one embodiment, the structural
polymer insert includes a glass fiber filled polypropylene (GFPP)
bonded to a foam adhesive with relatively enhanced lapshear bond
strength therebetween.
[0034] It has been surprisingly found that a synergistic effect on
the bond strength between a glass fiber filled polypropylene
substrate and a foam adhesive is realized by an interplay of at
least three variables, namely strength and extent of a surface
treatment, total weight percentage of the glass fiber component,
and length of the glass fibers. In at least one embodiment and as
will be described in more detail below, an exemplary air plasma
treatment may deliver two separate modes of impact. A first mode is
realized when the air plasma is delivered to oxidize the substrate
surface carbon moieties to effectuate chemical bond formation
between the foam adhesive and the substrate through the oxidized
carbon moieties. In at least another particular embodiment, a
second mode of impact is delivered when the air plasma further
induces surface roughness by etching certain portions of the glass
fiber component. These exposed glass fibers may subsequently form
mechanical bonds with the foam adhesive so that the bond strength
between the foam adhesive and the substrate is further
strengthened.
[0035] In at least one embodiment, and as will be described in more
detail below, inclusion of the glass fiber component functions both
to provide structural durability and to maximize the air plasma
impact on the bond strength. The inclusion of glass fibers in the
polypropylene polymers substantiates the bond strength enhancing
effect elicited by the air plasma treatment by at least five (5)
folds, as compared to a polypropylene counterpart with zero glass
fiber content.
[0036] Since the air plasma treatment may be altered in dosage and
at certain dosage may etch the substrate up to 80 microns deep from
a surface of the substrate, it seems at first glance that the
higher the air plasma dosage, the more mechanical bonds, the
greater the bond strength. However, a trade-off is found to exist
between increases in bond strength verses air plasma intensity.
While certain high dosage air plasma creates a rougher surface, yet
at the same time, the high dosage air plasma may also induce some
over-oxidation of the carbon species on the substrate surface and
hence a reduction on the extent of effective surface oxidation.
[0037] As will be described in more detail below, surface carbon
over-oxidation may reduce, to some extent, the amount of oxidized
carbon species on the substrate surface and therefore weakens bond
strength intensity. As such, providing a structural polymer insert
with relatively enhanced bond strength is at least effectuated by
the synergistic interplay of the above-mentioned factors.
[0038] Conventional structural inserts are manufactured using
polyamide or nylon. Nylon is a thermoplastic silky material made of
repeating units linked by peptide bonds or amide bonds. Nylons are
condensation copolymers formed by reacting equal parts of a diamine
and a dicarboxylic acid, so that peptide bonds form at both ends of
each monomer in a process analogous to polypeptide biopolymers.
Solid nylon is used for mechanical parts such as gears and other
low- to medium-stress components previously cast in metal.
Engineering grade nylon is processed by extrusion, casting, and
injection molding.
[0039] Unlike nylon, polypropylene is a versatile and more
cost-effective engineering thermoplastic material. For example, an
exemplary going price for glass fiber filled polypropylene is at
least forty percent lower than the price for a polyamide
counterpart. The cost effectiveness in utilizing the glass fiber
filled polypropylene as a component for a structural insert is
furthered since the glass fiber filled polypropylene may be
manufactured at faster cycle times than the polyamide counterpart.
In addition, polypropylene is a thermoplastic polymer having
industrially acceptable resistance to fatigue. Polypropylene has a
melting point of 160 degrees Celsius. Many plastic items for
medical or laboratory use are made from polypropylene because
polypropylene can withstand the heat in an autoclave. However,
polypropylene suffers from having chemically inert and nonporous
surfaces with low surface tensions, as such, raw polypropylene
polymers are generally non-receptive to bonding with printing inks,
coatings and adhesives. In one or more embodiments, it is an object
to increase bonding strength of the polypropylene polymers to foam
adhesives so as to provide cost-effective structural plastic
inserts with bonding strength suitable for industrial
engineering.
[0040] In at least one embodiment, a structural polymer insert
includes a substrate and an adhesive bonded to the substrate. The
substrate is composed of a polypropylene component and a glass
fiber component, both components are intermixed with each other.
The substrate has a surface which has a plurality of oxygen atoms
in an amount of 1 to 60 atomic percent of the total atoms present
on the surface. In at least one particular embodiment, the amount
of the oxygen atoms is of 10 to 50 atomic percent of the total
atoms present on the surface.
[0041] In at least one embodiment, the polypropylene component is a
number of polypropylene polymer molecules having a weight
percentage in the range of 40% to 95% of the total weight of the
substrate.
[0042] In yet at least one embodiment, the glass fiber component
has a weight percentage of 1% to 60%, in at least another
embodiment of 10% to 50%, and in at least another particular
embodiment of 30% to 50% of the total weight of the substrate.
[0043] In yet at least one embodiment, the glass fiber component is
a collection of glass fibers having a mean fiber length no less
than 2 millimeters. To ensure a certain mean fiber length, the
substrate may be molded by combining the polypropylene component
and the glass fiber component using low shear screws under
conditions that retain the glass fiber length. Conversely,
substrates with short glass fibers are molded with high shear screw
under conditions enabling the shortening of the glass fibers.
[0044] The polypropylene component and the glass fiber component
can be combined and admixed using any suitable methods known in the
art. One exemplary method is shown in U.S. Pat. No. 3,654,219 to
Boyer et al., the content of which is incorporated herein in its
entirety by reference. The resulting mixture is optionally
subjected to heat curing at a temperature of at least 120 degrees
Celsius and preferably at least 135 degrees Celsius. Depending on
the particular application involved, the substrate may be molded
into various configurations including the configuration where the
surface takes the form of a pocket or a cavity.
[0045] The adhesive may be expandable or non-expandable depending
on the particular application involved. In at least one embodiment,
the adhesive is a foam adhesive that is expandable under certain
condition which may be externally applied. The condition
illustratively includes temperature, pressure, and/or chemistry. By
way of example, the foam adhesive may be sensitive to heat and
expandable upon the application of a high temperature in the range
of 120 to 180 degrees Celsius. The foam adhesive illustratively
includes adhesive that is epoxy-based, urethane-based, or
silane-based. The epoxy-based foam adhesives are heat expandable
and when cured, are more heat- and chemical-resistant than those
cured at room temperature. The epoxy-based foam adhesives suitable
for forming the structural polymer insert have a typical volume
expansion of 150 to 450 percent, in one particular instance of 200
to 400 percent, and in another particular instance of 250 to 350
percent. In at least one embodiment, the GFPP substrate is bonded
to the foam adhesive and the resulting bonded article is subject to
curing. The curing may be carried out under any suitable condition
and in at least one particular embodiment under an externally
applied heat upon which the foam adhesive undergoes a heat-assisted
volume expansion. In at least one particular embodiment, the bonded
article is pre-heated at a temperature from 100 to 200 degrees
Fahrenheit. In at least another particular embodiment, the
pre-heated bonded article is subject to further heat of a
temperature from 200 to 300 degrees Fahrenheit.
[0046] In at least one embodiment, the adhesive is attached to the
surface of the substrate through at least one connective bond. The
connective bond illustratively includes a chemical bond, a
mechanical bond, or any combination thereof. The chemical bond may
be a hydrogen bond, a van der Waals' bond, an ionic bond, or a
covalent bond. By way of example, the covalent bond is formed
between one or more reactive moieties present on the surface of the
substrate with the reactive moieties illustratively including
ether, hydroxyl, ketone, and carboxyl. These reactive moieties are
various chemical states of carbon atoms that are oxidized by oxygen
atoms.
[0047] In at least one embodiment, the oxygen atoms are delivered
onto the surface through application of a surface treatment.
Surface treatment improves bonding characteristics between the
substrate and the foam adhesive, e.g., by increasing the
substrate's inherent surface energy. The surface treatment is
applied to the substrate surface to modify surface roughness and/or
to facilitate the conversion of surface atoms such as carbon atoms
to carbon species having reactive moieties. Suitable surface
treatment illustratively includes air plasma, Corona, UV/ozone
flame plasma, chemical plasma, or other atmospheric plasma using
nitrogen or helium as carrier gas.
[0048] Corona plasma generally uses a high-frequency power
generator, a high-voltage transformer, a stationary electrode, and
a treater ground roll. Standard utility electrical power is
converted into higher frequency power which is then supplied to a
treater station. The treater station applies this power through
ceramic or metal electrodes over an air gap onto a surface to be
treated.
[0049] Flame plasma treaters generate typically more heat than
other treating processes, but materials treated through this method
tend to have a longer shelf-life. These plasma systems are
different than air plasma systems because flame plasma occurs when
flammable gas and surrounding air are combusted together into an
intense blue flame. Surfaces are polarized from the flame plasma
affecting the distribution of the surfaces' electrons in an
oxidation form. Due to the high temperature flammable gas that
impinges on the surfaces, suitable methods should be implemented to
prevent heat damages to the surfaces.
[0050] As known in the art, chemical plasma is often categorized as
a combination of air plasma and flame plasma. Somewhat like air
plasma, chemical plasma is delivered by an electrically charged
air. Yet, chemical plasma also relies on a mixture of other gases
depositing various chemical groups onto a to-be-treated surface.
When a chemical plasma is generated under vacuum, surface treatment
may be effectuated in a batch process (such as when an article is
singly located within a vacuumed chamber for treatment) rather than
an in-line process (such as when a plurality of articles are
sequentially lined-up for treatment).
[0051] Air plasma is similar to Corona plasma yet with differences.
Both air plasma and Corona plasma use one or more high voltage
electrodes which positively charge surrounding air ion particles.
However in air plasma systems, the rate oxygen deposition onto a
surface is substantially higher. From this increase of oxygen, a
higher ion bombardment occurs. By way of example, an exemplary air
plasma treatment method is illustratively detailed in the U.S.
Patent Publication titled "Method of Treating Substrates for
Bonding" (publication number US 2008-0003436), now U.S. Pat. No.
7,744,984 the content of which is incorporated herein in its
entirety by reference.
[0052] In at least one embodiment, various atoms are being
deposited onto or become exposed upon the substrate surface through
the air plasma equipment. Atoms being elicited on the substrate
surface illustratively include oxygen atoms, nitrogen atoms, and
silicon atoms. The oxygen atoms, in particular, consequently induce
the oxidation of carbon atoms on the substrate surface and the
transformation thereof to reactive moieties in the form of ether or
hydroxyl, carbonyl, and carboxyl, with the hydroxyl moiety being
the most reactive in causing covalent bond formation between the
substrate and the foam adhesive.
[0053] In at least one embodiment, topography is used to measure
surface roughness of the PP (pure polypropylene with zero glass
fiber content) and the GFPP specimens upon an air plasma treatment.
Topography measurements are usually made using optical profilometry
with a Wyko NT-3300 system. Surface characterization of a surface
may be performed by using X-ray photoelectron spectroscopy (XPS).
X-ray photoelectron spectroscopy surface characterization
measurements relate increased bond strength to the presence of
surface hydroxyl functionality that enables the formation of
covalent bond linkage to a foam adhesive. The instrument
illustratively used may be Kratos AXIS 165 Electron Spectrometer
manufactured by Kratos Analytical, Manchester, England.
Photoelectrons are generated using a monochromatic Al K-alpha
(1486.6 eV) x-ray excitation source operated at 15 kV, 20 mA (300W)
and collected using hybrid mode magnification with the analyzer at
a 20 eV pass energy for high resolution spectra, and a 80 eV pass
energy for elemental surveys. High-resolution C is core level
spectra is acquired for specification of carbon oxidation
chemistry. The C 1 s core level refers to electrons that reside in
the carbon 1 s orbital atomic core level. The XPS C 1s core level
spectrum is the spectrum of photo-electron emission that occurs
from the C (carbon) is core level as a consequence of sample
irradiation by Al K-alpha X-rays. Quantification of survey data is
accomplished by procedures based on Scofield photoionization
cross-section values. A least-squares based fitting routine is used
to peak fit the high-resolution core level spectra. The
least-squares based fitting routine is used whereby peaks are added
manually based on best judgment and the routine is allowed to
iterate freely on peak height, peak width, and binding energy
position to synthesize a C (carbon) 1s envelope that most closely
matches the acquired envelope. Binding energies are referenced to
the aliphatic C is line at 284.6 eV.
[0054] In at least one embodiment, the air plasma treatment, at a
certain dosage and in concert with the glass fiber component
included in the substrate, also effectuates the generation of a
mechanical bond between the foam adhesive and the substrate
surface. In at least one embodiment, the mechanical bond is
illustratively formed through a portion of glass fibers otherwise
localized up to 80 microns deep from the surface and become exposed
by the application of the surface treatment. Assuming a
stoichiometric mixture is provided, a GFPP having 50 weight percent
of glass fiber component may be oxidized to yield a surface of
about 45.3 atomic percent of oxygen atoms. When the surface is
completely, at least theoretically, depleted of carbon atoms by
etching, an oxygen content on the surface in an amount of 66.7
atomic percent may result. The 66.7 atomic percent of oxygen atoms
on the surface illustratively represents a situation where the
silicon atoms are substantially oxidized by the etching
process.
[0055] Depending on the glass fiber content and mean fiber length
of a particular substrate, an air plasma treatment at certain
dosage facilitates the beneficial formation of both the chemical
bonds and the mechanical bonds between the substrate and the foam
adhesive. Care should be taken, however, to ensure a proper range
of air plasma intensity with which the substrate surface is
treated. It is discovered that the effect of the air plasma
treatment applicable to the glass fiber filled polypropylene
substrate may be binary in that air plasma treatment at a certain
dosage may actually discount the beneficial enhancement of the bond
strength. While not intended to be limited by any particular
theory, one possible mechanism may be proposed as to why a reduced
amount of oxidized species is identified with certain extended air
plasma treatment. It is known (Walzak M J et al., Journal of
Adhesion Science and Technology, 9(9), 1229-1248, 1995) that
extended surface oxidation results in chain scission reactions and
the formation of low-molecular-weight oxidized materials (LMWOM).
The LMWOM further oxidizes to form carbon dioxide gas. Thus, while
an air plasma treatment at certain dosage induces the formation of
oxidized moieties that remain cross-linked on the substrate
surface, yet additional dosages may over-oxidize the substrate
surface and causes the formation of LMWOM and/or carbon dioxide.
The LMWOM and the carbon dioxide are comparably less cross-linkable
to the substrate surface and are subsequently blown away and
expelled from the surface with high-velocity airflow and direct
surface impingement inherent with the air plasma treatment.
[0056] The effectiveness of the air plasma treatment on enhancing
the bond strength of the GFPP substrate to a foam adhesive varies
as to the mode of operation. Variable aspects of the air plasma
operation mainly include the distance between the plasma beam
nozzle and the substrate surface, the moving rate of the plasma
beam nozzle, and whether the plasma beam rotates or is rather
static. These parameters are chosen in a coherent fashion so as to
bring out the most effective bonding enhancement particular to the
glass fiber filled polypropylene substrate and the foam
adhesive.
[0057] As revealed by the surface topography measurements, air
plasma treatment at a certain low dosage increases surface
roughness of GFPP by a factor of several times; while an increase
in surface roughness by a factor of up to forty (40) times may be
realized when the air plasma treatment is operated at a certain
high dosage. It is generally accepted that the slower the beam
nozzle moves and/or closer the beam nozzle is to a surface, more
intensified the air plasma treatment becomes. For a static
non-rotating plasma beam, one exemplary low dosage air plasma may
be generated when a distance between the beam nozzle and the
substrate surface is kept at a value between 10 to 20 millimeters
and/or the beam nozzle moving speed relative to the surface is
between 300 to 800 millimeters per second. One exemplary high
dosage air plasma may be generated when a distance between the beam
nozzle and the substrate surface is below 5 millimeters and/or the
beam nozzle moving speed relative to the surface is at or below 150
millimeters per second. At a given glass fiber content and subject
to certain limitations as will be elucidated in detail below, the
higher the air plasma dosage, the rougher the substrate surface.
The increase in surface roughness is mainly due to the fact that
more portions of the glass fiber component of the substrate,
otherwise localized up to 80 microns deep from the surface, are
being exposed to the surface by air plasma etching. When presented
with an increase amount of glass fibers being exposed, the
substrate surface is better situated to form mechanical bonds with
a foam adhesive through the exposed glass fiber.
[0058] In at least one embodiment, a rotational non-static beam,
such as a table-top unit, may be used for delivering certain
dosages of air plasma treatment. The unit having a RD-1004 head
with a 2000 rpm rotating 1-inch diameter nozzle is operated at 9.5
amps of current. To effectuate an exemplary low air plasma dosage,
the beam nozzle of the unit may be positioned at a distance of 8
millimeters from the surface at a speed of 83.3 millimeters per
second. To effectuate an exemplary high air plasma dosage, the beam
nozzle of the unit may be positioned at a distance at or below 5
millimeters with a delivery speed at or below 33 millimeter per
second.
[0059] Conventional sanding which, while increasing roughness of a
surface, causes accumulation of unwanted waste from both the
surface material and the sanding tool. As such, the sanding often
results in a layer of physical waste debris that impedes subsequent
bonding. Unlike conventional sanding, the surface treatment such as
the air plasma treatment increases surface roughness by exposing
glass fibers for forming mechanical bonds thereof to the foam
adhesive. As such, the air plasma treatment effectively enhances
surface roughness without having to cause unnecessary physical
waste debris.
[0060] In at least one embodiment, the polymer insert further
includes an outer layer attached to the substrate and in another
embodiment positioned away from the foam adhesive. The outer layer
provides additional structural support. The substrate may be molded
directly onto the outerlayer during construction. An exemplary
outer layer is made of metals illustratively including aluminum,
cast iron, steel, fabrics, wood, bamboo, other thermoplastic or
thermosetting polymers, or any combination thereof.
[0061] Having generally described this invention, a further
understanding can be obtained by reference to certain specific
examples which are provided herein for purposes of illustration
only and are not intended to be limiting unless otherwise
specified.
EXAMPLE 1
[0062] X-Ray Photoelectron Spectroscopy Surface Analysis-Part I
[0063] The glass fiber filled polypropylene specimens (GFPP
specimen) having variable glass fiber content of 10 to 50 weight
percent and with a mean glass fiber length of 3 millimeters are
manufactured to have dimensions of 25 millimeters in width, 3.0
millimeters in thickness, and 100 millimeters in length. The GFPP
specimens are characterized by X-ray photoelectron spectroscopy
before and after an air plasma treatment. Low dosage rotational air
plasma is carried out at a speed of 50 millimeters per second and a
nozzle distance of 6 millimeters. The results are included in Table
1. The base polypropylene polymer specimens with zero percent of
glass fiber content exhibit a surface composition of 99% or greater
in carbon atoms. The air plasma treatment creates a substantial
amount of oxygen, with a concomitant amount of nitrogen generated
possibly from the air plasma source. In addition, silicon is also
observed. Interestingly, the silicon content does not seem to be in
direct proportion, as seen in this example, with respect to weight
percentages of the glass fiber component. It is possible that the
air plasma with the dosage used in this example exposes sub-surface
silicon nano-particles, without yet etching the surface
sufficiently to expose the glass fibers.
TABLE-US-00001 TABLE 1 Surface atomic composition of GFPP specimens
upon air plasma treatment - part I Composition - Atomic Percent
base on % Glass All the Surface Atoms Detected Treatment Fiber
Carbon Oxygen Nitrogen Silicon Others None 10 99.0 1.0 20 99.0 1.0
30 99.7 0.3 40 99.6 0.4 50 99.6 0.4 Air 10 68.1 26.6 1.8 3.3 0.4
Plasma 20 65.1 28.0 1.4 5.0 0.9 30 77.6 19.8 1.8 0.4 0.6 40 74.1
23.3 2.7 50 83.5 14.8 1.7
[0064] Blanks in Table 1 indicate that relevant test parameters are
below detectable range.
[0065] It should be noted, from the Table 1 shown above, that a
reduction in surface carbon content and an concurrent increase in
surface oxygen content is consistently observed amongst the various
GFPP specimens tested. As such it can be reasonably concluded that
the GFPP specimens respond fairly similarly to a given air plasma
treatment within a relatively broad glass fiber loading range, for
example, from 10 to 50 weight percent.
[0066] FIG. 1A shows XPS survey spectra acquired from the GFPP
specimens reported in Table 1 above. The spectra reveal the
evolution of oxygen and nitrogen on the surface as a result of the
air plasma treatment. The details of oxygen incorporation are shown
in the XPS C is core level spectra of FIG. 2A. The initial spectrum
contains a single peak at 284.6 eV, attributed to the olefinic
carbon. After the air plasma treatment, additional peaks appear as
the oxidized carbon species such as ether, hydroxyl, ketone, and
carboxyl (FIG. 2B).
EXAMPLE 2
[0067] X-Ray Photoelectron Spectroscopy Surface Analysis-Part
II
[0068] Surface composition investigation is further carried out
with respect to those GFPP specimens having a narrower range of
glass fiber content and under additional experimental variations.
The GFPP specimens are prepared by the same method set forth in the
Example 1 above. In addition, the GFPP specimens are categorized
with respect to glass fiber content (0, 20, or 30 weight percent),
mean fiber glass length (1 millimeter verses 3 millimeters), and
air plasma dosage (dosage "a" verses "b"). Surface atomic
compositions, reported as atomic percent of all the atoms detected
on a GFPP specimen surface, are reported in Table 2. Again, it is
observed that all specimens without air plasma treatment have a
surface composition essentially of carbon atoms.
TABLE-US-00002 TABLE 2 --Surface atomic composition of GFPP test
specimens upon air plasma treatment - part II Mean Fiber Glass
Fiber Elemental Composition - Air Plasma Length Content Atomic
Percent O/N Specimen Treatment (millimeter) (wt %) C O N Si Other
Ratio "000PP-0" None n/a 0 99.1 0.9 "S20GFPP-0" 1 20 99.3 0.7
"S30GFPP-0" 30 99.3 0.8 "L20GFPP-0" 3 20 99.5 0.5 "L30GFPP-0" 30
99.8 0.2 "000PP-a" Air Plasma n/a 0 62.8 32.8 4.4 0.2 7.5
"S20GFPP-a" Dosage "a" 1 20 70.4 26.7 3.3 0.1 8.2 "S30GFPP-a" 30
65.9 30.4 3.5 8.6 "L20GFPP-a" 3 20 75.3 21.3 2.4 0.8 8.9
"L30GFPP-a" 30 67.4 27.2 2.0 2.5 1.0 13.7 "000PP-b" Air Plasma n/a
0 72.0 25.0 3.1 8.1 "S20GFPP-b" Dosage "b" 1 20 73.6 23.8 2.3 0.3
10.2 "S30GFPP-b" 30 73.3 23.7 1.7 0.9 14.2 "L20GFPP-b" 3 20 75.3
21.3 2.4 0.8 8.9 "L30GFPP-b" 30 67.4 27.2 2.0 2.5 1.0 13.7
[0069] Blanks in Table 2 indicate that relevant test parameters are
below detectable range.
[0070] The rotational treatment for air plasma dosage "a" is moved
at a speed of about 83 millimeters per second while a static
non-rotating plasma beam moving at 150 millimeters per second is
used for dosage "b". As defined previously, a rotational plasma
beam, in general, delivers a much lower plasma intensity when
compared to a static non-rotating plasma beam. As designed herein,
the dosage "a" is characterized as a lower dosage in air plasma
intensity when compared to the dosage "b". Both the "a" and the "b"
dosages of the air plasma treatments create a substantial amount of
oxygen, with a concomitant amount of nitrogen generated from the
air plasma source. With the dosage "a" treatment, oxygen uptake is
26.7 to 32.8%, with 3.3 to 4.4% of nitrogen. The oxygen/nitrogen
ratio measured on the surface is around 8 or 9, just over double
the composition ratio of the air source used to generate the
plasma, which is 3.7 (78.1/20.9). Interestingly, the amount oxygen
and nitrogen incorporated at the dosage "b" is actually about 20%
less than that observed at the lower dosage. As such, it is
observed that certain air plasma dosages, such as the dosage "b"
here, may retard the extent of oxidative state of the specimen
surfaces.
[0071] XPS high resolution C 1s core level spectra is again
employed to determine the chemical state of carbon after each
treatment. FIG. 3 shows overlaid C is core level spectra of the 30%
GFPP specimens with mean fiber length of 3 millimeters reported in
Table 2 above. The spectrum acquired from the L30GFPP specimens
shows a single peak at 284.6 eV identified as aliphatic carbon (A).
After the low dosage air plasma treatment, additional peaks are
observed with the L30GFPP-a specimens at binding energies of 286.2
eV, 287.4 eV, and 288.7 eV, identified as ether/hydroxyl (B),
ketone (C), and carboxylate (D) chemical states, respectively.
While still being significantly greater than those observed without
the L30GFPP-0 specimens that are without any air plasma treatment,
the amount of oxidized carbon species detected from the L30GFPP-b
specimens are relatively lower than those with the L30GFPP-a
specimens.
EXAMPLE 3
[0072] Surface Topography Analysis
[0073] Optical profilometry is performed on various GFPP specimens
to determine to what extent surfaces of the GFPP specimens are
physically affected by an air plasma treatment. The topography is
measured at 20.times. and 100.times. magnification to examine the
roughness at different length scale. The 20.times. magnification
measurements reveal structures between base polypropylene polymer
and the glass fibers, whereas the 100.times. magnification measures
more detailed structures among the glass fibers of the
specimens.
[0074] Roughness measurements are presented in terms of Rq,
root-mean square deviation from center where,
Rq = 1 n i - 1 n ( Z i - z _ ) 2 ( 1 ) ##EQU00001##
[0075] n is the number of data points; z is the deviation from the
center of the surface plane, z. For 100.times. magnification,
n=353,280 (736.times.480) and the point resolution is 79.9 nm. For
20.times. magnification, n=1,300,993 (1232.times.1056) and the
point resolution is 811 nm. The effect sample tilt is removed from
all presented data and calculations.
[0076] The 20.times. magnification topography measurements within
lmm.sup.2 (square millimeter) area of the specimens reported in
Example 2 above is presented in FIG. 4. Measurements at the
20.times. magnification include the topography introduced by the
imbedded glass fibers. Each Rq value in the unit of micrometer
(.mu.m) is reported in average of three measurements with error
bars representing one standard deviation. Within the specimens
tested, there is no statistically significant differences in Rq
between the untreated specimens and the specimens exposed to the
dosage "a" air plasma treatment, with values of Rq all under 2
However, there is an observable trend of average roughness
increasing with fiber length (1 to 3 millimeters) and also with
glass fiber content (20 to 30%). In contrast, surface roughness of
the GFPP specimens increases dramatically, for example, by more
than 30 times, after the dosage "b" air plasma treatment. Also,
there is an observable trend of average roughness increasing with
fiber length (1 to 3 millimeters) and also with glass fiber content
(20 to 30%).
[0077] The change in surface reflectivity of the specimens reported
in Table 2 above is represented in the optical micrographs as shown
in FIG. 5. FIGS. 5a-5c depict the optical micrographs relevant to
the S30GFPP-0 specimens, the S30GFPP-a specimens, and the S30GFPP-b
specimens, respectively. FIGS. 5d-5f depict the optical micrographs
relevant to the L30GFPP-0 specimens, the L30GFPP-a specimens, and
the L30GFPP-b specimens, respectively.
[0078] The 100.times. magnification topography measurements within
a smaller area of 44.7 .mu.m (micrometers).times.58.8 .mu.m
(micrometers) of the specimens reported in Example 2 above is
presented in FIG. 6. The longer wavelength waviness previously
observed with the larger area (1 mm.times.1 mm) is effectively
filtered out at the 100.times. magnification. Each Rq value in the
unit of nanometer (nm) is reported in average of 10 measurements
with error bars representing one standard deviation. The data
reported with the 100.times. magnification shows a trend of changes
that is very similar to the date reported with the 20.times.
magnification shown in FIG. 4. However, Rq values measurable with
the 100.times. magnification are considerably lower than those
measurable with the 20.times. magnification as shown in FIG. 4,
partly because the smaller area of 44.7 .mu.m.times.58.8 .mu.m
measured under the 100.times. magnification substantially excludes
the inclusion of glass fibers and represents rather the waviness of
the polypropylene resin itself.
[0079] Impact of the air plasma treatment towards surface roughness
of the L30GFPP specimens reported in Table 2 above is further
represented by 3-dimensional plots shown in FIG. 7, in 20.times. or
100.times. magnification. The 3-D profiles of both the untreated
and low-dose treated samples confirm that there is little
difference in the surface appearance at either magnification. At
the 20.times. magnifications, it is observed that the dosage "b"
air plasma treatment has induced the exposure of glass fibers of
the specimens. The profile of the specimens after the dosage "b"
air plasma treatment, as shown in the 100.times. magnification
image, also shows a change in appearance. The surface may have
melted and reformed due to high temperatures encountered during the
dosage "b" air plasma treatment.
EXAMPLE 4
[0080] Adhesion Testing
[0081] The bond strength is recorded in the unit convention of psi
and measured by a lapshear test. The lap shear determines the shear
strength of adhesion between the substrate and the foam adhesive.
The GFPP test specimens are placed in the grips of a testing
machine and pulled at a rate about 5 millimeters per minute until
failure occurs.
[0082] Exposure of glass fibers presents mechanical bonds for a
foam adhesive to bond to; yet certain high air plasma dosage, as
reported in Example 3 above, may reduce the amount of the oxidized
carbon species. As such, an experiment is designed to elucidate how
an overall adhesion characteristic of the GFPP specimens may be
affected by factors of plasma dosage, glass fiber content, and
glass fiber length.
[0083] FIG. 8 shows the distribution of adhesive bond strengths
measured from the 000PP-0 specimens, the 000PP-a specimens, and the
000PP-b specimens reported in Table 2 above. Bond strength is
measure through lapshear test and five lapshear measurements are
made for each test condition. The mean bond strength (215 psi) of
the 000PP-a specimens increases slightly from 190 psi for the
000PP-0 specimens. With a higher dosage treatment of the dosage
"b", the mean bond strength of the 000PP-b specimens is observed to
have decreased from 190 to 157 psi, or 21.0%. The mode of adhesion
failure for the same set of specimens is reported in FIG. 9. As
shown in FIG. 9, only 10 to 14% cohesive failure is similarly
observed across the specimens.
[0084] Similar lapshear testings are also conducted on the
L30GFPP-0 specimens, the L30GFPP-a specimens, and the L30GFPP-b
specimens reported in Table 2 above. The lapshear results of those
specimens are given in FIGS. 10 and 11. Firstly, a 21.1% increase
in bond strength, from 190 to 230 psi, is noted in the GFPP
specimens by the mere inclusion of 30 weight percent of glass fiber
component. This is likely the result of the substantial 3-5 fold
increase in surface roughness for the glass-filled materials, as
noted in the topography data of FIG. 4. The bond strength of the
L30GFPP-a specimens that have been treated with the dosage "a"
plasma treatment is further increased from 230 to 410 psi, or
78.3%. This 78.3% increase is at least five times the bond strength
increase of 13.2% seen with the 000PP-a specimens reported in FIG.
8. In addition, the majority (mean of 87.4%) of the L30GFPP-a
specimen lapshear fail cohesively (FIG. 11). Furthermore, in
contrast to the 000PP-b specimens of FIGS. 8-9 where the dosage "b"
air plasma treatment is shown to decrease bond strength as compared
to the 000PP-0, the L30GFPP-b specimens elicit improved adhesion
from 230 psi of without air plasma to 285 of the dosage "b" air
plasma, or an increase of 23.9%. Albeit a reduced improvement
compared to bond strength improvement with the dosage "a" air
plasma, the 23.9% increase in bond strength elicited by the dosage
"b" plasma on the L30GFPP-b specimens demonstrates that the
inclusion of the glass fiber component in the GFPP specimens
effectively compensates any adhesion loss elicited by a high dosage
such as the dosage "b" air plasma. While not intended to be limited
by any theory, one explanation is at least a portion of the glass
fiber component is being exposed to the GFPP specimen surface by
the air plasma treatment and presenting a mechanical linkage with
the foam adhesive. This mechanical linkage or bond is simply not
realized in the pure polypropylene specimens where no glass fiber
component is present.
[0085] The same lapshear data from FIGS. 10 and 11 are
alternatively presented in FIGS. 12 and 13 and the data is sorted
by glass fiber length and content. The data shows patterns of
changes based on dosages of air plasma treatment and substrate
glass fiber content. As shown in the FIGS. 12 and 13, poorer
adhesion is noticed with the L20GFPP-0 specimens and comparably
better adhesion occurs with the L30GFPP-a specimens. In fact, this
is the only specimen that exhibits 100% cohesive failure for all
five coupons tested (FIG. 12). Although in general there is
considerable variation in the data, it is still quite clear that
better adhesion is realized with the specimens with higher glass
fiber content.
[0086] The same data of FIGS. 12 and 13 are further alternatively
represented by main effects plots depicted in FIGS. 14 and 15. It
is demonstrated that air plasma dosage delivers the most
significant impact, as compared to glass fiber content and mean
glass fiber length, on adhesion with respect to both bond strength
and failure mode. Low-dosage air plasma treatment imparts a
dramatic increase in adhesion and the high plasma dosage treatment
increases overall adhesion yet possibly with a lesser extent.
[0087] The same bond strength data for the shorter fiber specimen
group (collectively including S20GFPP-0, S30GFPP-0, S20GFPP-a,
S30GFPP-a, S20GFPP-b, and S30GFPP-b) verse the longer fiber
specimen group (collectively including L20GFPP-0, L30GFPP-0,
L20GFPP-a, L30GFPP-a, L20GFPP-b, and L30GFPP-b) is further
represented by boxplots in FIG. 16. A two-sample T-test is run on
this data and it is demonstrated that the longer fiber specimen
group appears to exhibit better adhesion than the shorter fiber
specimen group with a 95% confidence of a statistical difference in
data means between the groups.
[0088] Table 3 alternatively demonstrates differential bond
strength results of FIG. 13 in response to the three test
variables, namely air plasma dosage, mean fiber length, and glass
fiber content. The bond strength enhancing effect of each variable
is quantified and reported in Table 3. Between the pure
polypropylene specimens with zero glass fiber content, the air
plasma treatment at dosage "a" increase the lapshear bond strength
by 25 psi from 190 (of the 000PP-0 specimens) to 215 psi (of the
000PP-a specimens), or an increase of 13.1%. A bond strength mean
for the GFPP specimen group with no air plasma treatment
(collectively including S20GFPP-0, S30GFPP-0, L20GFPP-0, and
L30GFPP-0) is calculated to be 230 psi; a bond strength mean for
the GFPP specimen group with dosage "a" air plasma treatment
(collectively including S20GFPP-a, S30GFPP-a, L20GFPP-a, and
L30GFPP-a) is 410 psi; and a bond strength mean for the GFPP
specimen group with dosage "b" air plasma treatment (collectively
including S20GFPP-b, S30GFPP-b, L20GFPP-b, and L30GFPP-b) is 285
psi. As such, the dosage "a" air plasma treatment elicits a bond
strength enhancing effect with a change of 180 psi or 78.2%
increase from the non-treated counterpart of 230 psi. The mere
inclusion of glass fibers in the GFPP specimens greatly
substantiates the impact of the air plasma treatment from rendering
an increase of 13.1% to 78.2%, or an almost 6-fold. Upon the higher
dosage "b" air plasma treatment, the mean bond strength of the pure
polypropylene specimens is reduced by 33 psi while an increase of
55 psi is rather observed with the corresponding dosage "b" GFPP
specimen group. In addition, the lower 20% (weight percent) glass
fiber specimen group (collectively including S20GFPP-0, S20GFPP-a,
S20GFPP-b, L20GFPP-0, L20GFPP-a, and L20GFPP-b) has a bond strength
mean of 276 while the higher 30% (weight percent) glass fiber
specimen group (collectively including S30GFPP-0, S30GFPP-a,
S30GFPP-b, L30GFPP-0, L30GFPP-a, and L30GFPP-b) has a bond strength
mean of 340. Furthermore, the shorter and longer fiber specimen
groups as defined above have a bond strength mean of 293 psi and
323 psi, respectively. As such, a bond strength increase in the
amount of 64 psi is observed with a fiber content change from 20%
to 30% and an amount of 30 psi is observed with a mean fiber length
change from 1 to 3 millimeters. It is therefore reasonably
concluded that amongst the three tested variables, the air plasma
treatment is the most significant contributor in enhancing the bond
strength of the specimens tested here.
[0089] Change in lapshear bond strength in response to various
testing conditions
TABLE-US-00003 Change in Lapshear Bond Strength (psi) Pure
Polypropylene Specimens Improvement None Dosage "a" Dosage "b" a b
Air Plasma 190 215 157 25 -33 Glass Fiber Filled Polypropylene
Specimens Improvement None Dosage "a" Dosage "b" a b Air Plasma 230
410 285 180 55 20% 30% Improvement Glass Fiber Content 276 340 64 1
millimeter 3 millimeters Improvement Glass Fiber Length 293 323
30
[0090] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that
various changes may be made without departing from the spirit and
scope of the invention. Additionally, the features of various
implementing embodiments may be combined to form further
embodiments of the invention.
* * * * *