6. Among all triangles formed by any three of the 8 vertices of a parallelepiped, the maximum possible number of acute triangles is $\qquad$ .


6. 32 Detailed Explanation: There are a total of $C_{8}^{3}=56$ triangles, with at least two non-acute triangles on each face, and at least 2 non-acute triangles on each diagonal face, so there are at least 24 non-acute triangles, and there can be at most 32 acute triangles, which is clearly achievable.