powershell function parameter types

have the following function:

function appendToSB([System.Text.StringBuilder]$sb,
                    [string]$value){
    [void]$sb.append($value)
    $sb
}

$sb = new-object -typename system.text.stringbuilder
$sb = appendToSb($sb, "1,")

$sb.tostring() | out-host

i want to build string using StringBuilder using my function for that, but i receive the following error:

appendToSB : Cannot process argument transformation on parameter 'sb'. Cannot convert the "System.Object[]" value of ty pe "System.Object[]" to type "System.Text.StringBuilder". At E:\powershell\test.ps1:8 char:11 + appendToSb([system.text.stringbuilder]$sb, "1,") + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidData: (:) [appendToSB], ParameterBindingArgumentTransformationException + FullyQualifiedErrorId : ParameterArgumentTransformationError,appendToSB

does anybody can explain how function/function parameter/return values works in powershell?