Introduction
Metals and alloys are considered as tough and resilient materials to fabrication of Structures, Components for Vehicles, engines, furniture, refrigerator etc. [1]. Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulphide. It occurs when the metal comes in contact with air (oxygen), water (moisture) or acids during its lifetime. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. This hampers the mechanical properties of the metals making them inefficient for use leading to huge losses.
Need to prevent corrosion in automobiles
Corrosion is the enemy of all automobiles. It makes protecting the cars against corrosion vital for value retention, safety, customer satisfaction and ultimately the image of the company. This protection must begin from a very early stage, as early as manufacturing of the smallest metal part required in the vehicle. The various traditional methods are now replaced with easy to use, new generation VCI packaging made of plastic or paper.
New technologies to prevent corrosion of automobile parts and other metals
Carboxylic and heterocyclic rings offer the adsorption of organic inhibitors on metal substrates [2-4]. It can serve as a guard for several metals like Iron, Zinc, Aluminum, Silver, Copper etc. and their alloys. VCI is the common term for “Volatile Corrosion Inhibitor,” “Vapour Corrosion Inhibitor,” or “Vapour Phase Corrosion Inhibitor,” a revolutionary technology that simplifies corrosion protection and is ideal for keeping enclosed void spaces (e.g., packages, equipment internals, or structural metal cavities) rust-free by chemical volatilization at room temperature to form a thin deposition layer on the nearby surfaces. This is an ideal solution for automobiles as the various metal parts (small or big) used in an automobile are sourced from different locations and assembled on a single assembly line. Protection to the automotive components is needed during transit as well as storage before it is taken up for assembling. At NICHEM, we have developed an excellent range of VCI Packaging Additives to serve the purpose and we keep on improving the technologies for better and better. These additives can be used in different forms such as in packaging film, laminate, desiccant, pouches, foam, liners, emitters, diffusers, craft paper etc.
Performance Testing of VCI
The VCI product performance can be analyzed by industry accepted standards namely German APL TL 8135-002 (German Military Test) [5], ASTM B117 (Salt Spray Test)[6], Razor Blade Test, Humid cyclic Test and Climate Stress Test [7]. At NICHEM, we have developed various grades of VCI Additives which provide MS as well as multi-metal protection and comply to these international standards. One of our customers sent an enquiry for VW 51064 compliant VCI product. VW 50164 is known as one of the most stringent test standards followed by the automobile industry for VCI packaging. Considering the growing demand by our customers, we developed a suitable grade of VCI Additive to comply with VW51064.
Materials & Methods
About VW51064 Test Standard
The VW 51064 Test Standard demonstrates severity and longevity of compliance of the final product in the corrosion prevention of metals. It consists of 3 types of tests – K (Jar Test), KON (Humid Cycle Test) and KDW (Preserving Jar Test). Each test has its own significance and corrosion environment for evaluation purpose. Table 1 below depicts the types of tests described in the standard.
Table 1 – Types of Tests of VW 51064 VCI Test Standard
| Sr No | Test Name | Test Set Up | Test Description |
|---|---|---|---|
|
1 |
K Test
(Jar Test)
|
 a) Rubber bung, |
|
|
2 |
KON Test (Humid Cycle Test) |
 |
|
|
3 |
KDW Test (Preserving Jar Test) |
 |
|
Preparation of the Test Set Up for VW 51064 Standard
We studied the VW 51064 Test Standard and developed the required test set up for each test in-house to check the initial performance in our laboratory as per the standard. This was conducted as a proof of principle study to check which grade of our VCI Additives passes the test.
Preparation of the VCI Films for the Test
We optimized our ResiCor 006 Additive with proprietary additives to make ResiCor 006 VCI-OS and extruded LDPE films at an active concentration of 14,000 ppm in our application lab for the testing as per the 3 tests – K, KON & KDW.
Results & Discussion
ResiCor 006 VCI-OS Film Analysis:
ResiCor 006 VCI-OS Films along with the Control were analyzed for their physical properties such as tensile strength and percentage elongation by ASTM D 882 Standard. A film of size 100 x 25x 0.05 mm was drawn and tested. The VCI-OS Film showed slight deflection in tensile strength and percentile elongation as compared to the Control Film. The desired properties can be standardized by addition of low MFI LDPE during film processing.
Performance testing:
ResiCor 006 VCI-OS Films along with the Control were graded for their performance as per the recommended scale in VW 50164 Test Standard.
Fig 1: Rating Scale of K test
Fig 2: K Test Results of ResiCor 006 VCI-OS and Control Film
Table 2 – Rust grade rating scale of VW 50164 Standard
| Rust Grade (RN) | Definition |
|---|---|
|
|
No Corrosion
|
|
1 |
No Corrosion spots less than <1 mm diameter |
|
2 |
Slight corrosion: <1% of the surface |
|
3 |
Moderate corrosion: 1-5% of the surface |
|
4 |
Heavy corrosion: 5-10% of the surface |
|
5 |
Very high corrosion: >10% of the surface |
The VCI-OS Film showed excellent resistance to humid climatic cycles. It passed the test with RN 1 rating which depicts good corrosion protection as seen in Fig 3 below.
Fig 3: KON Test – ResiCor 006 VCI-OS Film before and after 30 cycles
Table 3 – Rating Scale of VCI Corrosion Protection Effect
| Level | Level Protection factor (SF)* for VCI film Rating | Rating |
|---|---|---|
|
|
≤3,0 |
Negligible |
|
1 |
≤3,5 |
Weak |
|
2 |
≤4,5 |
Moderate |
|
3 |
>4,5 |
Good |
|
*Protection factor (SF) = Number of cycles for ResiCor 006 VCI-OS Film
Number of cycles for Control Film
|
||
The VCI-OS Film passed this most critical test with RN 1 rating which assures high performance of corrosion prevention during the transit. It shows a protection factor SF of more than 5 which ensures good corrosion resistance to the packed metal sample as seen in Fig 4 below.
Fig. 4: KDW Test – ResiCor 006 VCI-OS film before and after 45 cycles
The proprietary additives helped to elevate the performance of ResiCor 006 VCI-OS Film. There was no change in the diffusibility of VCI vapors from the film. VCI-OS films were able to comply to all the 3 tests – K, KON and KDW as summarized in Table 4.
Table 4 – ResiCor 006 VCI-OS Film VW 50164Test Results
| VW 50164 Test type | SF | Performance of VCI-OS Film |
|---|---|---|
|
K-Test |
Not applicable |
Good corrosion Protection (Level 3) |
|
KON Test |
≥4,5 |
Good corrosion Protection |
|
KDW Test |
≤5,5 |
Good corrosion Protection |
Conclusion:
ResiCor 006 VCI-OS Film complied to the in-house testing as per the VW 15064 Automobile Test Standard. The unique combination of actives gave a controlled and stabilized atmosphere to the polymer film which resulted into good corrosion protection rating in all the respective tests. This study indicates that the VCI-OS film can be successfully used in metal packaging applications during transportation and can withstand stringent climatic stresses such as temperature and humidity ranges to 25-55°C and RH 90-98% respectively. It does not release any harmful vapors into the atmosphere and is safe to use. With ResiCor 006 VCI-OS Films, we can ensure metal protection for a longer duration as desired by the automobile industry.
References:
[1] Hyun-Min Yang, Role of Organic and Eco-Friendly Inhibitors on the Corrosion Mitigation of Steel in Acidic Environments— A State-of-Art Review, Molecules 2021, 1.
[2] N. Anusuya, J. Saranya, P. Sounthari, A. Zarrouk and S. Chitra, “Corrosion inhibition and adsorption behaviour of some bis-pyrimidine derivatives on mild steel in acidic medium”, J. Mol. Liq., 2017, 225, 406–417.
[3] C. Verma, L.O. Olasunkanmi, E.E. Ebenso, M. Quraishi and I. Obot, “Adsorption behaviour of glucosamine-based, pyrimidine-fused heterocycles as green corrosion inhibitors for mild steel: experimental and theoretical studies”, J. Phys. Chem. C, 2016, 120, 11598–11611.
[4] C.B. Verma, M. Quraishi and A. Singh, “2-Aminobenzene-1,3-dicarbonitriles as green corrosion inhibitor for mild steel in 1 M HCl: Electrochemical, thermodynamic, surface and quantum chemical investigation”, J. Taiwan Inst. Chem. Eng., 2015, 49, 229–239.
[5] Nelson cheng, Ascertaining the Effectiveness of VCI Anti-Corrosion Properties Of Vappro VCI Inhibicard Coated with Vappro MBL2200 Using German Test Method TL 8135-002, research gate,2016.
[6] S.B. Valdez, rapid method for corrosion protection determination of vci film, Anti-Corrosion Methods and Materials 53/6 (2006) 362–366
[7] L-M Rymer, Operating principle of volatile corrosion inhibitors in the jar test, IOP Conf. Series: Materials Science and Engineering 480 (2019) 012028
