I did a pretty extensive search for the use of grapeseed oil in relevance to hair and unfortunately I came up blank.
I have found out that grapeseed oil has been used previously as a carrier oil in aromatherapy formulations to treat hair loss but was not effective on its own (Archives of Dermatology,pg 602-603, 1999).
It has also been used as a hand cleansing agent so may also cleanse when applied to hair (Contact Dermatitis, pg 208. 1992). I was pretty disappointed in this, it looks like it is a case of science needing to catch up.
I was expecting jojoba oil to have been researched more given its widespread use in hair products and indeed this was the case
1. Jojoba oil does not penetrate into the cortex of hair (Journal of Cosmetic Science, pg 299, 2005). This means it is not a moisturising oil like coconut oil but as it stays on the cuticle, it would be a good sealant
2. Jojoba oil in products gives the feeling of softness ( Journal of the Society of Cosmetic Chemists, pg 635-654,1971).
3. Jojoba oil is part of a formulation to mimic human sebum (natural hair oil) . This may be because it is actually a liquid wax (International Journal of Cosmetic Science, pg 21-25, 2009). This result also supports no.1.
4. An interesting though non natural piece of research - Adding jojoba oil to a hair relaxer helps to stop the hair from breaking (Journal of Cosmetic Dermatology, pg 120-126, 2008).
Teaser - I am now compiling the henna research q&a- It is verrryyy interesting, stay tuned