Effect on Mold Shrinkage

There is a belief that increased particle size provides lower mold shrinkage because of a better flow (lower viscosity). However, in reality a connection between the two is more complex. It was shown that when average wood flour particle size increased from abont 50-60 pm to about 200 pm, mold shrinkage decreased from 0.58  

02% to 0.47 + 0.02%, and with fnrther increase to 500 pm, mold shrinkage either stayed the same or even slightly increased, to abont 0.49 0.02% [133]. 

Bulk density of wood flonr is typically aronnd 0.1-0.3 g/cml Aspect ratio of wood flonr (length to thickness of fibers) is typically between 3 1 and 5 1. Specific gravity (density) of wood is abont 1.3-1.4 g/cml When ashed (commonly at tem-peratnres between 525 and 575°C), wood often leaves 0.25-0.50% of mineral resi-dnes. For example, ashing of Trex boards, containing reportedly 50% of wood flour, produced 0.55 0.02% of ash. 

Wood often contains tannins, and higher levels of tannins are commonly associated with oak. Tannins are water-soluble phenolic and polyphenolic compounds, which can form dark color complexes with iron salts (ferric salts). That is why some WPG deck 

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Of all the variables, wall thickness has the most significant effect on mold shrinkage. More specific data on mold shrinkage are available in Chapter 5, Processing . 

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