This document describes a new palladium-free surface activation process for nickel electroless plating on ABS plastic. The process involves immobilizing nickel nanoparticles on the ABS surface as catalyst sites. The ABS surface is first etched to introduce hydrophilic functional groups like sulfonic acid. It is then treated with chitosan which reacts with these groups. Soaking the surface in a nickel sulfate solution deposits nickel nanoparticles which are reduced to elemental nickel. This nickel-activated surface allows for uniform electroless deposition of a smooth, amorphous nickel-phosphorus layer without using expensive palladium. XPS, SEM and XRD characterization show the introduction of functional groups, uniform deposition of nickel nanoparticles, and amorphous nature of the

1. Materials Letters 63 (2009) 840–842
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Materials Letters
journal homepage: www.elsevier.com/locate/matlet
A new palladium-free surface activation process for Ni electroless plating on
ABS plastic
Xuejiao Tang ⁎, Chengliang Bi, Changxiu Han, Baogui Zhang
College of Environmental Science & Engineering, Nankai University, Tianjin, 300071, PR China
a r t i c l e i n f o a b s t r a c t
Article history:
Received 26 June 2008
Accepted 6 January 2009
Available online 10 January 2009
Keywords:
Palladium-free
Surface activation
Nanoparticle
Nickel deposition
XPS
SEM
XRD
A novel palladium-free and environmentally friendly surface activation process for Ni electroless plating was
studied. The activation was carried out by immobilizing Ni nanoparticles as catalyst site on the ABS plastic
surface. It is a cost effective activation method since Ni nanoparticles were successfully used as catalyst. The
surface of ABS foils after etching and activating was investigated by XPS to get more information about the
interfacial reaction mechanisms. Ni nanoparticles were uniformly formed on the substrate and a glossy
and smooth Ni–P plating layer was obtained according to the SEM photographs. XRD pattern showed that the
Ni–P layer is amorphous.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
ABS plastic is an important engineering material for its high
thermal stability, excellent mechanical strength, and high resistance
to chemical reagents. However, its application is limited because it is
non-conducting and easily fretted. Metallized ABS can be widely used
in many fields since its outstanding properties of engineering plastic
and metal. For many years, activation process for metallization of non-conducting
substrates has attracted increasing attention [1–4].
In the conventional activation processes, noble metal palladium
is usually employed as the catalyst sites to initiate the electroless
plating [5–8]. The cost of the palladium has increased in recent years,
which makes the electroless plating method rise in price. Thus, it is
very important to develop a cost effective activation techniques. Some
other less expensive metals, such as Cu and Ni, have the catalytic
property for electroless plating. It is reported that Cu deposition was
achieved by laser-induced chemical liquid-phase deposition (LCLD)
method [9,10]. In this method, Cu(0) seeds was formed on the sub-strate
by a variety of laser radiations and then initiated the sequential
Cu electroless deposition. Seita et al. [11] developed a chemical pro-cess
that consists of adsorbing the Cu(+2) species onto the sulfonated
surface from a cupric aqueous solution and reducing Cu(0) by NaBH4
solution. It is so promising if nickel can be successfully used as catalyst
sites for nickel deposition in the same way. To our knowledge, direct
Ni metallization has been mentioned in the literature [12,13], but
expensive equipment and complex operations are required.
This work studied on the activation process of immobilizing Ni
nanoparticles on the ABS substrate as catalyst site by biopolymer for
nickel electroless plating. The components on the substrate surface
after etching and activating were investigated by X-ray photoelectron
spectroscopy (XPS), and the interfacial reaction mechanisms are dis-cussed.
It was found that an extra and important hydrophilic func-tional
group (H–O–S (O2)–C6H4)– was introduced during the etching
process by comparison with our previous work [4]. The appearances of
the activated surface on ABS and deposited Ni–P layer are character-ized
by Scanning Electron Microscopy (SEM) and the Ni–P layer was
also characterized by X-ray diffraction (XRD).
2. Materials and methods
2.1. Materials
Chitosan (CTS, Deacetyl Degree ~92%) was purchased as industrial
grade power from Xiamen Sanland Chemical Agent Ltd. All the latter
chemicals used were of analytical grade purity.
2.2. Methods
2.2.1. Etching and activating
The etching was performed with the method mentioned in the
literature [4].
After etching, the foils were dipped into 1% acetic acid solution
containing 15 g/L CTS for 5 min at room temperature, and then dried
⁎ Corresponding author. Tel.: +86 22 23503592; fax: +86 22 23508807.
E-mail addresses: jiaojiaosnow@163.com, tangxuejiao@mail.nankai.edu.cn (X. Tang),
bichengliang@mail.nankai.edu.cn (C. Bi), hanchangxiu@mail.nankai.edu.cn (C. Han),
bgzhang316@eyou.com (B. Zhang).
0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.matlet.2009.01.006

2. X. Tang et al. / Materials Letters 63 (2009) 840–842 841
at 60 °C for 15 min. Afterward, the foils (ABS–CTS for short) were
immersed in a nickel sulfate solution (NiSO4∙6H2O: 2.0 g/L) at 40 °C for
10 min, rinsed and then reduced in a solution of KBH4 (3.0 g/L) at 40 °C
for 5 min. ABS–CTS–Ni was obtained.
The electroless nickel deposition was catalytically achieved by
dipping the pre-nucleated substrates (ABS–CTS–Ni) into a solution
containing sodium citrate as complexing agent and sodium hypopho-sphite
as reducing agent at 40 °C for 20 min.
2.2.2. Surface characterization
The chemical compositions and reactions on the substrate surface
after each treatment step were characterized by XPS. XPS spectra were
recorded using a Kratos Axis Ultra DLD spectrometer (UK) and em-ploying
a monochromated Al-Ka X-ray source (hv=1486.6 eV), hybrid
(magnetic/electrostatic) optics, and amulti-channel plate and delay line
detector.
The appearanceswere characterized by SEM. Electron micrographs
were taken by a SHIMADZU SS-550 scanning electron microscope (JP).
The XRD measurement of the deposited Ni–P layer was made with
Rigaku D/max-2500 powder diffractometer using CuKα radiation.
3. Results and discussion
The XPS investigations of ABS and ABS–CTS–Ni were undertaken. The XPS data are
listed in Table 1.
Our previous research has reported [4] that new hydrophilic functional groups
(–OH and/or –COOH) are formed on the ABS substrate surface after etching, and that
newchemically-stable functional groups –C(O)–NH–, –C(O)–O– and –C–O–C– formed
through the reaction of –OH and –NH3 of the CTS filmwith the hydrophilic functional
groups –OH and/or –COOH on the surface of ABS after the CTS filmwas dried at 60 °C.
This greatly enhanced the adhesive strength of the CTS film and ABS substrate surface.
Furthermore, ongoing research found that another important hydrophilic func-tional
group (H–O–S (O2)–C6H4)– was formed after etching. As shown in Table 1, the
S2p3/2 photoelectron spectrum peak appears at a binding energy of 168.7 eV for ABS,
which corresponded to the peak position of H–O–S (O2)–C6H4–, different from those of
NiSO4 and H2SO4. The sulfonic acid group was introduced by an electrophilic aromatic
substitution reaction of the benzene ring of the ABS during the etching with sulfuric
acid solution. Drying the CTS film on the surface of ABS at 60 °C causes the reaction of
the sulfonic acid group with the CTS amino groups (–NH3) forming new chemically-stable
–NH–S (O2)–C6H4– (the S2p3/2 absorption peak appears at a binding energy of
167.6 eV for ABS–CTS–Ni, in Table 1) functional groups. It illuminates that the etching
process can modify the surface to be hydrophilic, as well as enhance the adhesive
strength of CTS film and ABS substrate by reaction of functional groups.
The N1s spectrum absorption peak of ABS–CTS–Ni (407.5 eV) shifted 8.3 eV higher
compared to that of –NH3 in CTS (399.2 eV). This result indicates that nickel had chelated
with the nitrogen atom's isolated electrons, causing the thickness of the electron clouds
around nitrogen atoms to decrease and consequently shift the binding energy higher
[4,18]. Thus, Ni is immobilized on CTS film with higher adhesive strength by chemical
adsorption.
In Table 1, two Ni species peaks of Ni2p3/2 appears in XPS data for ABS–CTS–Ni. The
right peak (at binding energy of 852.8 eV) corresponds to Ni2p3/2 peak of Ni, and the left
peak (at binding energy of 857.8 eV) corresponds to Ni2p3/2 peak of NiSO4. The results
indicate that Ni(0) had successfully formed on ABS–CTS–Ni after being reduced by KBH4
solution.
The SEM photograph of ABS–CTS–Ni was showed in Fig. 1. The Ni nanoparticle
(diameterb50 nm) was uniformly formed on the substrate. It was firmly verified that
the formed Ni nanoparticle could be sufficient to start the nickel electroless plating.
Nickel deposition was achieved by dipping ABS–CTS–Ni into the electroless solution.
The plating player appeared glossy and smooth as showed in Fig. 2. The thickness of the
Ni–P layer is 7.2 μm on average determined by weight method. Fig. 3 shows the XRD
pattern of Ni–P plating layer produced with the described pretreatment method. A
broad diffraction peak in Fig. 3 is observed at around 45°, which originates from the
electrolessly deposited Ni–P layers. The results of XRD analyses clearly revealed that the
deposited Ni–P layer is an amorphous state. The amorphous state of the Ni–P layers is
largely attributed to the distortion of crystalline lattice of Ni caused by P atoms [19,20].
4. Summary
A novel palladium-free surface activation process for Ni electroless
plating on ABS had been achieved. This activation process was carried
out by immobilizing Ni nanoparticles as catalyst on ABS substrate. It
was found that an extra and important hydrophilic functional group
(H–O–S (O2)–C6H4)– was introduced during the etching process by
comparison with our previous work. It was confirmed that the formed
Table 1
XPS data for Ni, NiSO4, H2SO4, CTS, ABS and ABS-CTS-Ni (eV)
Samples N1s S2p3/2 Ni2p3/2
Ni – – 852.8 [14]
NiSO4 – 169.2 [15] 857.3 [16]
H2SO4 – 169.6 [17] –
CTS [13] 399.2 – –
ABS 399.3 168.7 –
ABS–CTS–Ni 399.1 407.5 167.6 852.8 857.8
Fig. 1. SEM photograph of ABS–CTS–Ni.
Fig. 2. SEM photograph of Ni–P layer.
Fig. 3. XRD pattern of electroless deposition Ni–P layer.

3. 842 X. Tang et al. / Materials Letters 63 (2009) 840–842
Ni nanoparticles was sufficient as catalyst for nickel electroless
plating. A glossy and smooth Ni–P plating layer was obtained from
an electroless nickel plating bath using this activation method. This
environmentally friendly activation process holds promise to reduce
both capital and operational costs in large scale manufacturing.
Acknowledgement
The authors gratefully acknowledge financial support by the program
(05YFSYSF030) from the Tianjin municipal science and technology
committee.
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