The influence of 3-(trimethoxysilyl) propyl methacrylate and benzoyl peroxide on gel content, crystallinity, and mechanical performance of unfilled PP-PE blends, and their composites with wood was investigated. All materials were compounded in a twin screw extruder and then injection molded. Specimens were then exposed to high-humidity and elevated temperature in a humidity chamber to cross-link any unhydrolyzed silane. Adding wood to the PE-PP blends, increased premature cross-linking but also increased gel contents. However, the gel contents of the composites were still low. The PP component did not appear to cross-link well and our gels were almost entirely HDPE. Fourier Transfer Infrared (FTIR) spectra provided additional evidence that TMSPM is grafted and cross-linked in unfilled PE-PP blends. Unfortunately, the spectra of wood composites proved difficult to interpret because of the complexity and overlap of the FTIR spectra of the wood. The HDPE component annealed when exposed to high-humidity and elevated temperature, although less so in samples with high-gel contents, presumably because of the decreased mobility. Annealing influenced mechanical performance, especially increasing moduli. Adding peroxide and silane appeared to improve adhesion between the wood flour and matrix in the composites but had little effect on energy absorbed during high-speed puncture tests. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1398-1409, 2011